Crank mechanism (KShM). During the operation of a diesel engine, natural wear of cylinder liners, pistons, piston rings, crankshaft journals and bearings, piston pins and bearing surfaces of the piston bosses. With the deterioration of the technical condition of the parts of the crank mechanism, the consumption (waste) of crankcase oil increases; smoke from the breather becomes noticeable; compression in the cylinders and oil pressure in the main line are reduced; diesel engine becomes noisier. These symptoms, as a rule, are clearly manifested at the end of the diesel engine's service life or in case of accidental damage to crankshaft parts.
Reliably works until the overhaul of the diesel engine only with its rational use, timely and quality service units and systems that affect the wear rate of mechanism parts.
During operation, the technical condition of the crank mechanism is determined without disassembling the diesel engine by indirect indicators, using electronic devices and the simplest mechanical devices.
During shift maintenance (ETO), they listen to the operation of the diesel engine and pay attention to increased knocks in the areas where the crankshaft bearings and the upper heads of the connecting rod are located. Raised and dull knocks, as a rule, are heard only with significant gaps or with emergency damage to the bearings.
During the first and second maintenance (TO-1 and TO-2), the oil pressure in the main line is checked lubrication system. A decrease in oil pressure to 0.15 ... 0.1 MPa for a warm diesel engine with serviceable lubrication system units and correct pressure gauge readings indicates significant wear of the crankshaft bearings.
During the third maintenance (TO-3), the technical condition is checked cylinder-piston group by the amount of gases breaking through into the crankcase of a diesel engine. The amount of gases is determined by the gas flow indicator at the rated speed of the crankshaft. The indicator is installed on the oil filler neck instead of the cap.
During measurements, close the breather hole and the hole for the oil gauge with stoppers. The clearances in the connecting rod bearings and the upper heads of the connecting rod are checked with a special device without disassembling the diesel engine. With an increase in the clearances in the crankshaft bearings of more than acceptable values and strong smoke from the breather, the diesel engine is sent for repair.
Diesel timing mechanism. The main indicators of the technical condition of the gas distribution mechanism are the gaps between the valve stems and rocker heads, valve timing, wear of the cams, the tightness of the valves to the head seats, the condition of the cylinder head, sealing gasket, distribution gears, etc. Wear and tear of parts and a violation of the adjustment of the gas distribution mechanism lead to a decrease diesel power and fuel economy.
At TO-2, they check and, if necessary, adjust the gaps between the valve stems and rocker strikers. To assess the size of the gaps in the valve mechanism without removing the cover, use an autostethoscope. Knocks are heard from a running diesel engine at a low crankshaft speed, applying the tip of an autostethoscope to the valve box. With large gaps in the valve mechanism, clear metal knocks are heard. It should be remembered that for best job diesel engine, it is necessary to set the clearances recommended by the manufacturer in the valve mechanism.
At TO-3, valve leaks, valve timing, wear of gears, bearings and camshaft cams are checked.
Valve leaks are assessed by the leakage of compressed air supplied to the tested cylinder with the valves closed at a pressure of 0.2 MPa using a compressor-vacuum unit. The air flow rate is determined on the exhaust pipe or on the inlet pipe of the air cleaner using a gas flow indicator. In case of leaks exceeding the permissible value, the cylinder head is repaired. The valve timing will be checked by the angle of the beginning of the opening of the intake valves of the first and last cylinders.
The wear of the camshaft cams without removal from the diesel engine is determined by the amount of valve movement, taking into account the gaps between the rods and rocker heads.
The total wear of the timing gears, bearings and camshaft cams is determined by the phase shift in the direction of delay. [Semenov V.M., Vlasenko V.N. Tractor. 1989]
Maintenance and current repair of crank and gas distribution mechanisms
The crankshaft (KShM) and gas distribution (timing) mechanisms are the main ones for the engine. Any wear and tear of their constituent parts immediately leads to a decrease in power, economic and environmental performance, and failure of these parts leads to engine shutdown and cessation of the transport process.
The main KShM malfunctions include wear of cylinders, pistons, piston rings, piston pins, connecting rod head bushings, connecting rod and main bearings, crankshaft journals.
The main KShM failures are: breakage of the piston end, jamming of the pistons, melting of liners, scuffing of the cylinder mirror, cracks in the block or cylinder head of the block.
In the event of malfunctions, characteristic noises and knocks appear during engine operation, compression in the cylinders decreases, gas breakthrough into the crankcase from the over-piston space increases, oil burnout increases.
The main malfunctions of the timing are wear of the valve lifters and their guide bushings, valve plates and their seats, cams and camshaft bearing journals, gas distribution gears, changes in thermal gaps between the valve stems and pushers (or rocker arms), wear of valve stem seals. When the teeth of the timing gears break, the chain or belt transmission of the timing gears breaks, the valves burn out, the valve springs break, the valve timing is disturbed and, as a result, the fuel consumption increases sharply, the engine power decreases, up to its complete stop.
Characteristic features timing malfunctions are emerging knocks, pops and flashes in the intake pipe and muffler.
Diagnostics of the technical condition of the crankshaft and timing belt is carried out by characteristic knocks using stethoscopes, by compression, by air leaks from the over-piston space, by gas breakthrough into the engine crankcase, by oil burnout and other parameters.
Engine compression, which depends on the wear of the cylinder-piston group, the tightness of the valve seat and the condition of the block head gasket, is measured using compression meters (Fig. 2.14) or compressographs (recording pressure gauges).
a - diagram of the compression gauge; b - general view of the device
1 - spool; 2 - rubber conical bushing; 3- check valve; 4 - screw for resetting readings; 5 - body; 6 - pressure gauge
Figure 2.14 - Compressometer device
The spool 1 is necessary so that the flow from the cylinder fuel-air mixture did not leave the body of the device until the pressure gauge readings stabilized.
When checking compression, the engine must be warmed up to normal operating temperature(80 ... 90 ° С) and the air and throttle dampers must be fully open. The compression gauge is inserted alternately into the spark plug holes of the engine and rotated crankshaft starter. When checking compression in diesel engines, the compression gauge is fixed due to high pressures (2.0 ... 2.5 MPa) in the same way as the nozzle.
Compression value for gasoline engines lies in the range from 0.8 to 1.2 MPa, and diesel - 2.5 ... 3.5 MPa. The difference in compression between the cylinders should not exceed 0.1 MPa for gasoline engines and 0.3 MPa for diesel engines. If there is no data on the compression value, then its standard values in MPa can be roughly determined:
P c \u003d e × k, (2.11)
Where e- the compression ratio of the given engine;
To– coefficient accepted in the range of 0.1…0.12.
If the compression is less than the standard, then it is necessary to pour 15 ... 20 grams for a truck and 8 ... 10 grams for a passenger car into the tested cylinder of the same oil that is poured into the engine crankcase, and repeat the tests. The oil will seal the gaps between the piston, rings and cylinder. Therefore, if the compression increases significantly, then this will indicate wear of the cylinder-piston group (CPG), and if not, then a loose fit of the valves.
The relative amount of compression in percent is measured on a motor-tester by the amplitude of the starter current ripples consumed when cranking the crankshaft. The highest compression of all cylinders is taken as 100%, therefore the accuracy of this method is lower due to the different degree of charge of the battery.
More accurate and more versatile is the method of diagnosing compressed air leaks. Existing devices (K-69M and K-272) have almost the same functional diagram (Fig. 2.15)
1 - quick coupling; 2 - inlet fitting; 3 - reducer; 4 - inlet nozzle; 5 - measuring manometer; 6 - damper; 7 - adjusting screw; 8 - outlet fitting; 9 - coupling; 10 - fitting; 11 - rubber seal
Figure 2.15 - Device K-69M NIIAT
When testing, compressed air of a certain pressure (0.16 MPa) is supplied through the spark plug holes, which is maintained by the pneumatic reducer 3, and the flow rate provided by the presence of the calibration pipeline and the adjustment screw 7.
The device is powered by a compressor with a pressure of 0.3 ... 0.6 MPa. The pressure gauge scale can be normalized as a percentage. 0% corresponds to a pressure of 0.16 MPa, and 100% corresponds to 0 MPa. The piston of each cylinder is alternately set to the start of compression position (when the intake valve closed) and the TDC position of the compression stroke. To install the piston of each cylinder in these positions, the simplest devices included in the instrument kit are used. In each position fix the air pressure Y 1 and Y 2 . If there are leaks, then the air will leave through them and the pressure will drop. The more the pressure drops, the higher the wear of the CPG and (or) the timing. According to the difference in leaks DУ \u003d Y 2 - Y 1, the wear of the cylinder is judged, since near the TDC the cylinder wear is greater. It should not exceed 15 ... 30%. The amount of leakage at the position of the piston at TDC of the end of the compression stroke (U 2) depends on the cylinder diameter and should not exceed 25 ... 40% (higher values \u200b\u200bfor large diameters). According to the value Y 1 (no more than 10 ... 15%), the condition of the piston rings and valves is assessed. If the value Y 1 exceeds the allowable value, then the piston in the tested cylinder is installed at the end of the compression stroke and air is supplied there bypassing the device at a pressure of 0.3 ... 0.5 MPa. To prevent the piston from going down, it is necessary to engage first gear and parking brake. If the piston rings are worn, air noise is heard in the oil filler neck. If the gasket burns out, then air noise will be heard in the filler neck of the radiator (expansion tank) or at the junction of the head with the cylinder block.
In the event of leaks in the valve seats, the fluffs of the indicators (included in the instrument kit) fluctuate, inserted into the spark plug holes of adjacent cylinders, where the intake or exhaust valves are open in a given position of the cylinder being checked. A table with the valve test sequence for various engines is available on the front panel of the instrument.
The breakthrough of gases into the crankcase is determined using a gas flow meter (KI-4887) or a gas meter (GKF-6). At the same time, the pipe of the crankcase ventilation system is disconnected and the openings of the valve covers, oil dipstick, crankcase ventilation pipe, etc. are closed with plugs (included in the kit of the KI-4887 device), so that the crankcase gases exit only through the oil filler neck, to which the device inlet is connected (Fig. .2.16).
The principle of operation of the flowmeter is based on the dependence of the volume of gas passing through the throttle of the device depending on the area of the passing section S at a given pressure difference DP before and after the throttle:
, (2.12)
where m - expiration coefficient (0.62 ... 0.65);
Q is the volume of gas, m3/s;
S- area of the flow section, m 2;
r- density of the gas mixture, kg/m 3 ;
D R- pressure difference, Pa.
A vacuum pump is connected to the outlet of the device. The performance of the vacuum pump is constant, and the volume of escaping gases is different engines having a different technical condition - different. Therefore, in order for all the bursting gases to be immediately pumped out by the pump through the device, the throttle 2 is slightly opened or closed so that the water level in tubes 6 and 7 becomes the same (i.e., the pressure in the crankcase becomes equal to atmospheric pressure).
1 – device case; 2 - inlet throttle for creating atmospheric pressure in the crankcase; 3 - choke to create a fixed difference D R; 4 – flow meter scale crankcase gases; 5, 6, 7 - piezometers
Figure 2.16 - Scheme of the gas flow meter KI-4887
Turning throttle 3 sets a fixed differential pressure D R= 15 mm water column. The greater the breakthrough of gases, the lower the vacuum in front of the throttle 3 and the greater the angle it is necessary to turn it (increasing the flow area S) in order to provide the specified value D R. An arrow is connected to the throttle 3, which, on the scale of the device, will indicate the volume of gases in l / min. For most engines, the limit is 80…120 l/min.
Oil waste, which characterizes the wear of the cylinder-piston group, is controlled by its level in the engine crankcase. Oil waste is considered acceptable, amounting to 0.5 ... 1% of the amount of fuel consumed, and large values correspond to diesel engines. The method is not applicable if there is oil leakage from the system.
Maintenance of the CV and timing includes checking and tightening the fasteners, their constituent elements, adjustment and lubrication.
Fastening work is carried out to check the condition of fastenings of all engine connections: engine mounts to the frame, cylinder head, oil pan to the block, intake and exhaust pipeline flanges, etc.
To prevent the passage of gases and coolant through the cylinder head gasket, check and, if necessary, tighten the nuts securing it to the block with a certain moment. This is done using a torque wrench. The moment and sequence of tightening the nuts are set by the manufacturers (Fig. 2.17). The cast-iron cylinder head is fastened in a hot state, and from an aluminum alloy - in a cold state.
Checking the tightening of the bolts for fastening the oil pan in order to avoid its deformation and leakage is also carried out in compliance with a certain sequence, which consists in alternately tightening diametrically located bolts and in two or three steps.
release side
a - VAZ engine; b - YaMZ-236 engine; c – KamAZ-740 engine; g - engine ZIL-130
Figure 2.17 - The sequence of tightening the nuts for fastening the heads to the engine block
Adjustment work is carried out after diagnosis. If a knock is detected in the valves, as well as during TO-2, check and adjust the thermal gaps between the ends of the valve stems and the toes of the rocker arms (Fig. 2.18). When adjusting the clearances, the piston of the 1st cylinder on the compression stroke is set to TDC, for which the crankshaft is rotated until the marks are aligned. In this position, the gaps between the valve stems and the toes of the rocker arms of the 1st cylinder are adjusted. The valve clearances of the remaining cylinders are adjusted in sequence corresponding to the order of operation of the cylinders, turning the crankshaft 1/2, 1/3 or 1/4 of a turn when moving from cylinder to cylinder for four, six and eight-cylinder engines, respectively.
1 - rod; 2 - locknut; 3 - adjusting screw;
4 - screwdriver; 5 - rocker; 6 - probe; 7 - valve
Figure 2.18 - Adjustment of thermal clearances of the timing
To adjust the clearances in the KamAZ-740 engine, the crankshaft is set to the position corresponding to the beginning of the fuel supply in the 1st cylinder, using a latch mounted on the flywheel housing. Then the crankshaft is turned through the hatch in the clutch housing by 60 ° and the valve clearances of the 1st and 5th cylinders are adjusted. Next, the crankshaft is rotated by 180, 360 and 540 °, adjusting the clearances in the 4th and 2nd, 6th and 3rd, 7th and 8th cylinders, respectively. Regardless of how the crankshaft is set to its original position, the valve must be fully closed for adjustment.
Typical work during the current repair of KShM and timing is the replacement of liners, pistons, piston rings, piston pins, liners of connecting rod and main bearings, valves, their seats and springs, pushers, as well as grinding and lapping of valves and their seats.
Engine repair is best done at a specialized site, where it is delivered after removal from the car. Before repairing the engine, it is necessary to drain the coolant from the cooling system and the oil from the lubrication system by unscrewing the appropriate drain plugs.
Disconnect the battery and all electrical wires from the electrical and ignition system devices installed on the engine. It is advisable to carry out these works at a specialized post for replacing engines, equipped with a floor lift or an inspection ditch and a beam crane (or hoist).
Having disconnected the engine, it is delivered to the repair site and subjected to external cleaning and washing, and then dismantled. Details such as pistons, liners, rings, connecting rods, piston pins, liners, valves, rods, rocker arms and pushers, if they are suitable for further use, are marked with paint, so that they can then be assembled together with those parts and in the places where they have run in . Connecting rod caps with connecting rods and main bearing caps must not be interchanged, as they are processed together during manufacture and are not unified.
After disassembly, the parts are cleaned of soot, resinous deposits and dirt by mechanical and chemical methods.
Replacement of the cylinder liner is carried out when their wear exceeds the allowable, in the presence of chips, cracks of any size and scoring, as well as in the wear of the upper and lower landing belts.
The sleeves are pressed out using a special puller, the grips of which are hooked on the lower end of the sleeves.
A new sleeve is selected along the cylinder block so that its end protrudes above the plane of the connector with the block head. To do this, the sleeve is installed in the cylinder block without sealing rings, covered with a calibration plate and the gap between the plate and the cylinder block is measured with a feeler gauge. Sleeves installed in the block without sealing rings must turn freely. Before the final setting of the liners, the condition of the mounting holes for them in the cylinder block is checked. If they are damaged, they are restored by applying a layer of epoxy mixed with cast iron filings, which, after hardening, are cleaned flush. The edges of the upper part of the block, which are the first to come into contact with the rubber o-rings when the sleeve is pressed in, are cleaned with sandpaper to prevent damage to the o-rings during pressing. Sleeves with rubber sealing rings installed on them are pressed in using a press. When putting on the sealing rings, they must not be strongly stretched and twisted in the groove of the cylinder liner.
Piston replacement is carried out when deep burrs form on the surface of the skirt, the bottom and surface of the piston burn through, when the upper groove for the piston ring is worn.
Pistons are changed without removing the engine from the car. Pre-drain the oil from the oil pan, remove the block head and oil pan, unpin and unscrew the nuts connecting rod bolts, remove the cover of the lower head of the connecting rod and take out the damaged piston assembly with the connecting rod and piston rings upwards. The retaining rings are removed from the holes in the bosses, the piston pin is pressed out. If necessary, the bronze bushing of the upper head of the connecting rod is pressed out with the same press.
Pistons are selected according to the cylinder. Its size group must match the size group of the cylinder liner. The gap between the piston and the sleeve is checked with a tape probe (Fig. 2.19).
To do this, the piston is inserted into the cylinder with the head down so that the edge of the skirt coincides with the bottom of the sleeve, and the probe tape inserted between the sleeve and the piston is in a plane perpendicular to the axis of the pin.
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1 - dynamometer; 2 - probe tape
Figure 2.19 - Measuring the clearance between the cylinder and the piston
The probe tape is pulled with a dynamometer, fixing the pulling force, which should be in the range of 35 ... 45 N. The dimensions of the probe tape and the pulling force for different engine models are given in the operating and repair instructions. The thickness of the tape is 0.05 ... 0.08 mm, width - 10 ... 15 mm, length - 200 mm. If the pulling force differs from the recommended one, then take another piston of the same size group or, as an exception, of an adjacent size group and pick it up again in the cylinder.
Within the nominal and each repair size of liners and pistons for various engines, there can be up to six size groups. The diameters of the cylinders within each of them differ by 0.01 mm. The index of the size group (A, AA, B, BB, C, BB for liners and pistons of nominal size and G, YY, D, DD, E, EE for the 1st repair size, etc.) is indicated on the upper end of the sleeve and on the bottom of the piston. For passenger cars, cylinder diameters are divided into 3 ... 5 classes: A, B, C, D, E or 1, 2, 3, 4, 5 in increments of 0.15; 0.25; 0.35 or 0.4 mm.
All other car engines have similar size groups within each repair size.
When assembling the “piston - connecting rod” kit, the diameter of the hole in the piston bosses, the diameter of the piston pin and the diameter of the hole in the bronze bushing of the upper head of the connecting rod must also have one size group, which is marked with one paint on one of the piston bosses, on the ends of the pin and the upper head of the connecting rod.
When replacing the entire cylinder-piston group, the piston, pin, piston rings and sleeve supplied as spare parts in sets are selected in advance. Therefore, during assembly, the marking of parts is checked and the gap between the piston and the sleeve is checked with a probe tape. A properly selected piston should, under its own weight, slowly lower in the sleeve. The piston pin should smoothly enter the hole in the connecting rod upper head bushing under the pressure of the thumb. The connecting rod is checked for parallelism of the axes of the heads and, if the deformation exceeds the allowable one, the connecting rod is corrected. During assembly, the piston is placed in a bath of engine oil, heated to a temperature of 60 ° C and, using a mandrel, press the piston pin into the holes of the piston bosses and the upper head of the connecting rod. After that, retaining rings are inserted into the grooves of the bosses. If the landing of the finger in the connecting rod head is denser than in the piston, then the connecting rod is heated before assembly.
In the same way, the bushings of the upper head of the connecting rod and the piston pin are replaced. Unusable bushings are pressed out, and new ones are pressed in their place, while providing the necessary tightness. Then the bushings are bored on a horizontal boring machine or machined using a reamer. The inner surface of the sleeve must be clean, without scratches, with a roughness parameter of not more than Ra = 0.63 µm, and the ovality and taper of the hole should not exceed 0.004 mm.
Before installing the piston assembly with the connecting rod in the cylinder block, a set of piston rings is installed in the piston grooves. The gap between the compression ring and the piston groove is determined with a feeler gauge (Fig. 2.20), rolling ring 2 along the piston groove. The rings are also checked for clearance, for which they are inserted into the upper unworn part of the cylinder liner and the fit is visually assessed.
1 - probe; 2 - compression ring
Figure 2.20 - Measuring the gap between the ring and the piston groove
The gap in the lock is determined with a feeler gauge, and if it is less than the permissible value, then the ends of the rings are ground off. After that, the ring is re-checked for clearance and only then, using a special device that opens the ring by the ends in the lock, it is installed in the grooves of the pistons with the chamfer up. They must rotate freely in the piston grooves. Ring sets of nominal size are used if the cylinders have not been bored. Oversized rings are installed in the bored cylinders, corresponding to the new diameter of the cylinder. The joints of the compression rings are evenly spaced around the circumference. Installation of pistons complete with rings in the engine cylinders is carried out using a special tool (Fig. 2.21).
1 - sleeve; 2 - mandrel; 3 - piston assembly
Figure 2.21 - Installing the piston with rings and connecting rod in the cylinder
The replacement of the crankshaft liners is carried out with a knock of the bearings and a pressure drop in the oil line below 0.05 MPa at an idle speed and a properly operating oil pump and pressure reducing valves. In this case, the nominal clearance between the liners and the main journal exceeds 0.026-0.12 mm and between the liners and the connecting rod neck -0.026-0.11 mm, depending on the engine model.
The clearance in the crankshaft bearings is determined using control brass or copper foil plates 0.025 thick; 0.05; 0.075 mm, 6-7 mm wide and 5 mm shorter than the insert width. The plate, lubricated with oil, is placed between the shaft neck and the liner, the bearing cover bolts are tightened with a torque wrench with a torque specific for each engine. If, for example, a plate with a thickness of 0.025 mm is installed, the crankshaft rotates too easily, then the gap is greater than 0.025 mm and, therefore, the plate should be replaced with the next size until the shaft rotates with a noticeable effort, which corresponds to the actual gap between the neck and the liner. When checking one bearing, the bolts of the others must be loosened. All bearings are checked in the same way. Instead of brass or copper plates, a special calibrated plastic wire can be used. Its small segment, equal to the width of the liner, is placed on the neck in the axial direction and pressed with a connecting rod or main bearing cover, depending on where the clearance is measured. Being careful not to move the wire, secure the cover and tighten it using the assembly torque. The wire is flattened. Then the cover is removed and the gap in the mating is estimated from the changed wire thickness, comparing the thickness of the flattened wire with the scale printed on the commercial packaging of the wire.
The surface of the crankshaft journals must be free of burrs. In the presence of scoring and wear, replace or restore the crankshaft.
Before assembly, the liners of the required size are washed, wiped and installed in the bed of the indigenous and connecting rod bearings, having previously lubricated the surface of the liner and neck with engine oil.
The axial play of the crankshaft of a number of engines is adjusted by selecting thrust washers. The gap between the front thrust end of the crankshaft and the rear thrust washer should be within 0.075-0.250 mm.
For YaMZ engines, the axial clearance of the crankshaft is adjusted depending on the length of the rear main journal by installing half rings. The axial clearance in the thrust bearing should be 0.08-0.23 mm.
During operation, due to wear, the axial clearance increases. With TR, it is regulated by installing thrust washers or half rings of repair sizes. Compared to the nominal size, they have an increased (by 0.1; 0.2; 0.3 mm, respectively) thickness.
The main malfunctions of the heads and the block are cracks on the mating surface with the cylinder block, cracks on the cooling jacket, warping of the mating surface with the cylinder block, wear of the holes in the valve guide bushings, wear and shells on the chamfers of the valve seats, weakening of the fit of the valve seats in the sockets.
Cracks no longer than 150 mm located on the mating surface of the cylinder head with the block are welded. Before welding, holes with a diameter of 4 mm are drilled at the ends of the cracks in the head made of aluminum alloy and cut along its entire length to a depth of 3 mm at an angle of 90 °. seam direct current reverse polarity using special electrodes.
In gas welding, AL4 brand wire with a diameter of 6 mm is used, and AF-4A is used as a flux. After welding, the flux residues are removed from the seam and washed with a 10% solution of nitric acid, and then hot water. Finally, the seam is cleaned flush with the base metal with a grinding wheel.
Cracks up to 150 mm long, located on the surface of the cylinder head cooling jacket, are sealed with epoxy paste. The crack is preliminarily cut in the same way as for welding, degreased with acetone, two layers of epoxy composition mixed with aluminum filings are applied. Then the head is kept for 48 hours at 18-20 °C.
Warping of the mating plane of the head with the cylinder block is eliminated by grinding or milling. After processing, the heads are checked on a control plate. A probe 0.15 mm thick must not pass between the plane of the head and the plate.
If the holes in the valve guides are worn out, replace them with new ones. The holes of the new bushings are unrolled to the nominal or repair dimensions. For pressing and pressing the guides, a mandrel and a hydraulic press are used.
Wear and shells on the chamfers of valve seats are eliminated by lapping or grinding. Grinding is performed using special devices that allow the working body to perform reciprocating and rotational movements, an electric or pneumatic drill, on the spindle of which a suction cup is installed. For lapping valves, GOI paste or lapping paste is used (15 g of micropowder of white electrocorundum M20 or M12, 15 g of M40 boron carbide and engine oil). The ground-in valve and seat must have an even matte strip of at least 1.5 mm along the entire circumference of the chamfer.
The quality of grinding is checked by an excess air pressure of 0.15 ... 0.20 MPa created above the valve. It should not noticeably decrease within 1 min.
The saddles are countersinked if it is not possible to restore the chamfers of the saddles by lapping. After countersinking, the working chamfers of the valve seats are ground with abrasive wheels at an appropriate angle, and then the valves are ground. To restore the saddles, special devices with a set of cutters for the formation of working and auxiliary chamfers with different angles of inclination can also be used. If there are shells on the chamfer and when the seat is loosened in the seat of the block head, it is pressed out with a puller. The hole is bored under the saddle of the repair size. Repair size saddles made of high-strength cast iron are pressed into a preheated block head using a special mandrel, and then the seat chamfer is formed by countersinking.
Typical valve malfunctions are wear and shells on the valve chamfer, wear and deformation of the valve stems, wear of the valve end. When the valves are faulty, the straightness of the rod and the beating of the working chamfer of the head relative to the rod are checked. If the runout is more than acceptable, the valve is corrected. When the valve stem is worn, it is ground to the repair size on a centerless grinding machine. The worn end of the valve stem is ground on a grinding machine.
Valve guides wear on the inside surface. When the gap between the valve stem and the guide sleeve is more than 0.15 ... 0.20 mm, it is restored. If the release of oversize valves is provided for engine repair, then the sleeve is turned to a new oversize. Otherwise, the bushing is replaced.
Worn bronze bushings in the rocker arms are replaced with new ones and bored to the nominal or repair size.
Repairs of crankshafts and camshafts. Worn main and connecting rod journals crankshafts, as well as the bearing journals of the camshafts, are ground to the repair dimensions. After grinding, the necks are polished with an abrasive belt. Worn camshaft cams are ground on a copy-grinding machine.
crank engine piston repair
During the operation of the engine in the cylinder-piston group (CPG), crank mechanism(KSHM), the gas distribution mechanism (GRM), auxiliary units and assemblies, defects appear, the external signs of which, as a rule, are the appearance of various noises and knocks coming from various zones of these systems.
The practice of car operation shows that approximately 30% of all failures and malfunctions occur in the engine and its systems.
The main failures and malfunctions of the KShM include: wear, jamming, melting of liners; deformation of the beds of main bearings in the cylinder block; wear and deformation of the crankshaft; deformation and wear of the holes of the lower and upper heads of the connecting rod; deformation of the connecting rod; broken connecting rod bolts; wear, jamming, destruction of balancing shaft bearings
CPG is characterized by the appearance of destruction of bridges, cracks in the piston, burning of its bottom, wear of pistons, rings, cylinders, piston pins, destruction of piston rings, deformation of the piston skirt, scuffing on the skirt and cylinder surface, the occurrence of holes, cracks in the cylinder or block; warpage of block surfaces; loss of piston pin retainers in the piston.
The main signs of a malfunction of the KShM and CPG are: a drop in compression in the cylinders; the appearance of extraneous noise, knocks and vibrations during engine operation; an increase in oil consumption for waste with the appearance of bluish smoke at the outlet; decrease in oil pressure at idle, due to its dilution; "Oiling" candles and nozzles; insufficient acceleration dynamics.
The timing belt has a significant list of failures and malfunctions: wear of the seat, valve, guide bushings, valve stem seals; destruction, burnout of valves; destruction, settling of springs; wear, overheating, destruction of camshaft bearings; wear of camshaft cams and pushers; wear of rocker arms and their axles; destruction of the valve seat; jamming of hydraulic pushers; wear of the chain (belt) and sprockets (toothed pulleys) of the camshaft drive; jamming of the tensioner and wear of its plunger; burnout of the cylinder head; cracks, holes in the head of the block, warping of the planes of the head of the block.
Signs of a malfunction of the timing system are also noises, knocks, flashes during intake system and pops in the exhaust system.
A common symptom of KShM, CPG and timing malfunctions is an increase in fuel consumption and a decrease in engine power.
Maintenance. To prevent failures and malfunctions of the engine at motor transport enterprises, a complex of control and preventive work is carried out, which includes diagnostics (D-1, D-2); Engine EO; TO-1, TO-2, ETO.
When performing maintenance operations, much attention is paid to fixing and control and adjustment work.
Tightening nuts and bolts for fastening various engine elements during maintenance operations applies mainly to domestically produced cars. These works are carried out torque wrench tightening torque prescribed in the Instruction Manual. Bolts (fastening elements) are tightened evenly and sequentially from the middle to the edges in two to four steps. The pressing force depends on the coefficients of thermal expansion of the metals of the cylinder head and fasteners. Therefore, the fastening elements of the cast-iron head are tightened on a warm engine, and from an aluminum alloy on a cold one.
The same operation for foreign-made engines is carried out only for cases of removing the head of the block (during repair operations) and then installing it in place. In this case, the tightening of the head of the block is carried out in three stages: a) tightening of all fastening elements with a nominal torque (determined by the Manual); b) complete release of all fasteners in reverse tightening sequence; c) tightening all fastening elements with a torque wrench to half the nominal value; d) turning the same fastening elements strictly at an angle of 900 with a key with an angular indication of rotation.
Loosening and tightening the fastening of the oil pan (in order to avoid its deformation, it is also carried out by alternately tightening the diametrically opposite fastening elements.
The adjustment of the thermal clearances of the valve actuator of the gas distribution mechanism (without hydraulic compensators) is carried out on a cold engine with the valves completely closed. Before starting the adjustment, the piston of the first cylinder is brought to the position top dead point (TDC) of the end of the compression stroke (the rotation of the crankshaft must be carried out strictly clockwise). The gap, as a rule, is measured with a flat feeler gauge (it is also possible to use a device with a dial indicator head).
The stylus plate, the thickness of which is equal to the required gap, should pass into the gap with light pressure. The probe should be inserted and pulled out of the gap with a force of 0.2 - 0.3 kgf (1.9 - 2.9 N) (in this case, a slight pinching of the probe should be felt).
The principle of adjusting the thermal clearances of the valve mechanism depends on the type of valve drive and the location of the camshaft. For example, for engines with a lower (lateral) camshaft, the clearance is adjusted by using a feeler gauge. For engines with an upper camshaft, the clearance is adjusted by rotating the adjusting screw and then fixing it with a lock nut.
In some cases, the adjustment of thermal clearances is regulated by selecting the thickness of the shims installed between the camshaft cams and the cylindrical pusher.
Example: Assume A = 0.3mm, B = 3.8mm, C = 0.2mm (for inlet valve), Then
H \u003d 3.75 + (0.3 - 0.2) \u003d 3.85 mm
Within the step of the difference in the thickness of the washers equal to ± 0.05 mm, we select the thickness of the new washer equal to 3.85 mm.
The thickness of the bottom of the pusher is determined by the number stamped on the inside of its bottom, i.e., for example, the designation 788T should be understood as 7.88 mm of the thickness of the bottom of the pusher. The step of the difference in the thickness of the bottom of the pusher is assumed to be ± 0.02 mm.
Modern engines use bush-roller chains or toothed belts as a drive for the camshaft (shafts) of the timing and its other attachments. During operation, both chains and belts are stretched, which leads, in particular, to a shift (change) in the setting of the gas exchange phases. Therefore, these drive elements require periodic monitoring of their technical condition and tension. There are several schemes for tensioning chains or drive belts, one of which involves the presence of a tensioner with a fixing nut on its rod or locking screw. Before checking, it is necessary to cool the engine within 30 minutes after stopping it. Then it is necessary to inspect all belts for wear, destruction, cracks on the contact and side surfaces. Apply a force of 98 N (10 kgf) in the control points, and measure the belt deflection.
When using automatic tensioners, their hydro-mechanical drive provides tension to the chain or drive belt due to the force of the spring and the supply of oil under pressure under the plunger, so there is no need to carry out this operation during maintenance.
Maintenance. Most of the maintenance work is carried out on the engine removed from the car, because it is easier and more convenient. In the absence of obvious damage to the crankshaft and cylinder block, the current repair consists in disassembling the engine (removing the pulleys and front cover of the engine, cylinder head, oil pan, pistons with connecting rods, replacing or boring cylinder liners).
Replacement of the cylinder-piston group is necessary when the working surface is worn out more than the permissible limit, in the presence of scoring, chips, cracks on the cylinder mirror. The amount of wear of cylinders and liners is determined by an indicator caliper (see workbook laboratory work at the rate).
When replacing worn pistons, they are selected together with piston pins, with retaining and piston rings (see the same workbook).
Replacement of liners when they are worn beyond the established limit. This leads to a drop in pressure in the oil line, the appearance of a low-pitched metallic knock for the main ones and a higher one for the connecting rod bearings. Inserts are replaced only in pairs (see the same workbook). Bolts and nuts for fastening the bearings are tightened evenly from the middle to the edges in two or three stages to the nominal torque, which is set either by a torque wrench or by turning to a certain angle.
Block head repair. During operation, the following main malfunctions of the cylinder head are detected: - deformation of the surface (non-flatness) of the gas joint; - wear of the working surface of the valve guides; - wear of valve seats and valve plates.
The deformation of the surfaces of the head of the block is eliminated either on a lapping plate using an abrasive paste (20 - 40 microns), or by grinding to a depth of not more than 0.15 mm until traces of non-flatness (0.04-0.05 mm) are removed.
Wear of the valve guides in the head of the block leads to a violation of the seal of the valve stem, an increase in oil consumption and increased noise from the engine. The worn bushing is replaced by heating-cooling the bushing head to create an acceptable tightness when it is pressed in.
The valve seats and the valves themselves change their shape, as a result of which the tightness of the seat-valve assembly is violated. The main repair methods for valve seats are milling, grinding and lapping.
Milling cutters with 30, 45 and 600 angles are used, which provide a traditional saddle shape.
Repair of local damage to tires allows you to eliminate cuts up to 110 x 20 mm, gaps up to 50 x 40 mm. The recovery sequence is as follows. Remove stuck items. Round the edges of the tears to prevent their growth. The contour of damage is treated to the full depth, smeared with glue, covered with special cushioning rubber. All free space of the damage is filled with a rubber compound.
The quality control of the fit of the valve to the seat after grinding can be carried out in several ways: by the indicator of a special vacuum device; by paint, by “pencil”, as well as by leakage of kerosene (white spirit) poured into the inlet or outlet channels with the valves and springs assembled.
The easiest is to check with a soft pencil, in which 6-8 radial lines are evenly applied to the valve face. After installing the valve, it is necessary to press its plate and turn the valve 1800 in both directions. With proper assembly and lapping, all lines will be erased.
TO Category:
Car maintenance
Maintenance of the crank mechanism
During operation reliable performance crank mechanism is ensured by timely care of it, the use of oils recommended by the manufacturer for lubrication.
Malfunctions in the crank mechanism occur as a result of wear of the piston rings, pistons and cylinder liners, main and connecting rod bearings and crankshaft journals, piston pins, holes in the piston bosses or bronze bushings of the upper head of the connecting rod, damage to the gaskets of the cylinder heads or loosening of the heads block. External signs of these malfunctions are characteristic knocks that are heard with a stethoscope. Its tip is touched to various places of the engine and the type of malfunction is determined by the nature of the knock or noise.
In order to correctly determine the cause of its occurrence by knocking (noise), you need to know the nature of knocks during various malfunctions. So, piston knocks are characterized by a dull clicking sound, which is heard above the plane of the crankcase connector with a sharp decrease in the crankshaft speed immediately after starting a cold engine.
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The knock of the main bearings is accompanied by a strong, dull, low-pitched sound, heard in the plane of the engine crankcase connector with a sharp change in the crankshaft speed.
The knock of the connecting rod bearings is sharper and louder than the knock of the main bearings. It is audible in the zone of rotation of the crank of the corresponding cylinder. The disappearance or a noticeable decrease in knocking when the ignition or nozzle is turned off in this cylinder indicates a bearing failure.
The knock of the piston pin, sharp, sonorous, high-pitched, is heard in the area of \u200b\u200bthe cylinders, in places corresponding to the upper and lower positions of the piston pin, when the engine crankshaft speed changes. However, this knock should not be confused with detonation knocks, which appear at a large ignition timing and disappear when it is reduced.
Minimum crankshaft speed per Idling carburetor engines should be 400-450 rpm, and for diesel engines - 500-600 rpm.
All of the listed malfunctions associated with the wear of parts of the crank mechanism are eliminated during engine repair.
A decrease in engine power (the engine “pulls badly”) often occurs due to increased wear on the working surfaces of the parts of the cylinder-piston group - piston, cylinder liner, compression rings, as well as loose fitting of the valves to the seats, damage to the cylinder head gasket or loosening of the cylinder head . These faults cause a loss of compression - a decrease in pressure in the cylinder at the end of the compression stroke. Loss of compression also occurs when compression rings break or “stick” in the piston grooves, which is the result of engine overheating, the use of oil not specified by the manufacturer, or prolonged engine operation under load at low coolant temperatures. At the same time, carbon deposits are deposited in the combustion chamber on the walls of the head, cylinder, piston crown, valve heads, the formation of which also occurs due to wear of piston rings and cylinders, engine operation at elevated level oil in the crankcase, misfiring and running the engine rich.
Rice. 5. Compressometers:
a - for carburetor engines; b - for diesel engines; 1 - body; 2 - manometer; 3 - fitting; 4 - gaskets; 5 - lock nuts; b - tube; 7 - rubber tip; 8 - spool; 9 - spool rod; 10 - exhaust valve; 11 - hose; 12 - adapter; 13 - clamping nut; 14 - valve; 15 - valve spring; 16 - valve seat; 17 - tip
The compression pressure is checked using a compression gauge (Fig. 5) on a warm engine at a coolant temperature of 75-80 C. The check is performed when removed nozzle or a spark plug and a compression tester tip installed instead.
The normal compression pressure in the cylinders must be at least 3.0 MPa at a crankshaft speed of 500 rpm for KamAZ-740, YAME-236, 238 diesel engines. The difference in the compression gauge readings for the cylinders should not exceed 0.2 MPa. In the cylinders of carburetor engines, when cranking the crankshaft using a starter for 12-15 revolutions, the compression pressure (MPa) is: for the ZIL-130 engine 0.75-0.85, Ural-375 - 0.7, 3M3-53 - 0, 75-0.78. The difference in pressure between the cylinders is allowed 0.05 MPa.
The decrease in oil pressure in the system is mainly due to the increase in clearances in the crankshaft bearings during their wear. This malfunction is eliminated when the engine is repaired. However, first of all, you need to make sure that the required amount of oil is in the engine sump and that the pressure gauge is working.
Increased oil consumption and an increase in exhaust smoke can be the result of piston rings “bedding” or increased wear, as well as the result of oil leakage through leaks in the joints. The last malfunctions are eliminated by tightening fittings, plugs and fastenings of units and components of the lubrication system, connecting hoses, replacing sealing elements or worn piston rings.
To eliminate the "occurrence" of the piston rings, it is necessary to warm up the engine, and then pour 20-25 g of a mixture of equal parts of kerosene and denatured alcohol into each cylinder through the holes for candles or nozzles for 8-10 hours. After that, a little oil is poured into the cylinders, the engine is started and let it work for 20-25 minutes. The softened soot burns out and is thrown out with the exhaust gases. After completing the carbon removal operation, it is necessary to change the oil in the engine crankcase.
If this method does not give a positive result, then to remove carbon deposits, it is necessary to partially disassemble the engine with the removal of cylinder heads and gaskets. To soften the soot, it must be abundantly moistened with kerosene with a rag and, after a few hours, remove it with wooden or textolite scrapers from the piston bottoms, valve heads and cylinders. After cleaning, it is recommended to wash the surfaces of the parts with kerosene.
If the engine was running on leaded gasoline, then before cleaning the carbon deposits, it is necessary to moisten the parts in kerosene, while observing the rules for handling poisonous deposits of leaded gasoline.
Special care must be taken when removing the head gasket to avoid damaging the head gasket. Before setting the gasket, its surfaces on both sides are rubbed with graphite powder to prevent sticking to the surfaces of the head and cylinder block. The places of the gasket adjacent to the holes for the bolts or studs of the head of the block are lubricated on both sides with a special paste to prevent the penetration of water to the threaded connections.
The presence of water in the lubrication system may be the result of loosening of the bolts (nuts) fastening the cylinder heads, injector cups, the presence of cracks in the head or cylinder block, as well as a violation of the sealing of liners from cylinder blocks. Loose bolts (nuts) for fastening the cylinder heads and injector cups should be tightened, and malfunctions of the cylinder liners seals (rubber rings) or cracks in the cylinder liners and block heads are eliminated by engine repair.
The sequence of an inhaling of bolts (nuts) of fastening of a head of the block of cylinders is shown on fig. 6.
The tightness of the head to the surface of the block is provided correct tightening bolts (nuts) of fastening of heads of cylinders. To ensure even tightening and prevent warping of the head, start tightening from the middle of the head. For cast iron heads, the bolts (nuts) are tightened on a warm engine, and for aluminum alloy heads, on a cold one. The final tightening is done with a socket wrench with a torque handle.
Rice. 6. The order of tightening the bolts (nuts) for fastening the cylinder head of car engines:
a - GAZ-53-12, -66-11, -14 "Seagull"; b - ZIL-130, Ural-375D, buses LiAZ-677, LAZ-695N, -699R; c – MA3-5335; d - GAZ-24, -3102 Volga; e - KamAE-5320; f - ZIL-4331; g - Ikarus-260; 3 - socket wrench with torque handle
If the cylinder head is loosely tightened, the tightness of the cylinders can subsequently be violated, which can cause the gasket to burn out and coolant to enter the cylinder. As a result, starting the engine is difficult, the engine is unstable at low crankshaft speeds, and sometimes stops. With a strong tightening, the bolts (studs) stretch and may even break.
Novgorod production association Avtospetsoborudovanie developed and manufactured a device for determining the technical condition of the cylinder-piston group of engines - model K59M. It allows you to evaluate the technical condition of the cylinders, piston rings, cylinder head gaskets, valves and valve clearance adjustment. Portable, pneumatic. Operates on the principle of measuring the leakage of air injected into the cylinder idle engine through the spark plug or injector hole. The set of the device includes an air reducer; pressure gauge with a scale graduated in percentage of air leakage; adjusting screw; calibrated nozzle; inlet and outlet fittings; hose for connecting the device to the cylinder; a special fitting installed in the hole for the candle (injector); quick couplings designed to connect the compressed air line hose to the device and a special fitting; a sound signaling device for determining the end of the compression stroke in the first cylinder of the engine before the start of the test; a set of scales and an arrow installed in the housing and on the breaker cam to determine the beginning and end of the compression stroke in the cylinders carburetor engine; noise level indicator for the same purposes when checking a diesel engine; leakage indicator (with headphones).
Compressed air is supplied to the engine cylinder through a special gearbox or directly from the line. In the first case, the air pressure is reduced to 0.16 MPa, which, with complete tightness of the cylinder-piston group, corresponds to the zero mark of the pressure gauge scale and is a control mark for reporting the amount of air leakage when assessing the general condition of the cylinder-piston group. If air is supplied to the cylinder directly from the line, then the pressure in the cylinder of 0.45 MPa is set by the shut-off valve of the line according to the inlet pressure gauge, High blood pressure in the cylinder allows you to more clearly see and determine the breakthrough of air through the piston rings and cylinder head gasket by fluctuations in the fluff in the leak indicator.
Maintenance. At EO the engine is cleaned of dirt, its condition is checked visually and the operation is listened to in different modes.
At TO-1 perform EO work, and also check the tightness of the connection of the oil pan with the block or the crankshaft oil seals (no oil leaks), as well as the fastening of the engine to the frame. The fastening is checked without loosening the nuts. Tighten connections if necessary. Inspection determines the condition of the rubber elements, which should not have delamination and destruction of the rubber (if there are defects, they are replaced). Listen to the operation of the valve mechanism, if necessary, adjust the thermal clearances.
At TO-2 And SO perform all the work of TO-1, as well as check and, if necessary, tighten the fastenings of the cylinder heads, adjust the thermal gaps in the timing. Check and adjust the tension of the chain or the camshaft drive belt (if it is located at the top), tighten the fastening of the front engine cover (camshaft cover).
Diagnosis. When diagnosing the crank (KShM) and gas distribution (timing) mechanisms, they check the compression in the cylinders, the place and nature of noise and knocks, the technical condition of the engine in places and the amount of air leaks when it is supplied to the cylinders under a certain pressure, the elasticity of the valve springs and the volume of gases breaking into the crankcase.
compression engine ( maximum pressure in the cylinder at the end of the compression stroke) is determined by a compression gauge when turning the crankshaft with a starter, inserting the rubber cone tip of the compression gauge into the hole for the nozzle or spark plug (Fig. 50a). The compressor is equipped with a recorder for recording the pressure in the cylinders (Fig. 50b, c). To obtain the most reliable results, compression is determined on a warm engine by removing all spark plugs or injectors from it. The specified speed of the crankshaft is provided by a properly charged battery.
Before measuring compression in each cylinder, the pressure gauge must be set to zero. The minimum allowable compression for diesel engines is about 2 MPa, for gasoline and gas engines it depends on the degree of compression and is 0.6-1.0 MPa. The difference in pressure gauge readings in individual cylinders should not exceed 0.2 MPa for diesel engines and 0.1 MPa for gasoline and gas engines. Insufficient compression in the cylinders indicates wear on the liners, piston rings or valve leaks. A sharp decline compression (by 30-40%) indicates a breakdown or occurrence of piston rings.
Rice. 50. Compressometer (a) and compressographs (b, c)
The presence, location and nature of knocks and noises determined with the help of stethoscopes and vibroacoustic equipment (Fig. 51). By the nature of the knock or noise and the place of its occurrence, engine malfunctions are determined. Any extraneous noise and knocks in the engine during operation are unacceptable. With the help of a stethoscope, the increase in clearances in the connecting rod and main bearings of the crankshaft, between the piston and cylinder, valves and pushers, valves and bushings, etc. is determined.
Rice. 51. Stethoscopes for car diagnostics: a - mechanical; b - combined electronic
Knocks of pistons on the cylinder - deaf, clicking; they are heard on a cold engine at a low crankshaft speed or its sharp decrease. Knocks in the main bearings of the crankshaft - strong, deaf, low tone; they are heard on a warm engine with a sharp change in the crankshaft speed, as well as when individual cylinders are turned off. Knocks in connecting rod bearings are sharper than in main ones; appear with a sharp change in the speed of the crankshaft (when this cylinder is turned off, the knock disappears or noticeably decreases).
Knocks in the “piston pin - connecting rod” conjugation are sonorous, metallic; are heard with a sharp change in the speed of the crankshaft (disappear when the cylinder is turned off). Knocks when jamming intake valves - quiet, even; are audible at the locations of the valve bushings at idle. Knocks in the timing gears - frequent, merging into a general noise, indicate a lot of wear or breakage of the gear teeth. Knocks in the camshaft bearings - even, medium tone; are heard with an increase in the frequency of rotation of the crankshaft. Knocks in the interface “rocker striker - valve stem end” are sharp; are audible in all modes of operation and indicate an increased gap.
Leaks of air supplied to the cylinders under a pressure of 0.4 MPa are determined by special devices. Air leaks can reveal excessive wear, loss of elasticity, coking or breakage of piston rings, worn piston grooves, worn cylinders, leaks in valves and cylinder head gaskets. To determine the condition of the piston rings, set the piston to the beginning of the compression stroke and, supplying air to the cylinder, measure its leakage (pressure drop) with a manometer.
The scale of the device is marked into zones: good condition engine, satisfactory and in need of repair. Cylinder wear is determined in the same way, but when the piston is installed near the TDC of the compression stroke. Air leaks greater than 15% indicate severe cylinder wear. Air leaks through the valves are determined by ear, and the tightness of the cylinder head gasket is determined by the appearance of air bubbles in the radiator neck or at the junction (head with cylinder block) moistened with soapy water.
The state of the "piston - piston rings - cylinder liner" interface can be assessed by the amount of gases breaking through into the crankcase. This parameter is determined using flow meters (for example, KI-4887-1) after preheat engine. By measuring the amount of gases breaking into the crankcase, and comparing this value with the normative one, a conclusion is made about the state of the cylinder-piston group. The elasticity of the valve springs is determined by special devices (Fig. 52).
Rice. 52. Valve spring tester
When disassembling the engine, the geometric dimensions of the parts are diagnosed (measured) and, comparing the obtained values \u200b\u200bwith the nominal and permissible ones, they make a conclusion about their suitability for further operation (measurement of the shaft journals is carried out with micrometers, and the diameters of the holes - with micrometric inside meters).
Repair of the crank mechanism (KShM). Malfunctions of the crank mechanism- the most serious engine malfunctions. Their elimination is very time-consuming and costly, as it often involves a major overhaul of the engine.
The main malfunctions of the crank mechanism include:
Wear of main and connecting rod bearings;
Wear of pistons and cylinders;
Wear of piston pins;
Breakage and occurrence of piston rings.
Main reasons these faults are the development installed resource engine or violation of engine operation rules ( usage poor quality oil, increase in terms of maintenance, long-term use of the car under load, etc.).
Almost all malfunctions of the crank mechanism (KShM) can be diagnosed by external signs, as well as using the simplest instruments (stethoscope, compression gauge). KShM malfunctions are accompanied by extraneous noise and knocks, smoke, a drop in compression, increased consumption oils.
External signs and their corresponding KShM malfunctions are listed in Table 1.
Table 1
External signs and their corresponding KShM malfunctions
| Symptoms | Malfunction |
| · Deaf knock in the lower part of the block of cylinders (increases with an increase in speed and load). Reduced oil pressure (warning light on) | Wear of main bearings |
| · Floating thud in the middle of the cylinder block (increases with increasing speed and load, disappears when the corresponding spark plug is turned off). Reduced oil pressure (warning light on) | Wear of connecting rod bearings |
| · Loud knocking (clatter of earthenware) on a cold engine (disappears when warmed up). Blue smoke exhaust | Wear of pistons and cylinders |
| A loud knock in the upper part of the cylinder block at all engine operating modes (increases with increasing speed and load, disappears when the corresponding spark plug is turned off) | Piston pin wear |
| · Blue smoke from exhaust gases. · Reduced oil level in the engine crankcase. Intermittent engine operation | Breakage and occurrence of rings |
| Weak compression in the cylinders. The engine runs erratically and does not develop its rated power | Wear of parts of the piston group (sleeves, pistons, rings) |
| The engine suddenly stops | Piston jamming in the sleeve or crankshaft jamming |
| Oil leak at the junction of the pallet and block | Damage to the gasket or insufficient tightening of the bolts (nuts) of the pallet |
| Leakage of coolant from the block (head) | Cracks or holes in the block (block head) |
When diagnosing wear of the main and connecting rod bearings, further operation of the car is strictly prohibited. In other cases, with the utmost care, you must follow the repair site.
Repair of the crank mechanism consists mainly in identifying and replacing failed parts.
Completion of KShM parts.Pistons selection carried out by weight and size groups. Pistons are selected for each cylinder in accordance with the dimensions of the liners, since according to the technical conditions for assembling the crankshaft between the sleeve and the piston, there must be a certain gap. When replacing sleeves and pistons at the same time, they are completed according to size groups (sleeves and pistons must belong to the same size group). When boring cylinders, pistons are selected in strict accordance with the dimensions of the liners. All pistons installed on one engine must be matched by weight. The difference between the masses of the heaviest and lightest pistons of one set is allowed no more than 0.5%.
Selection of piston rings is carried out taking into account the dimensions of the piston and cylinder. When selecting rings along the piston, they are rolled along the piston groove and the gap between the end of the ring and the piston groove is measured with a feeler gauge (Fig. 53).
Rice. 53. Checking the backlash between the ring and the piston groove: 1 - piston ring, 2 - piston, 3 - set of probes
When selecting rings for a cylinder, the ring is installed in the zone of least wear of the cylinder (but within the stroke of the piston rings) and the gap in the ring lock is measured with a feeler gauge (Fig. 54). The required clearance values are indicated in the manuals for specific car brands.
Rice. 54. Checking the clearance in the piston ring lock: a - using a special mandrel; b - directly in the engine cylinder
Selection of piston pins and connecting rods. When repairing an engine, it is not recommended to depersonalize a set of its connecting rods, which are selected by weight at the factory. The replacement of individual connecting rods of one set is carried out taking into account the mass (weight adjustment is performed by removing the metal from the bosses on the cap and the connecting rod head). It is not allowed to interchange the connecting rod caps as the bottom cap and the cap are machined together at the factory. Connecting rods are sorted into size groups according to the diameter of the hole in the sleeve of the upper head and are marked with paint of a certain color. Piston pins (according to their outer diameter) and pistons (according to the inner diameter of the bosses) are divided into the same groups. The piston, pin and connecting rod of one set must belong to the same size group.
The assembly of the crank mechanism is carried out in the following sequence:
1. Assemble the connecting rod and piston group. The connection of the piston, pin and the upper head of the connecting rod is made when the connecting rod is heated to 240 ºС. The pin is pressed into the piston bosses and the upper head of the connecting rod using a special tool (Fig. 55). The finger is installed in the fixture, the connecting rod, heated to 240 ºС, is clamped in a vice, the piston is put on the connecting rod so that the hole for the finger coincides with the hole in the upper head of the connecting rod. With the tool, the piston pin is pushed into the piston bore and the upper head of the connecting rod so that the shoulder of the tool roller is in contact with the piston.
To properly connect the pin to the connecting rod, the pin should be pressed in as quickly as possible: after the connecting rod has cooled, it will no longer be possible to change the position of the pin. When assembling the piston with the connecting rod and installing the connecting rod and piston group in the cylinder, it is necessary to monitor the correct relative position of the piston and connecting rod and their orientation in the cylinder. There are marks on the piston and connecting rod (arrow on the piston, tide on the connecting rod), which must be directed in the same direction (usually towards the front cover of the engine).
Rice. 55. Pressing the piston pin into the upper head of the connecting rod: a - adaptation; b - pressing process; 1 - fixture roller; 2 - piston pin; 3 - guide; 4 - stop screw; 5 - fixture
When installing the rings on the piston, their locks should not be located in the same plane. This will lead to a significant breakthrough of gases from the combustion chamber into the crankcase. Corner α the relative position of the piston ring locks is determined by the formula α = 360 / n, Where n- the number of rings on the piston. Removal and installation of rings on the piston is carried out using a special tool (Fig. 56).
2. Install the connecting rod and piston groups in the cylinders in accordance with the serial numbers of the cylinders indicated on the piston crowns and on the connecting rods. To install the piston with rings in the cylinder, special devices (crimps) are used (Fig. 57).
Rice. 56. Piston ring remover: 1 - handle; 2 - ledges; 3 - stops; 4 - grips
Rice. 57. Installing the piston in the cylinder
3. Install the crankshaft and liners in the pastels of the block, then install the main bearing caps (Fig. 58). Tightening the caps of the main (and connecting rod) bearings is carried out with a torque wrench (the values of the tightening torques are indicated in the operating manuals for specific car brands). Before installing the crankshaft, clean the connecting rod and main journals, remove burrs at the edges of the holes, wash the shaft and blow compressed air channels for lubrication.
Rice. 58. Installing the crankshaft in the cylinder block
4. Install: connecting rod bearings in the lower head of the connecting rod and its cover; the lower heads of the connecting rods on the connecting rod journals of the crankshaft; covers on the lower heads of the connecting rods (in accordance with the cylinder numbers indicated on both the connecting rod head and on its cover, the covers cannot be interchanged, they are not interchangeable); tighten the fasteners of the covers (Fig. 59).
5. Install the front and rear covers of the unit.
6. Install the flywheel on the crankshaft flange. The crankshaft is balanced at the factory assembly with the flywheel and clutch, therefore, before removing the clutch from the flywheel and the flywheel from the crankshaft flange, it is recommended to put marks on the mating surfaces on which the assembly is reassembled.
Rice. 59. Installation of the lower head of the connecting rod on the neck of the crankshaft
7. Install the oil pan with gasket.
8. Install the block head. Before installing the head, the mating planes of the block and cylinder head are wiped with a clean rag, and the gasket is rubbed with powdered graphite. When installing the head of the block, the nuts (bolts) are tightened with a torque wrench with a certain force (which is indicated in the technical specifications), starting from the center of the head, gradually moving towards the edges (Fig. 60).
9. Install valve cover with gasket.
Rice. 60. Sequence of an inhaling of nuts (bolts) of fastening of a head of cylinders
Gas distribution mechanism repair.
The main malfunctions of the gas distribution mechanism (GRM):
Violation of thermal valve clearances (on engines with adjustable clearance);
Wear of bearings, camshaft cams;
Malfunctions of hydraulic lifters (on engines with automatic clearance adjustment);
Decrease in elasticity and breakage of valve springs;
valve sticking;
Wear and elongation of the chain (belt) of the camshaft drive;
Wear toothed pulley camshaft drive;
Wear of oil deflecting caps, valve stems, guide bushings;
Soot on the valves.
Main timing failure causes- depletion of the established engine resource and, as a result, high wear of structural elements and violation of the rules for operating the engine, including the use of low-quality (liquid), contaminated oil, the use of gasoline with high content tar, prolonged engine operation at maximum speed.
The most serious malfunction of the gas distribution mechanism is stuck valves, which may lead to serious breakdowns engine. There are two reasons for the failure. One is the use of low-quality gasoline, accompanied by the deposition of resins on the valve stems. Another cause is weakened or broken valve springs. In this case, at high engine speeds, the valve does not have time to sit in the “saddle”, it bends and jams (hangs) in the guide sleeve. Fortunately, this error is modern cars is quite rare.
Malfunctions of hydraulic lifters occur when using thin or heavily contaminated oil. The hydraulic compensator ceases to perform its main function - to automatically compensate for gaps in the gas distribution mechanism. Further operation of the engine may lead to jamming of the hydraulic lifters.
Violation thermal gap on engines with adjustable clearance, it can occur due to wear of the bearings and camshaft cams, wear of the camshaft drive gear pulley, and also due to improper adjustment.
Timing malfunctions are quite difficult to diagnose, since similar external signs may correspond to several faults. Often, a specific malfunction is established by direct inspection of the structural elements of the timing with the removal of the cylinder head cover.
Most malfunctions of the gas distribution mechanism lead to violations of the valve timing, at which the engine starts to work unstably and does not develop rated power.
External signs and their corresponding timing failures are listed in Table 2.
table 2
External signs and their corresponding timing malfunctions
| Symptoms | Malfunction |
| Metallic knocking in the cylinder head at low and medium speeds. Reduced engine power | Violation of the thermal gap of the valves. Wear of bearings, camshaft cams |
| · Metallic knocking in the cylinder head on a cold engine. Reduced engine power | Malfunctions of hydraulic lifters |
| · Noise in the camshaft drive area. Silencer shots | · Wear and elongation of the chain (belt) of the camshaft drive. Drive gear wear |
| · Blue smoke from exhaust gases. · Reduced oil level in the engine crankcase. Reduced engine power | · Deterioration of oil deflecting caps, valve stems, guide bushings. KShM malfunction |
| · Loud metallic knocks (detonation knocks) when accelerating the car. Intermittent engine operation | · Soot on the valves. · KShM malfunctions. Poor quality gasoline |
| Short-term dips in the operation of a cold engine. · Reduced engine power. Engine overheating | Decrease in elasticity and breakage of valve springs. valve sticking |
| When the engine is running, pops are heard: in the intake manifold in the muffler | Leakage: intake valve exhaust valve |
| Engine won't start | · The valve timing is broken. Insufficient tightness of valves |
Adjustment of the gas distribution mechanism.
Checking and adjusting the thermal gap between the rocker arm and the end of the valve stem is carried out at an engine temperature of 20-25 ºС in the following sequence.
1. Remove the valve cover.
2. Check and, if necessary, bring the tightening torque of the nuts, fastening the head of the block to the required value.
3. Set the piston of the first cylinder to TDC on the compression stroke (both valves are closed). The piston is installed according to the marks on the crankshaft pulley and cylinder block or using a special locating pin (Fig. 61). Rotating crankshaft ( special key) clockwise, align the alignment mark 1 on the camshaft sprocket with the alignment lug 2 on the camshaft bearing housing. In this case, the fourth cylinder piston is at TDC at the end of the compression stroke and both valves are closed.
Rice. 61. Setting the piston of the first cylinder to TDC on the compression stroke for valve adjustment: 1 - installation mark on the camshaft sprocket; 2 - mounting lug on the camshaft bearing housing
4. Measure the gaps between the rocker arm and the end of the intake and exhaust valves(Fig. 62). The check is carried out with a special metal probe (the thickness of which must correspond to the value of the thermal gap specified in the operating instructions for this brand of car). At the normal clearance value, the feeler gauge should move between the valve and the rocker arm with a slight effort of the hand.
Rice. 62. Checking the thermal gap in the timing: a - timing with roller levers (rockers); b - timing with two-arm levers (rocker arms); 1 - probe; 2 - adjusting screw; 3 - adjusting screw locknut; 4 - rocker; 5 - tip of the pressure screw
5. If necessary, adjust the clearance in the intake and exhaust valves.
Adjustment is carried out in the following sequence:
Loosen the adjusting screw locknut;
Insert a feeler gauge between the valve and the rocker;
Turning the adjusting screw with a key, set the required clearance (at which the probe will move by hand);
While holding the adjusting screw in position, tighten the locknut.
6. Turning the crankshaft each time by an angle α = 720/n(Where n- the number of cylinders of this engine), similarly adjust the valves of the remaining cylinders in accordance with the order of their operation.
7. Install the valve cover, start the engine and listen to the operation of the valve mechanism.
Adjusting the tension of the chain (or belt) of the camshaft drive. Timing operation largely depends on the tension of the chain (or belt) of the camshaft drive, so it is necessary to periodically check and adjust the tension of the chain (belt).
The chain tension is adjusted in the following sequence: loosen the tensioner lock bolt by 1/2 ... 2/3 turns; turn the crankshaft 3 ... 4 turns (in this case, the tensioner will automatically set the required degree of chain tension); tighten the tensioner retaining bolt.
Tension adjustment toothed belt carried out in the following sequence: remove the top protective cover; loosen bracket bolts tension roller and smoothly rotate the crankshaft 2-3 turns (in this case, the bracket spring will automatically set the required belt tension); tighten the bracket mounting bolts and install the protective cover.
The main defects of timing parts and how to eliminate them.
The main defects of the camshaft are bending (beating), wear of the bearing journals and the neck under the camshaft, wear of the cams. If the runout (bending) exceeds allowed values, then the shaft is corrected under pressure or written off. Worn necks are ground to a smaller diameter to one of the repair sizes, and the support bushings are installed with new ones - the repair size. Shaft bearing journals that are out of repair dimensions can be restored by chrome plating or by remaining to the nominal or repair size. A small wear of the cams is eliminated by grinding, and a significant wear is eliminated by surfacing with Sormite No. 1, followed by grinding.
Pushers wear cylindrical and spherical surfaces. Worn pushers are replaced or restored. The cylindrical surface (rod) to the repair size is restored by grinding or chrome plating. In this case, the hole at the guide pushers is processed with a reamer to fit the size of the installed rods or to press in the repair sleeve. The wear of the spherical surface is eliminated by grinding according to the template, maintaining the established specifications height.
In the valve rocker, bushings wear out, which are replaced with new ones, boring a hole in them to a nominal or repair size. Oil holes are drilled in the new bushing. Worn out spherical surface rocker toe is polished.
The main valve defects are wear and burning of the working chamfer, deformation of the plate (head), wear and bending of the rod. When the rod is bent and the disc is deformed, the valve is corrected for special device or replace with a new one. A worn valve stem can be repaired by chrome plating or by refinishing and grinding to nominal size. The worn end of the valve stem is ground to a smooth surface. In case of significant wear or burning of the working chamfer, the valve is replaced with a new one.
Insignificant wear or burning of the working chamfer of the valve is eliminated by grinding it to the seat. Lapping of the valve to the seat is carried out as follows. The timing is disassembled by disconnecting the rocker shaft from the cylinder head, then it is removed complete with rocker arms, racks and other parts. A tool is installed on the cylinder head (Fig. 63) for removing and installing valve springs. After compressing the valve spring, remove the valve cotters and remove the tool from the cylinder head. Released parts are removed from the valve stem (valve springs with a support washer), the valve is removed from the guide sleeve, cleaned of carbon deposits and washed.
Rice. 63. Removal and installation of valve springs with a tool: 1 - fixture A.60311 / R; 2 - mounting board A.60335
For lapping valves, special or self-prepared lapping pastes are used. A thin layer of paste is applied to the valve face, the valve stem is lubricated with clean engine oil and the valve is installed in the seat. With the help of a lapping device or a brace with suction, the valve is given a reciprocating rotational movement. Slightly pressing the valve, turn it 1/3 of a turn, then lift it up, press it again and turn it 1/4 in the opposite direction. Raising the valve periodically, new portions of the paste are applied to the chamfer. Lapping is completed when solid matte belts 1.5-3 mm wide appear on the chamfers of the valve and seat.
After lapping, the valve, seat, channel and guide sleeve are washed with kerosene and wiped dry. The quality of the lapping can be checked before and after the assembly of the valve train. Before Assembly: 15-20 marks are applied across the chamfer with a soft graphite pencil at regular intervals. After inserting the valve into the seat and pressing it firmly, it is turned 1/4 turn. If all the risks are erased, then the quality of grinding is satisfactory. After Assembly: turn the head over and pour kerosene into the combustion chambers. If after 3 minutes no leakage of kerosene is detected, then the quality of grinding is satisfactory.
