>> Repair four-stroke motor scooter.
Repair of a four-stroke scooter motor
As an example, a four-stroke scooter engine is considered. air cooling licensed by Honda, widely used on scooters of Chinese companies (for example, Lifan). The working volume of the engine can be 50, 125 and even 150 cm3. For other models, the design of the main components may be somewhat different, but the basic repair techniques and the tools used differ slightly. Before disassembling the engine itself, it is necessary to remove the plastic casings of the forced air cooling system.
Valve clearance adjustment
About when there is a need for adjustment, which tool should be used and in what sequence all work should be performed, is described in detail in the section on repairing the mokika engine. Differences in the design of the scooter engine are minor. The cylinder head cover must be removed to access the valve train. turning crankshaft by means of a kickstarter or a socket head for the generator rotor (for which there is a hole in its cover), we achieve such a position of the timing chain drive sprocket, in which two marks on the sprocket (in the form of points) grow parallel to the plane of the head connector, and one large hole - perpendicular to them (1). In this position, using a feeler gauge, we (as described in the previous section) measure the gaps in valve mechanism (2).
On a cold engine, the gap should be 0.05 mm for the intake and exhaust valves. If necessary, adjust the clearance as described in section (3).
Removal and installation of a head of the cylinder
We perform work on the engine removed from the scooter, with the carburetor removed and cover removed cylinder heads. The cylinder head is held in place by four nuts on anchor studs that are screwed into the crankcase and pass through the cylinder head. In addition, there are two bolts on the left side of the motor that also pull the cylinder head to the crankcase. We twist four nuts (4) and separate the base of the rocker arms together with the rocker arms and their axles. To loosen the timing chain tension, the chain tensioner must be removed. For the engine under consideration, the timing chain tension during operation is performed automatically. The tensioner housing is located in the upper left part of the engine near the carburetor and is covered with a plastic casing. We unscrew the self-tapping screw for fastening the casing, and then with the “10” key we unscrew the two bolts for fastening the tensioner housing and remove the entire mechanism (see the placement of the mechanism, Fig. 9). We are filming top cover support bearings camshaft located in the cylinder head (5). We extract from the beds of thrust bearings camshaft complete with bearing and drive sprocket (6).
We unscrew the two bolts securing the head to the cylinder with a “10” key. We tap the head and move it up along the studs as if along the guides (7). The junction of the head and cylinder is sealed with a gasket, which is important not to damage.
When reassembling the cylinder head in place, the greatest difficulty is the correct installation of the timing chain sprocket. We drag the chain with a wire through the cavity in the head. We put the chain on the sprocket mounted on the camshaft and place the shaft bearings on their beds in the cylinder head. We install the base of the rocker arms in place together with the rocker arms and their axles. In several stages, we tighten the nuts crosswise, controlling the tightening torques with a torque wrench. Be sure to check the correct installation of the valve timing: it is necessary to combine the marks on the camshaft sprocket and on the head, as well as on the generator rotor and engine crankcase. If you turn the engine crankshaft with mismatched marks, the piston may hit the valves and fail. To see the marks on the generator rotor, it is necessary to remove its casing from right side engine. Turning the crankshaft by the generator rotor, we set the “T” mark opposite the characteristic tide in the form of a horizontally located shelf on the crankcase housing. In this position, the timing marks in the cylinder head must match. If they do not match, the sprocket must be moved one or more links relative to the chain.
Replacement work valve stem seals, lapping or replacing valves do not differ from those described in the section on repairing a mokik engine.
Removal and installation of the cylinder, piston and piston rings
The cylinder is attracted to the crankcase by four studs and two bolts that pass through the cylinder head and through the cylinder itself. If the head is already removed, the cylinder simply slides up on the mounting studs (8).
The general sequence of all work is similar to that described when disassembling the mokika engine. The differences between the scooter engine are in the design features of the tensioner and chain damper.
When installing the cylinder and cylinder head in place, we drag the timing chain with a wire through a special cavity. Mandatory verification of the compliance of the valve timing is described above.
Timing chain replacement
To replace the timing chain in case of excessive stretching (wear) requires almost complete disassembly of the engine and removal of the crankshaft. Special tools (pullers) are required, work without them will lead to breakage of parts. This operation is described in detail in the Mokika engine repair section, the sequence of operations is almost the same.
At reassembly engine, before installing the timing chain in place, it is necessary to “dissolve” the chain tensioner. To do this, unscrew the screw plug on the body of the tensioner mechanism with a wrench, remove the spring (9) from the body and, pressing the tongue with a screwdriver, push the rail all the way. In this form, without installing the spring in place, we mount the tensioner housing. Then we insert the spring and screw the cork back. After a few turns crankshaft made manually, the required timing chain tension will be set automatically.
Removing the rotor and generator windings
This work requires special devices (pullers), work without them will lead to breakage of parts. The sequence of work does not differ from that described in the section on repairing the mokika engine
The only difference is that in the scooter engine, the generator windings are pulled by two bolts to the crankcase, and the ignition system sensor is pulled by the third bolt. We fix the generator rotor (10) with a special device and unscrew the central nut with the end head.
Using a special puller, remove the generator rotor (11), and then unscrew the fastening bolts and remove the generator rotor together with the ignition system sensor. Mounting the generator on regular place produce in reverse order.
Removing the variator clutch
We unscrew the eight bolts securing the left crankcase cover with the “8” key and remove it together with the kickstarter lever (12). We remove the overrunning clutch assembly of the electric starter from the crankcase. We fix the drive pulley of the variator with a special device. Using the “17” wrench, unscrew the nut securing the pulley to the left crankshaft journal (13). The locking device must be rated for a significant tightening torque. We remove the plastic impeller of the variator with the kickstarter ratchet. Light blows we press the drive half-pulley of the variator (which is also the drive gear of the electric starter) from the splines of the crankshaft neck. We remove the variator belt, the drive pulley bushing and the movable variator half-pulley assembly with weights. Installation of parts in a regular place is carried out in reverse order.
Removal and installation of the crankshaft
This operation is carried out to replace the timing chain, replace the bearing shaft, seals (oil seals) or the entire shaft. For disassembly, special tools (pullers) are required; work without them will lead to breakage of parts. To remove the crankshaft, it is necessary to dismantle the cylinder head and the cylinder itself, as well as the generator rotor and the variator clutch located on the crankshaft journals. We unscrew the eight bolts securing the right crankcase cover with a tubular wrench (these bolts also fasten the crankcase halves together) and remove the cover (14) and the cardboard gasket. The oil pump drive is located under the cover. We remove the plastic gear of the nose drive, unscrew one more bolt that fastens the crankcase halves, and separate the right half of the crankcase. When pressing out the crankshaft, it is forbidden to hit the pins with hard objects. With light blows of a wooden or rubber mallet on the trunnion of the crankshaft, we press out the shaft together with the bearings (15). If necessary, the crankshaft bearings must be replaced.
We install the crankshaft in the reverse order. Before installing the crankshaft bearings, the separator cavities must be lubricated with engine oil. When assembling, set new gasket between the crankcase halves.
Sooner or later, during the operation of the scooter, the owner is faced with the need to replace any parts. This is not about standard consumables such as candles or seals. Replacing the timing chain of a scooter is quite within the power of its owner, this article will help.
How to know if a replacement is needed
It is clear that it is necessary to change the circuit when there is its frank dysfunction. When worn, the chain makes a rumble. Well, or jumped over the star's tooth. Or flew off, which indicates its stretching and wear.
Standard chain life should be close to the life of the scooter engine itself. It is logical. Each owner operates vehicle in different ways, but the average life of the chain is somewhere around 15,000-18,000 km. In a situation where they cut the engine in half to eliminate other malfunctions, and immediately replaced the chain when it was used for, for example, 9000 km, everything is clear.
There are options for shortening the chain when stretched. But there are some reservations: if the step does not match, the star begins to fade, i.e. a stretched chain eats a camshaft star. If the wear of the star is small, you can isolate the link and ride a little. You need to do this correctly, adjusting the chain tension with a tensioner, and not forcibly. Otherwise, ruin the chain completely.
What is characteristic of a worn chain
A small point: to check, you need to remove it. The degree of wear can be assessed by the angle of horizontal deflection. If it sags down, leaving almost vertically - change 100%. The new chain deviates approximately 45 degrees from the horizontal.
And laying out the old and new chains on the surface, you can see that the first one will be longer. Also, the wear of the timing chain of the scooter can be indirectly judged by the level of extension of the tensioner rod. Critical wear is when the stem is fully extended.
How to replace the timing chain in the engine
Having decided on such an action as replacing the timing chain of a scooter, you need to decide on the method for implementing the plan.
There are two replacement options:
- With a thorough disassembly of the scooter engine
- No engine disassembly.
How to change, everyone decides for himself. Both methods, advantages and disadvantages are described in detail below.
With disassembly
Should be picked up the right tools- generator and variator pullers (you can make them yourself), a kickstarter sprocket puller, heads for 8, 10, 12 and 17 mm, a hammer, two screwdrivers (flat, Phillips).
The engine is removed from its place, the oil is poured out, all parts are wiped and cleaned. Next, remove the muffler and cooling cover. We remove the generator only with a puller. To do this, unscrew the bolts from the impeller, remove it from the rotor. It is necessary to fix the rotor with a puller and unscrew the nut. Then we tear off the rotor from the crankshaft trunnion. Remove the variator cover. Also fix the impeller with a puller, unscrew the nut, remove the variator from the axle.
Under the variator is the kickstarter gear. Similarly, a puller is required for it. Then we clean the cylinder connectors, valve covers and block heads. Unscrew the bolts on the valve covers, remove it. Next, remove the scooter timing chain tensioner. Having unscrewed the bolts on the cylinder head, we take out the camshaft bed.
Next, remove the chain from the camshaft, and pull it out of bed. In order not to lose the guide bushings that center the parts relative to each other, they must be removed and removed. We remove the cylinder head, the cylinder itself, the piston (to do this, pull out the retaining ring and pin from the upper connecting rod head).
After unscrewing the bolts on the crankcase cover, tapping it a little, remove it from the engine. We take out the intermediate gear of the starter, with a screwdriver and a hammer turn off the overrunning clutch nut (clockwise) and remove the gear and housing from the trunnion. We got to the circuit!
Put away protective screen from the oil pump. Putting a metal stick under the chain, turning the nut on the oil pump sprocket, remove it and remove the chain.
Without disassembly
We take the following tools: a Phillips screwdriver, pliers, new chain and a special puller. More about him will be below. We expand the new chain - for this, we press the pin out of the articulation of the links with a puller, but not completely.
A little about the shooter
It's called the timing chain puller. It can be made by a turner, turning a threaded extruding finger, rolling into it a strong pin with a diameter like that of a chain pin. You can buy a ready-made, bicycle. Just slightly narrow the pin to the desired size.
Remove the cooling casing from the scooter engine, then the cylinder head cover. Next, you need to remove the chain tensioner. We remove the camshaft bed, take out the shaft, remove the star.
We take the puller, center it with the pin, gradually squeeze out the pin. You can press it out completely, it will not be useful. We compare the links of the new and old chains, in seat pin we pull the wire and fix the ends of both chains. We scroll by the cooling impeller counterclockwise, gradually replacing the old circuit with a new one.
Then we disconnect the ends of the chains, throw out the old one, and combine new links from the ends. We check the alignment, install the pin, gently press the pin with pliers so as not to damage the new chain. We first check the mobility of the links. We finish the pin with a puller finally. Again, we control mobility. This moment is very important: if you install the pin unevenly, lubricate it, it will begin to rest against one of the links, and squeeze out the next one.
As a result, the subsequent pin or link is bent, leading to its jamming and immobility.
Next, we assemble the engine in the reverse order, setting the marks on the rotor. When setting the camshaft bed, after tightening the nuts, you need to check the valve clearances with a feeler gauge. Upper valve - inlet: 0.05mm, lower - outlet: - 0.1. The feeler gauge must pass freely between the valve and the adjusting screw.
Then install the chain tensioner. We unscrew the bolt on the tensioner from above, install the screwdriver in the groove, and, turning it, push the rod back. Everything else is fixed back according to the scheme.
Which method is preferable
It is logical that the first option with a complete disassembly of the scooter engine is more “confused”, takes more time and effort. But it seems to be more reliable. Firstly, the factory integrity of the circuit is not violated; secondly, when disassembling the scooter engine, you can see any shortcomings, such as cracks, wear, change seals, clean parts.
The second option is more simplified, can be used when you only need to replace the chain. And you are confident in the quality of your work.
Final word
Scooter- a fairly popular vehicle, is in ever-increasing demand. Because it leaves traffic jams behind, has low operating costs and is economical in terms of fuel and lubricants. Many people prefer to do scooter repairs on their own, especially since four-stroke engines simple and reliable in execution. Timely inspections, careful operation and the above article will allow you to enjoy riding this miracle of the Asian motorcycle industry for a long time to come.
1. Put the timing chain on the crankshaft, install the chain tensioner shoe (if removed). Lubricate the chain with oil before installation!
2. Heat the bearing seat on the left half of the crankcase with a blowtorch. Insert the crankshaft together with the bearing into the left half of the crankcase. Fitting the bearing to the crankshaft should be effortless and can simply be done with one hand. The side of the crankshaft on which the variator will be put on must be inserted into the left half of the crankcase! Pay attention to this so as not to accidentally confuse! In the figure, the side for the variator is marked with a red arrow. It is necessary to put the bearing in place carefully so that there is no distortion during the fit. After the fit is completed, carefully inspect the bearing seat. The bearing must sit without distortion. The distance from the edge of the walls of the bearing seat and the edges of the bearing along the perimeter must be the same! The bearing should be deepened into the seat so that from its upper edge to the edge of the seat the distance is about 1 mm. If the bearing does not fit correctly, it is necessary to heat the bearing seat and remove it as described earlier. Then repeat the installation again. If the bearing is distorted during landing, this will lead to a quick breakdown of the CPG.
5. Heat the bearing seat on the right half of the crankcase. Connect the right half of the crankcase to the crankshaft and crankshaft bearing. The connection should be effortless. The half of the crankcase must be seated with both hands, in order to avoid distortion, which will prevent the bearing from easily entering the seat. If the bearing is incorrectly seated, there will be a misalignment, which will lead to breakdown of the CPG. Control of normal fit - the edges of the crankshaft halves must converge exactly, without distortions, at the same distance around the entire perimeter. If it turns out to be skewed, remove the right half of the crankcase, as described earlier, and repeat everything again.
6. If the right half of the crankcase is seated successfully, immediately connect the crankcase halves with a tie bolt.
7. Install oil pump with gears: Connect oil pump and pucks. Attention! There is a mark on the pump ("arrow up"). When installing the pump, it is necessary that the arrow “looks” up. Attach the oil pump drive gear.
8. Install the right crankcase cover (with a feeler gauge), tighten the crankcase with bolts, tightening them evenly to avoid distortion of the halves. Check the connection by the distance between the crankcase halves along their entire perimeter. The distance must always be the same!
9. After connecting the halves of the crankcase, remove excess sealant that has come out with a rag.
10. After assembly, cover the crankcase with a clean rag to prevent accidental entry of small parts inside. We should not forget that it is recommended to install new crankshaft oil seals, even if the old ones are still serviceable.
11. Install the parts of the variator drive pulley (4,5,6) assembled together (carefully so that the rollers do not spill out of their grooves). Insert bushing (7).
12. Insert the electric starter bendix into place.
13. Put on the belt, install the fixed cheek of the variator (3), install the cooling element (2) with the kickstarter washer (1) on the fixed cheek of the variator (3). Tighten the fixing nut.
14. Holding stopper toothed pulley variator, tighten the nut securing the variator to the crankshaft.
16. Raise, by rotating the rotor (magnet) of the generator, the connecting rod to the TDC position (upper dead center). Always turn the crankshaft only in the clockwise direction when viewed from the generator!
17. Take the rotor (magnet) of the generator with both hands and put it on the crankshaft. Don't forget to insert the dowel! Be careful, remembering that this is a magnet, and he tries to "jump off to the side" due to the action of magnetic fields. Attention! To set the ignition timing correctly, it is necessary to install the rotor (magnet) of the generator so that the mark on it is located as shown in the figure above.
18. Using a puller, fix the rotor (magnet) of the generator and tighten the nut that secures it to the crankshaft.
19. With tool for removal and installation piston rings(or by hand) put the rings on the piston. Wear rubber gloves to prevent debris from getting under the rings (or with clean hands). If debris gets under the rings, the cylinder mirror will be damaged, which will further lead to serious damage to the CPG. Rings must be put on only through the top of the piston! Start installing rings from the bottom oil scraper ring. To facilitate the work, use the universal lubricant spray WD-40.
20. Raise, rotating by hand the rotor (magnet) of the generator, the connecting rod to the TDC position ( top dead points). Always turn the crankshaft only in the clockwise direction when viewed from the alternator side! Move the crankshaft connecting rod and with the piston forward in the direction of travel of the scooter.
21. Put the piston on the crankshaft connecting rod. Note! On the top of the piston there is a factory label "IN" (English - "input"). Putting the piston on the connecting rod, it is necessary to position the piston so that the side with the “IN” mark is located in the direction of the carburetor.
22. Carefully insert into the piston piston pin. In this case, it is necessary to firmly hold the piston with your hand to prevent it from fluctuating “left-right”. Otherwise, it will damage the connection in the lower head of the crankshaft connecting rod.
23. Insert two circlips into the piston. Insert the retaining ring with its end not twisted inward into the recess inside the piston. Use round-nose pliers to take the retaining ring by its end in the center. Gently "screw" the retaining ring inward. Will check it out correct installation- the retaining ring must, rotating inside, not get out of the seat.
24. Put a new gasket between the cylinder and the crankcase (usually made from paronite). Install the cylinder, carefully, one by one, inserting the rings into the cylinder. Do not forget about the timing chain - it also needs to be carefully threaded through the cylinder wall. Before putting the cylinder on the piston, lubricate the cylinder mirror and piston with rings with engine oil.
Raise the piston to TDC, holding the cylinder with one hand and rotating the bell (magnet) of the generator with the other, it is imperative that the mark on the generator magnet with the letter "T" is set opposite the flag (protrusion on the crankcase) and at the same time the piston is at TDC.
26. Install a gasket between the cylinder and the cylinder head (this gasket is usually made of metal).
27. Put the cylinder head on the studs.
28. Put the timing camshaft on the cylinder head so that the position of the flywheel of the timing camshaft becomes as shown in the photo, i.e. the larger hole on the camshaft sprocket should be directed towards the valve head cover, and the two smaller ones should be in a parallel line with the valve cover split plane, put the timing chain on the sprocket, holding the shaft in this position. Thus, it is set correct position camshaft and, accordingly, the correctness of the valve timing of the scooter engine. Please note that sometimes it is enough to jump the timing chains by one tooth of the timing shaft sprocket - the scooter engine will not be able to start.
29. Connect the camshaft seat with the fingers and rockers (rocker arms).
30. Install the camshaft seat on the camshaft, taking into account the indication of the side where the exhaust rocker (rocker arm) is located. Be careful! On the top of the camshaft seat there is a factory label "EX" (English - "exit"). This is the graduation rocker mark.
31. Fasten the camshaft seat, cylinder head and cylinder with nuts, and also tighten the cylinder and head with the engine crankcase with two long bolts. Tighten alternately increasing the tightening force on each nut and bolt to evenly distribute the tightening torque of the CPG surfaces.
It's always like this in life: one thing is good, the other is bad. Exactly the same principle is the case with various kinds of mechanical torque transmissions. The chain drive is no exception here. On the one hand, there is nothing simpler, more reliable, lighter, more compact and cheaper than a chain drive.
And on the other hand, we get the eternal "haemorrhoids" with stretching the chain, wear of the sprockets, endless cleaning, lubrication, maintenance and stretching of this very chain. But there is nothing to do, the chain transmission has a lot of advantages over other types mechanical gears Therefore, these types of transmissions are used almost everywhere.
However, today we will not talk about a chain drive as such, but about a method for diagnosing a timing chain that drives a scooter engine camshaft.
To change or not to change?
Suppose you “capitalize” your engine: you change oil seals, crankshaft, gaskets and other devices, but you doubt whether to change the timing chain to a new one or not. In vain doubt - change it to a new one as soon as possible. And now I will explain why.
See for yourself: the chain has an average life of about 18,000-20,000 km of scooter run ( personal experience), about the same as the average life of the engine itself. And you, for example, after a run of 6,000 km, the crankshaft jammed or the engine dripped, or something else happened that required complete disassembly engine. You naturally disassemble the engine, change the crankshaft to a new one, and leave the chain, which by that time had exhausted a third of its resource.
And what happens? The chain, after 12,000 km, will run out of its resource and become unusable, and the crankshaft and other parts will be in good condition and you like it or not, you will have to again, because of the chain alone, to half the engine. Is it necessary? The chain is a consumable. Never skimp on it!
Examination
Personally, I never check timing chains. I just throw them in the trash, no matter how awesome they seem to me. The chain for me is a consumable, the same as a candle, oil or an oil seal. But if it’s important for you, or it’s stressful for money, you can use the old grandfather way.
We stretch the chain along the length, clamp it with our fingers and try to position it in a horizontal position
- If the chain has described an arc that looks very much like an angle of 90 degrees, then feel free to throw it in the trash
- If the chain is slightly bent and described a small arc, then such a chain is quite suitable for further operation.
For clarity, I took a new and heavily worn chain, put them together and checked for horizontal deflection. As you can see: the new chain (above) described a slightly noticeable arc, and the worn-out and useless chain sagged like snot, almost at an angle of 90 degrees.
The worn chain was about a centimeter longer than the new one.
How to replace the timing chain of a scooter engine?
Very simple, my friends: remove the engine from the frame, disassemble it and change the chain to a new one. There are no special secrets in this matter, just as there are no special ways to “cheat fate” and replace the chain without disassembling the engine. The chain can only be replaced by completely disassembling the engine.
There is, of course, one YouTube guy who rivets an old chain, then rivets a new one, connects both chains, pulls the old one, winds a new one, and then rivets the whole thing back, but this is porn. I don’t suffer from such crap, since the result of such a “repair” is not always predictable.
The timing chain is in no way designed to be riveted or riveted. It can easily be led or twisted in the process of riveting-riveting, and this is a sure way to ensure that the chain will fly off the sprocket while the engine is running, and then, with luck ... Maybe everything will work out, or maybe bend the valves. And one more thing: it will be beyond the power of a beginner to rivet a chain with high quality. This work is not as simple as it might seem at first glance. Therefore, — do not suffer garbage, and disassemble the engine.
How to adjust, tension the chain?
Yes, you can’t stretch it and adjust it, and you don’t hammer the Google or Yandex search with such requests. The chain in the scooter's engine is tensioned automatically. And if you have it already stretched to such an extent that it starts to fly off or jump over the teeth - feel free to disassemble the engine and change it to a new one. Miracles don't happen.
And I will prove it to you now. The chain in the engine is tensioned using a special tensioner that operates in full automatic mode. As the chain stretches, the tensioner rod, under the action of an internal spring, exits the housing and tightens the chain. And the more the chain is stretched, the more the rod will come out. But! The rod has a limited stroke: on a completely new chain, it comes out about a third of its stroke and then, as it stretches, it comes out completely and then it will not come out any more. Therefore, the chain will no longer be stretched! And all your attempts to correct the situation will lead to nothing.
Modern engines of imported motorcycles require almost no attention, well, perhaps timely replacement oils and filters. But motorcycles with quite high mileage, there comes a moment when the engine itself tells the increased ones that it is time to deal with the maintenance of the timing system - the gas distribution mechanism. How to do it correctly without harming your engine, we will consider in this article.
Unlike modern automobile motors, (ancient Zhiguli and Muscovites do not count), (and Italian exclusives, such as Ducati motorcycles), where the gas distribution mechanism is controlled by a rubber toothed belt, on most modern imported motorcycles, the timing chain is in command. Of course, there are exceptions on some cruisers of large cubic capacity, or English classic motorcycles where a camshaft drive is used using gears. But such a drive does not need to be adjusted at all, because if, after a very long run, parts wear out, they simply change with new ones (the same gears).
With a chain, everything is not as simple as it seems, since it must be constantly tensioned with a certain force in order to accurately transmit torque and last the prescribed period. After all, the camshaft of any engine must rotate absolutely synchronously with the crankshaft. And if there is a slight lag or advance even by 1 -1.5 °, then the engine of your motorcycle will lose its power, and the wear of the timing parts will increase. If the lag or advance increases by several degrees, then it is quite likely that the pistons will meet the valves, and this is already very serious. In most cases, destruction of many parts of the gas distribution mechanism will occur, and most likely it will be easier to replace the entire engine head.
I think many have understood the importance of the chain tension system, now it remains to understand all this in more detail. To tension the chain with a certain force, a set of parts designed for this is used, consisting in most cases of two dampers coated with anti-friction material, along which the chain slides during operation, and the chain tensioner itself. The tensioner is mounted in the engine so as to rest against the driven arm of the chain, and constantly press this arm with the required force. This entire node (and its normal work) is very important, since the failure of this node is dangerous and can lead to the sad consequences described above. And although problems here happen quite rarely, it still deserves attention, since in order to correctly diagnose tensioner parts and then assemble them correctly, you need to know how this unit works.
There are several designs of tensioners, depending on the years of manufacture. On the most ancient models until the 80s, simple mechanical timing tensioners were installed (see photo on the left), which were very easy to set up. It was only necessary to loosen the coupling bolt (usually a 10 key), then, in the course of rotation, turn the engine crankshaft until the resistance weakens, and re-tighten the bolt. Everything is pretty fast and simple.
But after the 80th year, tensioners began to appear, automatically tightening the chain, relative to its stretching. They are still in use today. Some systems of automatic tensioners are slightly different from each other, but their essence is the same - if they once advanced to the required distance, then the tensioner rod is fixed in this position and will not be able to move back. Due to this, the timing chain is always constantly tensioned with a certain force, which is set by the tensioner spring.
But many will ask the question: why climb into the tension system, if everything is automated there. Well, firstly, after all, I already said at the very beginning of the article that you only have to climb into this knot on motorcycles with high mileage, because at a certain mileage everything wears out sometime. And secondly, when disassembling the motor (for example, to repair it), or replacing tensioner parts, many novice repairmen make mistakes that can end up being very expensive. My goal, or rather the goal of this article, is to warn against these mistakes.
One of the common mistakes of beginner “masters” is when, when removing the valve cover of some engines, on which the damper is located, the chain will naturally weaken, since the damper is no longer pressed, the cover is dismantled. And when the chain tension is loosened, a serviceable tensioner will immediately pull the chain slightly forward. The novice “master”, after checking the chain tension, will naturally be delighted with the normal tension. Just now install valve cover he will not succeed in place normally, since the damper located in the lid will rest against a stretched chain. Woe mechanic begins to push harder on the cover and compress it with regular bolts.
Slightly worn chain guide against which the tensioner rod rests. With a strong tension of the chain, it can be erased in a few minutes of operation.
As a result, either the tensioner latch breaks, or the tensioner shoe (or damper) itself breaks. If the quality parts of the tensioner and damper withstand such abuse, then the next time the engine is started, the chain will be so tight that the friction material of the tensioner and damper will be erased in a few minutes of operation. And the chain itself, in the same short time of operation, will stretch as if high mileage. As a result, the wear and noise of this unit will increase many times, and very quickly. Therefore, before assembling the assembly, I advise you to study the principle of operation of the tensioner of your particular engine, and find a way to return the tensioner rod back. Below I will show you how to do it right.
The sprocket of a modern silent chain looks like a gear.
1 - sprocket, 2 - additional gear motor transmission, 3 - main gear, 4 - damper springs.
As a rule, with high mileage, the timing chain stretches and starts to ring. In most cases, to eliminate this defect, it is necessary to replace the chain, and the dampers too. But many novice "mechanics" by placing one or more washers under the tensioner spring think that they have solved the problem. But this helper does not help for a very long time, or does not help at all. After all, the asterisk of a modern silent chain looks like a gear. The modern silent chain (see photo) is designed in such a way that, unlike a conventional chain, it covers the tooth with a much larger link area. When any chain is pulled out, increased gaps appear between the sprocket tooth and the link, which cannot be fixed by anything, the link is pulled out, and the distance between the axes (pins) of the link increases, wear is wear. From this comes increased noise, but this is half the trouble.
If you add all the increased clearances of each chain link together, you get a significant lag behind the camshaft from the crankshaft. The motor loses some of its power, because the gas distribution phases begin to lag. For your information: if the chain has 114 - 116 hinges (links) - depending on the type of engine, then the wear of each of these hinges is only 0.08 mm, as if adding to overall length the chains are another link, and from this the sprockets of the timing drives, the ignition, are shifted back in phase from the sprocket on the crankshaft, by a whole chain link! As a result, the power characteristics and economic performance of the engine are significantly reduced. Now imagine that if the links wear out not by 0.08 mm, but more, how will the engine start to work then? The conclusion suggests itself - an elongated motor chain will no longer be able to transfer rotation from the crankshaft to the camshaft normally and in a timely manner.
A modern silent motor chain, the links of which almost completely cover the sprocket teeth.
From all of the above, we will understand for ourselves that only a new chain can return the motor to its former strength, and if the friction material of the tensioner and damper is worn out, then their replacement is also extremely necessary. Inspect the chain sprockets as well, they should not show signs of wear visible to the naked eye. And if, with the tensioner mechanism assembled and the chain in place, your tensioner stem is fully extended, then your bike's motor chain is fully extended, and it is time to replace it with a new one.
To replace the chain without removing the sprockets, it must be pressed out, and then the new chain must be pulled through and pressed in with special device. How to properly stretch a new chain, and about the device for pressing the chain itself, I advise you to read here
Still, consider some types of tensioners A little more detail, as I think it will be useful for beginner mechanics.
1 - spring stub screw, 2 - tensioner body, 3 - spring-loaded stopper of the ratchet rail, 4 - rail itself, 5 - spring, 6 - plug sealing washer. The red arrow shows the place of pressure to pull the latch and then drown the pusher rod.
Rack tensioner. This is one of the ancient mechanical tensioners, but already working on the machine (and not from key adjustment, as I described above). It is quite reliable, and does not require attention for quite a long time. The main working element of this type of tensioner is the pusher. It is constantly pressed by a spring in the direction of chain tension, and an ordinary ratchet mechanism does not allow the pusher to return in the opposite direction (yes, no back). The ratchet mechanism is very simple and is a spring-loaded stopper resting against a gear rack.
After removing the tensioner from the engine, the pusher on a working unit should fully extend outward, and if you try to push it out even more with your hands, it means that the spring has sagged and needs to be replaced. Well, if, when trying to push the pusher inward, on the contrary, you managed to do it, then the ratchet mechanism of the ratchet is faulty (the teeth are broken or worn out). Naturally, you need to replace such a part with a new one.
Before installing such a tensioner back on the engine, inspect all parts for wear, and if there are no visible signs of wear and jamming of the mechanism, then you can install it back on the engine. To do this, unscrew the spring plug 1 from the tensioner housing (see photo above), and then pulling the spring-loaded stopper from the rack teeth (for example, with a thin screwdriver or a finger as in the photo on the left), now you can drown the pusher back (since you pull the latch with a screwdriver or a finger and it does not interfere). Well, after you fix the pusher itself with screws on your engine, you can install the spring back and compress it with a screw plug 1.
1 - plug bolt, 2 - screw tensioner housing, 3 - pusher itself.
Screw tensioner. On more modern motorcycle engines, a screw tensioner is installed, which, unlike the rack and pinion described above, adjusts the spring tension more smoothly due to the rotation of the screw, which smoothly extends the pusher. And the thread of a special screw does not allow the pusher to move back into the body. You can check the correct operation of such a tensioner as follows. Having unscrewed the plug screw from the pusher housing, and then inserting a thin screwdriver into the housing and feeling for the screw with it, turn it, while the pusher will begin to slide into the housing (the pusher should not move outward or inward, the play of the pusher should not be felt either). Then try to loosen the screw (remove the screwdriver), and at this moment the pusher should quickly pop out with a click until it stops. When turning the screw with a screwdriver, you should only feel the tension of the compressible spring, and the screw itself should turn easily and without jamming.
In the same way, such a tensioner is installed back on the engine, that is, we turn the screw with a screwdriver until the pusher enters the housing completely, then holding the screw in this position with a screwdriver, with the help of an assistant, try to install the tensioner in place on the motor, tighten the bolts securing it, and only then release the screwdriver. It remains to tighten the screw cap.
1 - cover-plug of the wedge spring, 2 - tensioner housing, 3 - wedge, 4 - wedge spring, 5 - pusher spring, 6 - limiter bolt, 7 - limiter bolt groove, 8 - pusher. The broken cover is shown in red.
wedge tensioner. Tensioner motor circuit Timing belt with wedge tensioner, rarely installed on motorcycle engines but still worth writing about. Such a tensioner is not as compact as the mechanisms described above, but it is unrealistic to break it, since it has neither small teeth, nor fine and delicate threads. The tension of the motor chain is also smoothly adjustable as on a screw tensioner. The pusher itself is pushed forward by a spring, and a special stopper bolt, which presses on the groove in the pusher, fixes it from unnecessary movement (see photo). And the wedge, which is constantly pressed by the spring, does not allow the pusher to return back to the body.
After examining the details of the tensioner for professional suitability, and not finding visible signs of wear, play of the pusher and jamming, you can return the tensioner back to the engine. But before that, it is necessary to drown the pusher, and for this it is necessary to unscrew the spring support cover, then remove the spring, and only after that it will be possible to remove the wedge that prevents the tensioner rod from sliding back into the housing. With the chain tensioner in place on the engine, now calmly insert the wedge and spring into place, and then screw on the cover, which will compress the spring and wedge.
Hydraulic timing chain tensioner mounted on the motor. Connected to it is a tube oil system of this engine.
hydraulic tensioner. They are also called oil tensioners, as they work from the pressure of the oil that enters the inside of the hydraulic cylinder from the engine lubrication system. Such tensioners have long been used on many cars, and on motorcycles they began to be used in last years, and then not so often. They are mainly used on quiet engines, since on forced engines the oil pressure can vary widely, and this will change the chain tension, naturally this is not good.
Moreover, for the normal and accurate operation of such a system, a very clean and high-quality engine oil, because inside the tensioner there is a plunger made with high precision and with a very small gap in the hydraulic tensioner cylinder. And if even the slightest speck gets into this pair (plunger and cylinder) with oil, then the plunger with the tensioner rod will simply jam. The consequences are very sad, since no matter how much oil pressure is in the system, it will no longer be able to push the jammed plunger and chain tensioner rod. This will weaken the chain and the timing will no longer work normally. Therefore, the purity of the oil and its timely replacement plays a huge role here.
Hydraulic timing chain tensioner removed from the engine. The polished push rod is visible.
Moreover, in cold weather, or after long parking(when the oil drains into the sump), engines with a hydraulic tensioner, jingle the chain for a few seconds of engine operation (until the oil fills the hydraulic cylinder to required pressure). At this point, the main thing is not to increase the speed of your engine until the sound disappears. However, I do not advise you to increase the speed on any motor until it warms up.
There is also an automatic tensioner as in the photo on the left, in which, before installing it on the engine, you just need to cock the spring-loaded handwheel (turn the wheel) and drown the tensioner push rod. After installing such a tensioner on your engine, we turn the wheel back, and the pusher rod, when released, will extend and tension the chain.
Remember that if on any type of tensioner, the pushrod is pushed out as far as possible, then your bike's motor timing chain is fully extended (worn out). The wear of parts such as the friction material (sled) of dampers is usually visible visually. Naturally worn or loose parts must be replaced with new ones.
If you have overhauled the engine proper repair Japanese four-stroke, you can), then after assembling it, install the motor chain tensioner last, and as described above - with a completely recessed pusher. After installing the tensioner on the engine, turn the crankshaft in the direction of rotation (for the crankshaft bolt). assembled engine 4-5 turns, and at the same time make sure that the friction shoe of the tensioner takes its working position. Do not try to do the same operation by rotating the camshaft instead of the crankshaft.
I hope now you will be able to service the timing of an imported motorcycle more competently, and, most importantly, to diagnose this unit and diagnose parts on your own, because you can only dream of a high-quality motorcycle service, especially in the outback. Good luck everyone!.
