How to Install a Piston On a Grass Trimmer
How to correctly install the piston on a trimmer
Replacing the piston group in a chainsaw or trimmer
Repair of such level should always be weighed. How to properly install the rings on the piston of a two-stroke In the installation of rings on the piston. In these small engines operating at elevated speeds, the substitution of the 1st piston that has burned out or jammed, does not give the long result and as the need to change the entire piston group. You should therefore think about whether you want to keep using this saw or buy a new one.
If it is a professional model, such repair is worthwhile, but if it is an old domestic model such as Husqvarna 40 and it has worked for more than ten or twelve years, it is not profitable to repair it. Because it’s going to cost that much to repair. as well as the purchase of a new saw, albeit not Husqvarna, but the PARTNER P350XT CHROME, worth 165 will suffice. over, the company Husqvarna sells such saws, because PARTNER is a subsidiary of the company.
But if you did decide to repair your chainsaw or grass trimmer, then you need original spare parts, which are not cheap. If the engine is used properly, the first repair may not come soon and you will only have to replace the piston ring or rings, depending on the model. But if the saw jammed you need to change the whole piston group. cylinder, piston and rings.
It should be noted that chainsaws Husqvarna 136/141 have approximately 500-600 hours service life, Husqvarna 340/350. 1000-1200 hours, professional chainsaws at least 2000-2500 hours, subject to strict compliance with the instruction manual. In fact, you can not rely on these figures, because the actual life can vary significantly up and down. But it’s possible to say approximately that semi-professional saws work 3-4 times longer then amateur ones, and professional ones up to 10 times longer and more.
Of course, nothing is eternal, but it is one thing if you change the piston group after many years of operation and it worked out its motor-hours, fully paid for itself, and another thing is that the saw filled up for example with one gasoline, no oil, and it jammed. Such saw has to be repaired as all other parts are normal.
Many companies deliberately inflate the cost of spare parts to buy new models. STIHL chain saws and grass trimmers, for example, have more spare parts than the Husqvarna. So when choosing a certain model get to know about the spare parts. RVT
How to install the rings on the piston of a two strokes scooter correctly
In the installation of the rings on the piston of a two-stroke scooter or a four-stroke, there is nothing complicated, and many people know it. But most scooters, who have just recently purchased such a technique, have no idea even how to replace the piston on a scooter, how to properly install the rings on the piston, where the arrow on the piston should look and much more. In this lesson, I will tell you how to put the rings on the piston and reassemble the piston. Since we already talked about 4 stroke engines, here we’ll talk about 2 stroke engines only.So, our piston is worn out and needs to be replaced. It’s the rings and the piston that wear out first, and they’re usually the only ones you have to change. If the piston is heavily worn, it is necessary to re-bore the cylinder. It is also being cut if the piston is jammed in the cylinder, creating deep scratches on the cylinder walls. There is nothing wrong with it, and if your new cylinder passed the correct boring (for which you will need to pay only about 10), it already needs a repair set of rings with a new piston. Such rings are designated by the marking 0.25. The second bore is respectively 0.5 and t.д. to one. After buying a piston, it needs to be assembled. In the kit, as a rule, you will find the piston itself, two compression rings, a third thin crimp ring (about its purpose below), piston pin and two piston pin retaining rings
How to change the piston on the trimmer.
In this video I will show you how to change the piston on the trimmer. How to properly install rings on a two-stroke scooter piston Published 25.08 I will change it on the trimmer.
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How to put the piston
Pridonok shows and tells how to install the piston correctly
In the cylinder on a scooter and motorcycle Now for the third ring in the kit. Its purpose. to spring the lower compression ring. It sets it under him actually, and usually does not bear any usefulness in operation. You can put or throw away this ring, it makes no difference. Many piston manufacturers do not have it included at all. It’s time to put everything back together. Depending on the scooter model, the compression rings may be the same or vary in thickness and cross section. Most Honda scooter pistons, for example, have different rings, where the top is thinner than the bottom and has a different cross section.
Make sure you pay attention to this when installing, the top one is thinner and beveled at an angle.
Also pay attention to the inscription on the ring (usually the letter T or repair size), the inscription should always be on top, that is opposite of the pin. First you need to put on the lower one, then the upper one. They do not need to be stretched and bent. These manipulations should be carried out carefully.
There are locks in the grooves for the rings, which prevent the rotation of the rings during operation, so the ring gap must be exactly in these locks, otherwise you will not stick the piston into the cylinder.
And the last important point is the arrow (1) on the bottom of the piston or the EX inscription. Both the arrow and the lettering must point towards the exhaust (2). In this case, the rings’ locks will be on the petal valve’s side. If the locks are placed towards the exhaust, the piston will not last long, the rings will be pulled into the exhaust window and gradually wear it down.
At all manipulations with the piston, it is necessary to put a rag into a window of a crankcase, that anything did not get there casually, a crankshaft with bearings we still need.
When installing the piston pin, pay attention to the condition of the cage (bearing), it may need to be replaced. Before installing the piston pin, install the retaining ring on one side before installing the piston (usually on the side where you will not be comfortable with the pin and the second retaining ring). Then put the pin with the bearing and the second retaining ring, it will make a definite click when it locks in the groove.
That’s all, now put the cylinder, not the piston (not forgetting to check the condition of the gaskets and lubricate the piston and the walls of the cylinder with motor oil), the cylinder head and tighten the bolts alternately in a crosswise order.
Tip for fixing your MTD-600 trimmer.
Today I want to share some useful information about grass trimmer repair, which was kindly provided to me by our reader Yuri. With his permission, I publish this, in my opinion, very useful information.
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I will share how I repaired the trimmer for grass MTD-600 (problems with ignition), maybe someone will help.
At first nothing is clear, grass trimmer just does not start, not even sneezes.
The Gasoline Piston is Used in the manufacture of Window Frames, Door Keepers, and more. Checked the compression (to rule out mechanical failure in the cylinder, rings, connecting rod, etc.). compressor shows after a couple of jerks 10 bar. it’s enough, the cylinder-piston-rings are fine.
The gasoline is fed through the carburetor. the spark plug is wet, and the top of the piston is wet.
The spark plug is clean, the gap is 0.6 mm. When cranking, there is a spark. unscrewed spark plug (its threaded skirt) temporarily connect to the cylinder with wire and crank the starter. everything is okay.
There is compression, there is gasoline, there is a spark, but does not start. then there is a problem with the ignition (ignition advance angle). But the ignition timing on the trimmer / gasoline saws, on such two-strokes are not adjustable! Therefore disassemble the trimmer for grass. take away the engine from the shaft with the starter. Open magneto. a coil with two leads, contacts and two “cheeks” core, which at some point are closed by a magnet embedded in the flywheel, which clings to the starter when cranking. It was found that this closure (it can be seen. it is the alignment of both ends of the magneto core with such well-delineated magnet areas in the flywheel, the gap there is a fraction of a millimeter, while in other flywheel positions over the magneto remains a few millimeters) far from coincides with vmt (top dead center) of the piston (this point is easy to find, turning the shaft, observing the piston in the hole where the plug is twisted out).
Here’s the breakdown! The magneto should close somewhere near “vmt”, and it closes when the piston has gone somewhere down! Unscrew the nut holding the flywheel to the cone shaft. Is found: a pin that fits into the grooves on the outside cone of the shaft and on the inside cone of the flywheel and that mates them rigidly in one position has been cut. Flywheel “turned”. Most likely, someone with too much dope ripped the starter, and ripped the flywheel, knocking out the ignition (trimmer for grass American, should be easy to start and a child, the force is not needed, but there are tractor drivers with experience starter diesel, for them, this technique is soft).
If there is no standard pin, you have to make it yourself: a small plate, bent “U”, so that it goes into two slots in the flywheel with its “horns” and in the wide slot on the conical shaft with its bent part. Experimentally sized so that the flywheel lowers on the shaft and locks securely in place.
Check the alignment of the magneto and “vmt” closure, tighten the flywheel nut, assemble the grass trimmer, start according to the instructions.
Thank you very much Yuri for such useful information!
Preparatory moments
Before replacing the piston or rings (the cylinder as a whole), you need to get to the cylinder. For beginners who have no idea where this element is located, here’s a hint. The muffler is just bolted to the cylinder. In case you have no idea how to properly put the piston on a scooter 4t or 2t, you must first remove the old CKG. The upcoming repair can be divided into the following steps:
- Removing the scooter trim (plastic);
- Disconnecting the electrical wires;
- Disconnecting the oil hose;
- Disassembling the engine;
- Removing the old piston, rings (CKD in the aggregate);
- Installation of new parts;
- Mounting the engine, connecting the wires and hose;
- Fastening the plastic.
Plastic folded aside so as not to crush if careless. All the bolts and screws are put in a pile, sorted individually if necessary. After making sure that all the hoses with gasoline and oil are disconnected, remove the engine. It should be understood that the removal of the engine differs depending on the design features of the scooter model. Once the engine is removed, you can begin to remove the plastic cover that protects the cylinder head from external factors. Then the cylinder head can be removed. It is fastened with 4 bolts. So as not to damage the threads, all the bolts are unscrewed crosswise.
Remove the cylinder and inspect it immediately. If there is no damage, it can still be used. While the piston is probably not reversible.
Engine
Lifan company installs several types of engines of different capacities and modifications on its scooters. The most popular is the diesel single axle tractor 186FD. However, this configuration from the manufacturer costs an order of magnitude more, which means that most consumers still choose the familiar models with a gasoline four-stroke engine.
In order to avoid malfunctioning engine Lifan, you need to carefully monitor its condition and carry out timely maintenance. Consider the main parts of the power unit and possible malfunctions of the engine Lifan, as well as ways to fix them.
How to Fit Pistons and Connecting Rods
If you are building a V-shaped engine, keep in mind: if the lower connecting rod head has a wider chamfer on one side, it must face the notch (rounding) of the crank pin of the crankshaft.
If the connecting rods are designed for use with a crankshaft, without clearly defined chamfers. Then the orientation of the connecting rod can be determined by the position of the “locks” bearing shells: facing outside the block or inside (towards the camshaft. if it is in the camber of the cylinder block).
For example, the “locks” of SBC and BBC liners must face outward. Other bearing shells have the “locks” pointing inward. the position of the bearing shells has no effect on the performance of the bearings themselves. You just have to get the orientation right.
If there are no chamfers on either side of the rod bottom head, then the half bearing shell must be offset from the crank pin flange, so its edge doesn’t get caught in the rounding.
Through-holes in the top and bottom heads of the connecting rod
Often the connecting rod has a through hole in the bottom head for lubrication of the cylinder wall. These holes are not designed to lubricate the camshaft, as some people think.
Sometimes the hole is only on one side of the rod lower head. For these types of connecting rods, face the bore in the bottom head toward the camshaft, toward the camber of the cylinder block.
Tractor T-25. Installing Piston Rings (1080p)
the hole in the top head of the connecting rod (be it at the top or at an angle to the side) serves to lubricate the piston pin. So its orientation in the engine doesn’t matter.
Connecting rod bearing “locks”
“The main feature of this new feature is to put the tractor in the right place in the right way on the head of the crank pin and the lid of the crank pin. They do not prevent the bearing shells from turning, since the bearing shells are held in their “bed” by the tension created by properly tightening the cap bolts.
“Proper” liners, when mounted properly, protrude slightly beyond the lower head connector fishing line. Therefore, after tightening the bolts, they are firmly fixed in the “bed”.
Recently, many engines have been using camless liners (examples are the Chrysler 3.7L and 4.7L). By eliminating the machining of the grooves in the connecting rod and bearing cap and the “locks” on the bearing shells, machining costs are reduced. When installing these bearings, they must be placed in the exact center of the connecting rod lower head.
Figure. 1 If two connecting rods are mounted on the same crankshaft crank pin in a V-engine, the notch side of the connecting rod lower head should face the adjacent connecting rod.
Fig. 2 in this case the larger chamfer on the lower connecting rod head faces the crank pin lug.
Fig. 3 The bearing retainer tab and notch in the bottom head is only needed to position the bearing shells correctly in the connecting rod. “Locks” will never keep the shells from turning in the connecting rod if there are any irregularities during assembly. example: the bolts in the rod rod rod’s bottom head are not properly tightened, or the rod hole in the bottom head has lost its shape.
Figure. 4 The bearing shells are only held in place in the connecting rod by a radial load from the preload on the shells when the lower head cap retaining bolts are tightened to the proper torque. To get the proper amount of clearance the liner is made slightly longer than its seat. So when you install the bearing shell by hand in the “bed” it will be a little bit higher than the parting surface. This is how it should be. under no circumstances should the edges of the shells be filed or trimmed!
Crush Height Each Half Bearing. Bearing shells protruding over the split surface. shell Cap. crush height Each half bearing cap Radial Pressure. radial force
Rice. 5 Measure the maximum piston diameter at a well-defined location, since the piston skirt has a “barrel-like” profile, and piston height readings will vary significantly.
Figure. 6 A through hole on the side of the connecting rod (top) head (top photo) can indicate press-fit fit of the pin in the connecting rod. Second photo shows the same crank pin from the outside. And here’s the hole on top of the crank pin (third photo) for better lubrication of the floating piston pin.
Figure. 7 The bottom of the piston usually has a notch (such as an arrow with “FRONT” written on it). piston and connecting rod offset (as pictured) help orient the piston for proper engine assembly.
Figure. 8 If the pistons are designed for V-engines, they are usually marked with an “L” on the underside. if installed on the left side of a cylinder, or “R. for the right hand cylinder row.
connecting rod offset
There are some engines that have a connecting rod rod offset from the top or bottom heads (when viewed from the side “in profile”). Connecting rods of this type are used in V-engines with left and right side cylinder rows that are “offset,” forward and backward in relation to one another. Depending on the specific engine model, this piston rod can have an offset of 2.5 mm or more.
If in doubt, make sure the connecting rod upper head is centered on the piston in the pin bosses.
Do counterclockwise rotating engines need to have pistons in the “opposite” direction??
On a reverse-rotating engine. when the crankshaft rotates counterclockwise when viewed from the front of the engine. the connecting rods are usually mounted in the same manner as in a conventional engine whose crankshaft rotates in a clockwise direction. That is, the larger chamfer on the bottom head of the connecting rod will still face the notch on the crank pin.
However, if pistons with an offset piston pin are used, then the piston must be mounted “backwards” (rotated 180 degrees) from its “standard” position. The piston pin in this type of piston is offset on the loaded side of the piston skirt.
In a clockwise rotating engine, the loaded side of the cylinder faces the intake manifold on the left cylinder row (“driver” side) and the exhaust manifold on the right cylinder row (“passenger” side).
In a reverse-turn engine, the pressure on the cylinder wall from the piston is directed in a different direction: on the exhaust side to the left and on the intake side to the right. If the pistons are symmetrical (t. е. left and right side of the piston are loaded differently when the engine is running and do not have an offset piston pin), their orientation only depends on the valve headings on the bottom. these must be aligned with the valve positions.
Piston skirt design
The shape, area, and mass of the piston skirt play an important role in friction loss and piston stabilization when rearranged at the top and bottom dead points. Here we show the role of loaded and unloaded sides of the piston and the development of asymmetric skirts designed primarily for weight reduction.
the left and right hand sides of the piston are loaded differently when the engine is running. This is why the design of the piston skirt plays an important role in the distribution of perceived loads. in terms of strength and piston weight.
The piston skirt must be able to support the pressure on the cylinder wall while reducing friction. And its area must be such that it is strong while providing stability to the piston to minimize “wobble” relative to the pin axis as the piston moves up and down. And the loaded side of the skirt has the greatest load on the expansion stroke.
If the crankshaft rotates clockwise (when viewed from the front of the engine), the loaded surface of the piston crown faces the intake manifold on the left cylinder row (driver’s side) and the exhaust manifold on the right cylinder row (passenger’s side).
The less loaded side of the skirt bears the load on the compression stroke. This difference in load is due to the position, the angle between the connecting rod and the piston, as it moves.
There is a tenfold difference in the load on the different sides of the piston skirt over the cycle time! The load on the piston skirt may vary with piston stroke, connecting rod length, and maximum cylinder pressure.
For this reason, asymmetric pistons must be special. for left and right cylinder rows. Arrows or other markings are then applied to the bottom of the piston to indicate the front of the engine.
Fig. 9 This photo shows asymmetric pistons for the left and right cylinder rows of a V-engine. Their feature is a wider portion of the piston skirt on the loaded side and a tapered portion on the lighter side.
Figure. 10 Another example of an asymmetric piston. Note how the piston pin bosses are flattened, allowing the piston pin to be made shorter and lighter. Also, although almost invisible to the eye, the pin axis is displaced 0.50 mm toward the loaded side of the piston (toward the wider portion of the skirt) in order to reduce the imbalance due to the weight difference between the “narrow” and “wide” portions of the skirt.
Weighted side of piston skirt
When the piston moves down in the expansion stroke, it experiences considerable resistance in an attempt to turn the crankshaft. As the load increases, so does the drag. In doing so, the loaded side of the piston skirt takes lateral pressure that increases the load (with increasing friction and wear) on the corresponding side of the cylinder wall.
If there is a notch on the bottom of the piston (such as a dot or arrow or “Front” lettering), it is important to install the piston according to this notch, usually indicating the front of the engine.
The unloaded side of the piston skirt
This part of the piston skirt is opposite to the loaded side. This operates when the piston moves upward during the compression stroke due to resistance created by the compressed fuel-air mixture. Its main purpose is to ensure the stability of the piston as it moves through the cylinder. That’s why this part of the skirt can be narrower, to save weight.
So, in order to fine-tune the distribution of these forces between the different sides of the skirt, asymmetric pistons have been developed that have a wider skirt on the loaded side and a tapered skirt on the opposite side. This ensures optimal distribution of loads on the piston skirt while reducing the weight of the piston.
One example is the “asymmetric” (or T-shaped) design of JE Pistons FSR pistons that feature a wider skirt on the high-load side and no skirt at all on the boss side, allowing for a shorter and lighter piston pin. Pistons of this design were originally developed for racing engines.
Another advantage of such pistons is the improved working conditions for the piston rings. But basically the skirt design, combined with a slightly offset piston pin, significantly reduces friction loss.
Fig. 11 This diagram shows how to determine the loaded and unloaded sides of the piston skirt.
Thrust Load. lateral force effect Minor Thrust Side. unloaded side of the cylinder Major Thrust Side. Loaded side of cylinder Red curved arrow. crankshaft rotation direction
Figure. 12 This photo clearly shows the difference in piston skirt width between the loaded (left) and unloaded (right) side of the piston.
Figure. 13 Computer simulation shows how mechanical loads in the piston are distributed when the engine is running at partial loads. (The darker the colors, the less the load and the brighter the more).
Fig. 14 And this diagram shows how the piston is loaded immediately after the ignition of the mixture.
Fig. 15 Here the piston is shown from below. The diagram clearly shows that during the stroke cycle, the top portions of the piston pin holes (colored red) and the portions of the piston skirt immediately adjacent to them are subjected to the highest mechanical load.
Fig. 16 A thin layer of anti-friction coating (dark color) on the piston skirt helps retain oil and reduces friction between the piston and cylinder. especially when the engine is cold.
Piston pin misalignment
Asymmetric pistons may also have piston pin offset. In doing so, the pin axis is offset from the piston axis to the loaded side by about 0.51 mm. This slight offset “balances” the piston by compensating for the difference in skirt weight, as well as reducing the force applied to the loaded side of the piston.
Again, referring to the experience of JE Pistons, the asymmetrical piston makes the piston pins shorter, stiffer and lighter (by about 10 grams).
We hope this article helps you become more familiar with the intricacies of engine assembly. Remember, it is best to mark the pistons and connecting rods before disassembling. Competent answers to your questions and help with technical problems with engines. our main task.
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Installing the piston in the cylinder block
you have to manually push the ring, gradually pushing the piston into the cylinder.
Correct installation of piston rings
Sooner or later your engine will wear out and will require either a change of piston rings, or the piston as a whole.
Like changing piston rings. it is an ordinary task, accessible to everyone who is little or no more familiar with the device and the principle of the primitive four-stroke motor. But, unfortunately, people are afraid to spend 15 minutes of their incredibly precious time to read the literature and shove everything into the engine on the principle (and that’s how it was standing). probably will work). Well, flag in your hands and get to the service as soon as possible.
Well, for those who care about how their engine performs after a rebuild, you should read this article.
So, we take a piston and see 3 blanks for installation of piston rings. There are no restrictor stoppers on 4-stroke engines like there are on 2-stroke engines, for example.
There are two types of piston rings on 4-stroke engines. The first two, which are installed in the top two holes, are compression. Even from the name it is clear that they are responsible for the presence of compression in your engine and must hold the gases formed at the moment of ignition due to combustion of fuel in the combustion chamber.
The next three rings are linchpins. Their purpose is also immediately clear. They are responsible for removing the oil that coats the walls of the cylinder the moment the piston comes back down. If these rings leak, the oil will stay on the cylinder walls, and that can cause the engine to gobble up oil, and, of course, smoke.
How to install the primary? Yes, basically the same as they were at the factory, in the same order, but to avoid mistakes we show again.
You install the main casing ring first: the one with the corrugated structure. This one is really easy to install as it is the most elastic of all.
Next we put the upper and lower SOFT liners. They are a little bit harder, but there are no problems with their installation either.
Now put the piston compression rings: the ones that are thicker and “harder”. First we install the lower one, then the upper one. They are a little bit harder to fit as they are less elastic and harder. You can hardly break them, but if you have absolutely wrong hands, they will be extremely easy to bend.
The point is that the rings still need to be properly positioned on the piston, so that the ring locks (the kerf spot) do not get on top of each other. Simply put, it is necessary that the kerf of the lower ring is not directly above the kerf of the upper ring.
put the lock of the bottom ring in the middle above the cavity of a valve, for example, inlet valve (it can be an outlet valve, there is no difference).
The lug of the top ring is positioned strictly opposite to the bottom ring. Accordingly, if the lower ring lock is over the inlet valve cavity, the upper ring lock is over the outlet valve cavity.
Now move on to the wear rings. These rings should be positioned in exactly the same way, so that no one locks. Therefore, place the upper ring over the piston pin hole, on the right side.
The second ring (the lower one) is placed on the opposite side, also about in the middle of the piston pin hole.
put the last wavy oil ring in any of the four sections between the pin hole and the valve cavity.
And now to your question: what kind of nonsense the author is rubbing us here? And why so painstakingly align all 5 rings?
Explanation. We did all this so that when one lock was placed over the other, no gases would pass through these locks (in the case of piston rings) and no oil would remain on the walls (in the case of linchpins).
If to take into account piston rings, it is the loss of compression and the passage of red-hot working gases to the intake rings, which are not designed for such suddenly occurring high operating temperatures. As a result, the rings can burn out after a certain period of time.
If we refer to the intake rings and the alignment of the locks on them, then we will not have oil completely removed: it will reach the piston rings, which will lead to coking of the rings grooves, and as a result they will get stuck and then burn.
As a result, you get burnt rings and piston wear.
Bottom line: setting the rings’ locks before installation is a matter of 2 minutes, and this operation can prolong the service life of the motor by dozens of hours.
The general algorithm for setting the gaps
To begin with, you should carefully study the instruction manual for your power tiller. There are two torques to be found in it:
First. Recommended by the engine manufacturer, the correct value of clearances. They are different for different models of internal combustion engines. They can be the same or different for the intake and exhaust valves.
For example, the norm may be 0.1-0.15 mm for both valves. Or 0.15 for intake and 0.20 for exhaust. A larger gap may be recommended on the exhaust ones, as they are heated more by the exhaust and are more subject to thermal expansion.
The second. Next, you need to find information in the Instructions on how to set the third compression stroke, in the position of which the gaps are adjusted. For this purpose, on the flywheel and cylinder of most engines there are risks. The flywheel is rotated until they are in line.
If there are no marks, the instructions do not say anything, the third compression stroke to adjust is found as follows:
- Remove valve cap.
- Unscrew spark plug (on gasoline engines).
- Rotate the flywheel slowly. Keep an eye on the valves. The following should happen:
- Exhaust valve open and closed.
- Intake valve is open and closed.
- After the intake is fully closed, slowly turn the flywheel another quarter or half turn. The piston should be on the way to TDC or just at TDC, be on the compression stroke, but not yet going down.
- Check the position of the piston with a feeler gauge through the spark plug hole.
Adjustment is carried out when the engine is cold. Then there is a general procedure for all engines:
- The adjusting screw locknut (in the photo in the foreground) is loosened.
- A feeler gauge is inserted under the rocker arm, in this case 0.15 mm (see “8”). photo).
- Tighten the adjusting screw until the rocker arm is flush with the dipstick. The dipstick is moved slightly, the screw is tightened until the dipstick begins to move with little force.
- Tighten the loosened locknut.
The dipstick should also be pulled out with a little force.
How to properly adjust the valves with a motor block with Chinese engines Lifan 168F-2,170F,177F shown on the
After tightening is complete, the gaps should be checked again with the feeler gauge. It may happen that the screw is turned when tightening, or a lock nut and screw is turned and the settings are lost.
Exactly the same procedure is repeated with the other valve.
If the manufacturer recommends different gaps for intake and exhaust valves, they should be distinguished:
This is not a complicated operation, but it requires close attention because the clearances are adjusted to a negligible value, with an allowable error of “hundredths” mm (0.05 mm). On some models, even less (.0.02 mm).
Installing Piston Rings on a Single Axle Tractor
Piston rings form the seal between the cylinder wall and the piston. Should provide a good seal over the entire cylinder plane in a wide temperature range. Three rings are more commonly used in four-stroke engines; two are compression rings and a bottom liner.
- Compression rings provide a positive seal between the cylinder and piston to seal the combustion chamber.
- Heat transfer from the piston to the cylinder walls.
- Wiper rings remove excess oil from the cylinder walls, preventing it from entering the combustion chamber. However, they do not completely remove it; they regulate it by leaving the amount of oil necessary for the compression rings.
First compression ring
solely for the purpose of preventing expanding gases from entering the combustion chamber. During the stroke cycle the increasing pressure in the combustion chamber presses the first compression ring against the bottom of the piston groove and presses it harder against the cylinder walls, thereby ensuring an adequate insulation of the combustion chamber. the pressure in the groove of the ring is retained on subsequent strokes without having time to decrease. The clearance between the ring and the groove is 0.04-0.08 mm
Protects the second ring from high combustion temperatures and reduces the load. Has the greatest heat transfer from piston to cylinder, with compression rings accounting for approximately 50-60% of the heat transfer from piston to cylinder. Some of the gases escape, the second ring begins to fulfil its function, more on this later.
The first compression ring is made of high ductile iron or steel that can withstand high temperatures and stress without having a high coefficient of thermal expansion. During engine operation the temperature of the ring reaches 180-210C, in the upper dead point where there is practically no lubrication due to friction, an even higher temperature is reached. Often has a special coating on the outside of the ring face to reduce friction. It can be plasma cladding of molybdenum, ceramic metal, ceramics. commonly applied by electroplating, the chrome coating is matte gray and has a peculiar porous structure to retain oil for greater friction reduction. The other surfaces are black as a result of phosphating. The coating provides anti-friction and anti-corrosion properties.
Compression rings are not made completely round, but have a complex arc shape in the free state and a sufficiently large end gap. When the ring fills the piston and is inserted into the cylinder, it provides even contact pressure all around the cylinder.
Second compression ring
Works in more favorable conditions and performs the function of an additional seal Also, due to its special shape, it helps the wiper to remove excess oil, leaving only an oil film on the surface of the cylinder. Average ring temperature of 150 to 170 C in operation. The clearance between the ring and the piston groove is slightly less than for the first one.03-0.06 mm. Made of cast iron and very brittle. The variety of ring shapes results in certain functions. such as load distribution in the groove, reduction of piston skirt friction by aquaplaning on oil, removal of excess oil.
The bevel on the inside of the ring determines in which direction the ring will bend. If the bevel is on the bottom, the ring will turn out with the outside surface downwards after heating as shown in the picture. And so if the bevel is at the top, the ring face up is everted.
Wiper ring
Underneath the compression rings, there is an oil release ring that acts to remove excess oil from the cylinder walls.
Large amounts of oil penetrating through the compression rings into the combustion chamber is bad for engine operation. In the process of work, combustion oil is deposited on the walls of the valves, the combustion chamber, the plugs, the bottom of the piston. Heavy soot build-up heats up, increasing the chance of detonation. Exhaust valves are subjected to increased thermal stress.
The thin film of oil left on the intake rings reduces the frictional force of the compression rings, increasing their lifespan. unlike compression rings, lube oil rings are not pressed by the working pressure of gas to the groove plane in the piston and the cylinder walls, so they have special axial and radial expander rings.
Two types of rings can be distinguished by their design: boxed and collapsible, and both types can have different reamers.
As the piston moves down, the wear rings scrape excess oil from the cylinder walls, guiding it through drainage holes in the piston back into the crankcase. An oil wedge in front of the ring helps lubricate the piston skirt effectively. The walls of the cylinder are roughened, the so-called honing, which allows a thin layer of oil to be retained for the compression rings.
Set rings, consisting of two thin steel plates, (often having different coatings to reduce chafing) and a tangential expander that performs both axial and radial expansion are more common. Used in modern engines.
Features of installing oil rings
I want to draw your attention to installing the oil rings. There should be no problem with compression rings if you follow the simple rules, place them with the lettering up (lettering, dot) and use a special tool.
When you install the oil sealant can be difficult in the absence of the inscriptions, or the correct installation of the expander lock. Let’s look into this in more detail. If the inscriptions are missing, it does not matter which side you put the ring and which one is up and which one is down (dialed).
Often mistakes occur when installing the piston in the cylinder, even when using a special collar to tighten the rings on the piston. The special feature is as follows. When assembling an oil ring, pay attention to the expander’s lock and the correctness of its joining. See image below for clarity.
During compression of rings on a piston the lock of expander of an oil ring can jump off from correct position and lie in overlapping gathering on a spiral, thus plates fall through the expander and it will lead to scoring of walls of a cylinder, and grooves of a piston. To avoid this, the binding collar should be positioned as shown in the image.