How to properly install rings on a two-stroke scooter piston

Installing a piston with a larger volume than stock is perhaps the simplest, most affordable, affordable and effective way to significantly increase the maximum speed and power of a scooter. There are, of course, even more effective ways to increase maximum speed and power, but these methods, or rather the hardware, cost simply unrealistic money...

If you charge the engine of the same 139QMB to the maximum, then such tuning before the “increase” cost the client about 35,000 rubles and this does not include work.

It is clear that not everyone can afford such amounts. Yes, even if it’s affordable, what’s the point? It’s easier to buy an old branded scooter and ride it than to charge the “Chinese” and then throw it in the trash after a season. But that's what I think.

How to install rings on a piston 4t scooter

How to install piston rings on a scooter
Deterioration in traction, a drop in maximum speed, blue smoke from the muffler and weak dynamics of the scooter are a sure sign of worn piston rings or a worn cylinder-piston group. Most often it is the piston rings

, because The diameter of the piston group in scooters is small, the working area of the rings is very small and therefore they do not run for so long.

So, if you are faced with the need to replace piston rings on a scooter, and in addition to the main problem that they need to be changed, there is another one - how to correctly put the rings on the piston. You can't just take any ring and put it in any of the "grooves" on the piston. You need to understand which ring is the upper compression ring, which is the lower compression ring, and also how to correctly install the oil scraper ring.

Installing piston rings on a 4-stroke Chinese scooter. The photo below shows which piston ring is which.

As you may have noticed, the piston ring set consists of two compression rings (upper and lower), as well as an oil scraper ring, which consists of two regular (thin) rings and a central expander.

The second compression ring is dark black

color, as well as unique (beveled) geometry.

The color of the rings may vary among different manufacturers, for example, for the CMR company - the lower compression ring is red

color.

The following diagram shows the correct placement of the rings.

You can see inscriptions on the compression rings, they may be different depending on the brand of the rings, but their essence is the same - installation of the rings should be done with the inscriptions UP

! Those. the inscriptions must be directed towards the cylinder head.

As a rule, there is no inscription on the oil scraper rings (two thin ones), so they can be placed on either side, the main thing is that a so-called expander is installed between them, as shown in the photo below.

We will omit the process of installing rings on the piston, because there's nothing complicated there

You should only be careful when inserting the rings into the grooves, because the rings are made of high-strength cast iron and strong tensile stress may cause the rings to break

If you did everything correctly, then in the end the rings on the piston should be installed, as shown in the following photo.

Next, before installing the piston into the cylinder, it is necessary to move the ring locks to the correct distance.

At this point, all the features of installing piston rings on a four-stroke scooter have been announced; now you can install the piston in the cylinder, having previously lubricated the rings and cylinder with oil.

Installing piston rings on a 2-stroke scooter. So, let's say you purchased a new piston with rings and want to install it on your scooter. The piston kit for a two-stroke scooter comes with only two compression rings.

In some cases, depending on the scooter model, the rings may also include a so-called expander or, as it is also called, an expander. Such an expander is installed under the second (lower) ring.

Before you begin installing the rings on the piston, you need to understand where the upper compression ring is and where the lower one is. Because the rings are very different in geometry, incorrect installation of one of the rings will lead to its breakage

Please note that the top ring has an internal bevel, please inspect each ring carefully before installation. Below is an installation diagram that clearly shows where which ring should be placed, as well as where the expander is installed, if one is included in the kit

It is important to note that the rings have an inscription on the surface, which should be at the TOP! Those. the inscriptions must be directed towards the cylinder head

The main thing is to be careful, because... the rings are very fragile. Try to carefully insert the rings into the grooves, without exerting too much tension.

In conclusion, I would like to note that two-stroke pistons have pins that prevent the rings from turning.

Therefore, when installing the rings into the grooves, pay attention to the locks of the rings - they should converge on the pins, as shown in the photo below

Now that the rings are in place, you can begin installing the piston into the cylinder, having previously lubricated the rings and cylinder with oil.

Preparatory moments

Before replacing the piston or rings (CPG in total), you need to get to the cylinder. For beginners who have no idea where this element is located, we will tell you. The muffler is just bolted to the cylinder. If you have no idea how to correctly install the piston on a 4t or 2t scooter, then first you need to remove the old CPG. The upcoming repairs can be divided into the following stages:

Removing the scooter trim (plastic);
Disconnecting electrical wires;
Disconnect the oil hose;
Engine dismantling;
Removing the old piston, rings (CPG in total);
Installation of new parts;
Engine installation, wire connections and hose;
Plastic fastener.

The plastic is folded to the side so as not to be crushed if careless. All bolts and screws are placed in a pile and, if necessary, sorted separately. After making sure that all hoses with gasoline and oil are disconnected, remove the engine. It is necessary to understand that engine removal differs depending on the design features of the scooter model. Once the engine is removed, you can begin to remove the plastic casing, which protects the CPG from external factors. Then remove the cylinder head. It is secured with 4 bolts. In order not to break the thread, all bolts are unscrewed crosswise.

Preparation for the procedure

You need to start by cleaning the exterior of the scooter from dirt, sand, and dust. The work itself must be carried out indoors, where there is no risk of debris getting inside the mechanisms from the outside. Operations may be carried out outdoors, but subject to the following conditions:

the air temperature should be 18-25 degrees;
little or no wind;
the presence of a flat, hard surface for repairs - concrete or asphalt are best suited;
It is not recommended to open the inside of the scooter for at least two hours after turning off the engine for safety reasons.

For fastening, you will need to prepare a box with cells for each type, so as not to lose or mix up the varieties. The work may take about an hour depending on your skill level. If you lack experience, it is better to call another person for help and carefully record what was removed (and in what sequence) in order to reassemble the vehicle correctly after everything.

How to properly install rings on a two-stroke scooter piston

There is nothing complicated about installing rings on the piston of a two-stroke scooter, as well as a four-stroke scooter, and many people know this. But most scooter riders who have only recently acquired such equipment have no idea how to replace the piston on a scooter, how to correctly install the rings on the piston, where the arrow on the piston should point, and much more.

In this lesson, I will tell you how to properly put the rings on the piston and assemble the piston in place. Since we have already talked about four-stroke engines before, here we will talk only about two-stroke engines. So, our piston is worn out and requires replacement.

The rings and piston wear out first, and usually only those need to be replaced. If the piston is severely worn, it is necessary to bore the cylinder. It is also bored when the piston jams in the cylinder, forming deep scratches on the walls of the latter. There's nothing wrong with that, and if your new cylinder has been properly bored (for which you'll only need to shell out about $10), it will need a ring repair kit with a new piston. Such rings are marked 0.25. The second boring is 0.5, respectively, etc. to one.

After purchasing 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 corrugated ring (more on its purpose later), a piston pin and two piston pin retaining rings.

Now about the third ring in the set. Its purpose is to spring the lower compression ring. It installs it directly under it, and usually does not provide any benefit during operation. You can throw this ring away or you can put it in, it makes no difference. Many piston manufacturers do not include it at all.

It's time to put everything back in place. Depending on the scooter model, compression rings may be the same or vary in thickness and cross-section. Most pistons for Honda scooters, for example, have different rings, where the upper one is thinner than the lower one and has a different cross-section.

You should definitely pay attention to this when installing; the top one is thinner and ground 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 to the finger

First you need to put on the bottom, then the top. There is no need to stretch or bend them. These manipulations must be carried out carefully

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 to the finger. First you need to put on the bottom, then the top

There is no need to stretch or bend them. These manipulations must be carried out carefully.

There are locks in the grooves for the rings that prevent the rings from turning during operation, so the ring gap must be 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 inscription EX. Both the arrow and the inscription must be directed towards the exhaust (2). In this case, the ring locks will be located on the side of the reed valve. If the locks are placed towards the exhaust, the piston will not last long, the rings will be pulled into the exhaust port and gradually grind it down.

During all manipulations with the piston, it is imperative to put a rag in the crankcase window so that nothing inadvertently gets in there; we still need a crankshaft with bearings.

When installing the piston pin, pay attention to the condition of the separator (bearing); it may need to be replaced. Before installing the piston pin, install the snap ring on one side before installing the piston (usually on the side where you will not be able to fit the pin and the second snap ring in)

Then place the pin with the bearing and the second retaining ring; when fixed in the groove, it will make a certain click.

That's all, now put on the cylinder, not the piston (remembering to check the condition of the gaskets and lubricate the piston and cylinder walls with engine oil), the cylinder head and tighten the bolts one by one in a cross pattern.

You can also read other articles on the topic:

How to determine piston wear

Now let's check the gaps at the joints of the rings by placing them in the cylinder. The rings need to be removed from the piston and inserted inside the cylinder. To obtain correct readings, the ring must be in the working plane. You can set them exactly by pushing them deep with a piston.

Scooter piston ring clearance

The nominal gap at the junction of the compression rings should be within the range of 0.1-0.25 mm. With an opening of 0.4 mm, the rings must be replaced
The nominal gap at the junction of the oil scraper rings must be within 0.1-0.4 mm
The nominal end clearance (compression ring - piston groove) should be within the range of 0.03-0.05 mm, and the largest - 0.1 mm
The numbers in the interface between the piston pin and the connecting rod head. The difference in the measurements obtained should be 0.005-0.01mm (without needle bearing)

If the gaps are larger, the piston is rejected, including if you are satisfied with the other points of suitability. A more significant gap indicates that the service life is completely exhausted and the need for complete engine repair. If, according to all the characteristics, the scooter piston is suitable for subsequent use, you need to diagnose the unit. Experience shows that very often, with fully working pistons, the block can have a lot of wear, and on the contrary, the “death” of the piston does not mean the “death” of the block.

Installing the timing chain tensioner

If you have a 157QMJ series engine, do the following: unscrew the plug on the tensioner body; We insert a thin flat screwdriver into it and begin to tighten the bolt until the tensioner rod goes inside the body.

Without releasing the screwdriver while simultaneously holding the tensioner body, with your free fingers, insert the tensioner into the cylinder, screw it in with bolts, and only then release the screwdriver and screw the plug into place.

If you have a 139QMB series engine, then do this: unscrew the plug from the tensioner housing and remove the spring; push the rod inside the body; install the tensioner in the cylinder; insert the spring into the housing and screw in the plug.

After installing the piston, do not forget to adjust the thermal clearances of the valves and break in the engine.

It is worth noting that durable and trouble-free operation of the piston largely depends on the correct installation of the rings. There is absolutely no need for haste and dirt in this matter. Do everything carefully (for yourself, after all), slowly and most importantly: keep it clean!

First, let's take a little look at what a standard set of piston rings for a four-stroke scooter engine is. The standard kit consists of: two compression rings (upper and lower) and one oil scraper ring, which in our case has a collapsible design.

A set of piston rings for a two-stroke scooter engine differs from the previous one in the absence of an oil scraper ring; also, a set of rings for a two-stroke engine may include an expander (marked with an arrow).

So, we have more or less figured out the kits - it’s time to get down to business. We prepare in advance small strips of tin or thin plastic, with their help we will put the rings on the piston.

We thoroughly wash the rings and piston; when installing new rings on a used piston, do not forget to clean its grooves from carbon deposits, otherwise the new rings will not fit into the cylinder. We prepare a clean workplace and perform the installation.

We take the oil scraper ring expander from the kit and place it in the lowest groove of the piston.

In the same way, we install the expander from the kit for a two-stroke engine (if any), with the only difference being that the expander lock should be located in the area of the locking pin (marked with an arrow) of the piston groove.

We look for marks on the rings, apply pre-prepared strips to the piston, very carefully and slowly pull the rings along our strips onto the piston, in this order: first we put on the oil scraper ring, then we put on the second oil scraper ring, then we put on the lower compression ring (dark) and only then put on the upper compression ring (light). The marks on the rings after installation should be located upward towards the cylinder head.

We straighten the rings so that they stand exactly opposite their grooves and slowly pull out our strips from under them. Now the main thing: after you have pulled out the strips and the rings are in their grooves without fail, check each ring for mobility. The rings in the piston grooves should rotate freely in different directions.

The oil scraper ring should look something like this after installation:

After installation, the marks must be directed strictly towards the cylinder head.

Immediately before installing the piston into the cylinder, the piston ring locks must be moved apart in the correct order. This is done like this:

We unfold the upper compression ring so that its lock moves relative to the piston pin axis by approximately 45 degrees, and unfold the lower compression ring so that its lock moves approximately 180 degrees relative to the lock of the upper compression ring.

We rotate the upper oil scraper ring lock 90 degrees relative to the lower compression ring lock, and rotate the lower oil scraper ring lock 180 degrees relative to the upper oil scraper ring.

The photo shows approximately how the piston ring locks of a four-stroke engine should be positioned:

Red marks indicate compression ring locks. Blue marks indicate oil scraper ring locks.

Before final installation of the piston, the piston ring locks of a two-stroke engine must be positioned strictly in the center of the locking pins.

Cylinder installation

This is the final stage and must be approached with caution. After all, if the fastening is incorrect, the slightest gap will not provide the necessary compression. As a result, the scooter will not start. Install a gasket between the engine and the cylinder, and between the cylinder and its head. The head is clamped with bolted connections crosswise. It is easy to check the correctness of the work performed. To do this, you need to start the engine. If the motor runs smoothly, everything is done correctly. You can also make a few efforts with the kick starter to feel the compression.

As you have already killed yourself, there is nothing complicated. Installing rings on a scooter piston and replacing the CPG in total do not require any special knowledge. All you need are details, time and desire.

Installing a piston engine (CPG) on a 4t scooter

We take a new piston kit for 72 or 80 cubic meters (piston diameter 47mm or 50mm, respectively). You can, of course, use a standard new 50 cc CPG. The kit includes: cylinder, piston, piston rings, pin, retaining rings, as well as head and cylinder gaskets. You can buy a 72 cc cpg at a low price in our online store.

Installation is carried out in the reverse order, having previously lubricated the cylinder, piston and rings with a small amount of oil. We first install a thin ring on the piston in the lower groove, then an oil scraper ring and again a thin ring (the wavy ring - the oil scraper ring will thus be between the two thin ones in the lower groove). Next, install 2 compression rings (which are thicker). The cuts of all rings should not be located on top of each other. After installing the rings, place the piston on the crankshaft connecting rod, fix its position with a finger and locking rings. We take the connecting sleeves from the old cylinder and insert them into the new one.

We put a gasket under the cylinder on the studs

Carefully place the cylinder on the piston with rings so as not to damage the cylinder. We push the chain into the groove for the chain

Then install the chain bar on the cylinder head. Now we can put the chain on the camshaft sprocket (the position of the sprocket should be as follows: a large hole at the top, and two small ones on the sides, parallel to the edge of the cylinder head). We fix the position of the cylinder head with the gasket by screwing it on. Then we install the plastic cylinder head cover, chain tensioner, carburetor and muffler. The installation is now complete!

If you haven’t changed the oil for a long time, you need to change it before starting with a new piston. Before putting a full load on the scooter engine, it is necessary to run-in, i.e. drive 300-500 kilometers at a speed of no more than 40-45 km per hour.

Along with an increase in the power of the scooter with the installation of a tuning cpg, the load on the variator with the gears of the gearbox also increases. Remember this and if possible, replace the variator with gears with tuned ones (more reinforced.)

Photo report: Installing a piston 170CC instead of the standard 150CC on a scooter

This article will talk about how to moderately tune the 157 QMJ engine of the Racer Taurus scooter or any other scooter equipped with this engine for little money.

The tuning itself will consist of increasing the engine displacement to 170CC by installing a piston of larger diameter, and therefore volume. To the great joy of many of you, to install a 170CC piston on a 157QMJ engine you will not have to saw or bore the crankcase, change the cylinder head for another, or carry out other work on fine-tuning, adjustment, etc.

So, let's go to the store and buy a piston with a piston diameter of 61MM (170CC), the choice of piston is now very extensive, so try to give preference to Taiwanese manufacturers, their products are affordable, and the quality is much higher than Chinese ones.

This piston is made in Taiwan and costs only 1,600 rubles. The quality of this piston is quite consistent with its price; if you really want, you can find a higher quality piston, which will cost more. So, as they say: if there is an opportunity, then why not...

For comparison: on the left is a piston with a volume of 150CC 57MM, on the right 170CC 61MM.

We will begin work on the implementation of our piston with the installation of piston rings; the basic rules for installing piston rings are described in detail in the article: Correct installation of rings on a scooter piston

We take the retaining ring from the kit and insert it into any “groove” on the piston; the retaining ring should sit very tightly in the groove, evenly adhering to the entire surface and at the same time rotate freely in it.

Using a medical syringe, apply motor oil to the surface of the piston pin mounting holes, then use a needle to rub the oil evenly over the surface. In the same way, lubricate the upper head of the connecting rod.

We insert the piston pin into the mounting hole so that it protrudes slightly into the piston.

We carefully inspect the seating surface on the crankcase, remove the remnants of old gaskets and sealant from the surface, degrease the surface with gasoline or alcohol and install guide bushings (marked with arrows), put on a new gasket.

We orient the piston with the arrow towards the exhaust valve (exhaust), put the piston on the connecting rod, insert the extended edge of the piston pin into the upper head of the connecting rod and push the piston pin all the way.

This is how your arrow should end up on the piston.

We insert the second retaining ring into place.

Using a syringe, apply oil to the rings, being careful not to drip onto the gasket.

In order not to damage or deform the piston rings when installing the cylinder, we make a clamp from a strip of tin and compress the piston rings with it.

It is convenient to fix the clamp using a bracket bent from the same strip of tin.

Before installing the cylinder, carefully inspect the seating surface and degrease it with gasoline or alcohol.

Apply engine oil to the inner surface of the cylinder with a syringe and rub it evenly over the surface with a needle.

We take a piece of wire and hook it onto the timing chain.

Be careful that the timing chain does not come off its sprocket!

We pass the wire and chain through the cylinder and put it on the studs.

We begin to slowly put the cylinder on the piston, this work should be done very carefully, without applying excessive force, while at the same time making sure that the piston enters the cylinder without distortion.

Push the piston in so that the rings fit completely into the cylinder.

Remove the clamp

We finally “drive” the cylinder into its place.

The cylinder should sit in place with the force of your hands; if the cylinder does not “want” to go into place, it means you did something wrong, perhaps dirt got under the rings, remove the cylinder and do it all over again.

After you have installed the cylinder in place, check how the piston moves in the cylinder. To do this: holding the cylinder with one hand, rotate the crankshaft several times with the other hand, the piston should move in the cylinder freely from hand effort.

We insert guide bushings into the cylinder (marked with arrows).

We install the lower guide for the timing chain in its place.

We look for the T mark on the generator rotor and align it with the protrusion on the crankcase.

Be careful not to confuse the T mark with the F mark, otherwise there will be trouble!

Again, carefully inspect the planes of the head and cylinder, if necessary, clean them and degrease them with gasoline or alcohol. We install the gasket on the cylinder, use a wire to pull the chain through the head and put the head on the studs.

Before installing the head, it is advisable to remove deformations from its plane; read about this in detail in the article: Modifying the cylinder head of a scooter

Install the guide bushings (marked with arrows) into the corresponding holes in the cylinder head.

We put the chain on the camshaft sprocket and install the camshaft in its place, making sure that the upper large hole (marked with an arrow) on the sprocket is at the top and the two notches (marked with arrows) are parallel to the plane of the cylinder head connector.

Before you finally install the camshaft in place, make sure once again that the T mark on the generator rotor is exactly opposite the protrusion on the crankcase.

We install the valve bed cover, orienting it with the EX mark (highlighted in red) to the exhaust valve (exhaust).

We screw the nuts onto the studs, not forgetting to put washers under them, and screw the bolts into place.

The nuts should be tightened crosswise in several steps, first tighten nuts 1 and 4 a little, then nuts 2 and 3, then lightly tighten the bolts. Then tighten nuts 2 and 3 with a little force, then nuts 1 and 4, after tightening the nuts, tighten the bolts a little. So, in several steps, gradually increasing the force, tighten the nuts and bolts completely.

After all nuts and bolts are fully tightened, use a syringe to apply engine oil to the bearings, camshaft lobes, rocker shaft and flail.

The final step in all this work will be the installation of the timing chain tensioner.

We unscrew the bolt on the tensioner, insert a screwdriver into the hole, tighten the bolt until it stops (right-hand thread) so that the tensioner rod goes completely inside.

Holding the screwdriver from unwinding, insert the tensioner into place, tighten the bolts and release the screwdriver; the spring located in the tensioner will be released and automatically extend the rod to the required distance.

After installing the new piston, do not forget to adjust the valve clearances; this work is described in detail in the article: Adjustment, setting valves on a scooter

Also, do not forget to break in the new piston engine; the basic rules for running in a scooter engine are described in detail in the article: Proper break-in of a scooter engine

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Why do engine parts break?

Breakdowns can be planned or emergency. Planned failure depends on the manufacturer, the materials used to manufacture the group, and the intensity of use. Usually the life of a saw is calculated in engine hours. After working out the required number of engine hours, you should submit the tool for repair for engine maintenance.

Causes of unexpected piston failures:

operation under increased loads incomparable with the power of the tool;
lack of normal maintenance, which leads to dry engine operation and increased wear;
the use of low-quality fuel, which does not provide stable engine operation;
the saw is very old, despite the low intensity of use.

Each start of the tool is a certain stress for the piston and cylinder. Therefore, the life of the device also depends on the number of starts. If you notice extraneous sounds from the engine, a decrease in power, or an increase in consumption, it’s time to take the equipment to a service center for preventative repairs.

Engine wear

The main question of this article is whether driving at low speeds leads to premature wear of the engine? And what modes are the most “wear-inducing”. The organization of expert tests is, in general, clear. The engine is the same: a VAZ eight-valve engine. A stand, equipment, gasoline and several cans of oil - each test cycle requires its replacement. The task is simple - you need to “travel” the same distance, at the same speed, but using different engine operating modes. In different gears... How to achieve this? You can drive at the same speed, maintaining engine speeds of 1500, 2500, and even 4000 rpm

The higher the speed, the lower the gear; it is important that the power produced by the engine is the same. This is easy to do at the stand - we measure the torque using a dynamometer, the speed is known - therefore, we know the power

We multiply “speed” by engine hours, which we also record – that’s the mileage. With wear it is more difficult - every time, after running the engine at a fixed time for a given time, the engine will have to be disassembled and weighed the main parts that form the friction units, these are bearing shells and piston rings. Plus, there is additional intermediate control, which we will carry out by determining the content of wear products in oil samples. If they found chromium, it means that the first piston rings are wearing out; found iron - cylinders and shaft journals; tin has appeared - it will determine the wear rate of the bearing liners (since it is part of the anti-friction layer); aluminum is a consequence of wear on the pistons and camshaft bearings. The engine worked at the specified constant modes with approximately the same power, 50 hours each. Not much for the resource, but we get wear rates, and then by simple extrapolation we estimate the approximate service life of the motor. At the same time, the engine speed during the test cycles varied from 1200 to 4000, that is, more than three times. And then the load on the motor was increased - and the cycle was run again. And then - more... The result was a voluminous table, where for each point of the regime its own wear rate was recorded, and divided by units - bearings and rings.

Installing piston rings

Remove the set of piston rings from the box. A piston ring set for a Chinese four-stroke scooter usually consists of five items. Three of which are a single assembled oil scraper ring, the other two: upper and lower compression.

A typical set of piston rings looks something like this

Or so

Carefully unpack the kit with perfectly clean hands.

In the kit you will find two of the thinnest rings and one thick corrugated ring (expander) - this will be an assembled oil scraper ring that needs to be installed on the piston first.

We place an expander in the lowest groove of the piston

We place thin oil scraper rings in the same groove - one under the expander, the second on top of the expander

We find the lower and upper compression rings in the kit and install them, respectively, in the middle and upper grooves of the piston - with marks on the side surface to the cylinder head (cylinder head). The lower compression ring differs from the upper one in color (not always) and the shape of the working edge (always). In most kits, the lower compression ring is painted black, and its working edge has a slight bevel.

Piston installation

Insert a retaining ring into any boss of the piston pin. It is most convenient to insert the ring with small round nose pliers. After installation, check how well and tightly the retaining ring fits.

If the retaining ring does not cover the entire surface, but only a small part of it, replace it with a new one.
If the retaining ring does not lie tightly in the groove and dangles, straighten it a little

Lubricate the bearings of the lower and upper connecting rod heads and the piston pin bosses with clean engine oil. We put the piston on the connecting rod, orienting it with the “IN” mark to the inlet port; if there is an “arrow” on the piston instead of the “IN” mark, orient the arrow to the exhaust port. We insert the piston pin into the boss - orient the piston on the connecting rod so that the pin hits the connecting rod - install the pin all the way into the locking ring and secure it from falling out with the second locking ring.

We install the cylinder guide bushings on the studs and put on the gasket. It is advisable to place the gasket on the sealant, but without fanaticism.

Features of choosing rings

In order for the engine to operate reliably after repair, it is important to choose the right rings. Don't buy the cheapest set

Such rings will not last long, and you will have to go through the labor-intensive replacement process again.

It is also important to inspect the packaging and the parts themselves. The packaging must contain all the information about the manufacturer, material of manufacture

The rings must be marked. It denotes the top side. Manufacturers usually include instructions inside the package that tell in detail how to correctly install rings on the piston. The latter should not have any defects, even the smallest ones.

Preparation

So that you don’t have green snot later about the fact that the tuning piston does not fit into the crankcase and you were allegedly deceived here - remove the old piston from the engine and measure the hole for the liner with a caliper. If the hole is smaller than the tuning piston sleeve, the “meat” of the crankcase allows it, hands grow from where it is needed - a round file will help you (only before boring - disassemble the engine, assemble the empty crankcase with bolts, bore the hole, make sure that the piston enters the crankcase without problems - wash the parts from shavings and reassemble the engine. Or, as a last resort, coat the crankcase and file with grease to at least somehow protect yourself from sawdust getting into the inside of the engine.)

The hole for the 162QMK engine sleeve (such engines are installed on Chinese scabs, more popularly known as “Leika”) in stock is 65 mm. Without boring, a piston of 57mm (150CC), 61mm (1700CC) and 62mm (180CC) easily fits into this crankcase. You won’t find a 62mm piston on sale during the day, so it was decided to install a regular 61mm piston on this engine.

By the way, for those who do not know, a piston with a diameter of 61 mm can be easily installed not only on the Leica engine, but also on any other Chinese 150 equipped with a 157QMJ series engine. There, if you put your hands to it, you can stick a piston at 62mm, but only if the “meat” of the crankcase allows it. Everything is individual, you need to look at the place. In any case, the distance along the studs is the same for both the 61mm piston and the 62mm piston.

From left to right: 61mm, 57mm

On the 139QMB series engine from a regular Chinese 80-six, you can easily install a piston 39mm (45CC), 47mm (72CC), 50mm (84CC)

From left to right: 39mm (45CC), 47mm (72CC), 50mm (84CC)

Replacing a piston (CPG) on a 4t scooter

Need help finding spare parts?

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Gradually the time comes and your two-wheeled four-stroke friend needs to change the piston. There may be 2 reasons for this: wear or installation of a more powerful piston. In this article we will tell you how to replace the piston (CPG) on a 4-stroke scooter with a 139QMB engine.

If you have a different engine model, for example 152QMI or 157QMJ (150 cc scooter), then this article will also suit you to replace the CPG, since there are no fundamental differences. For 2-stroke scooters, we recommend reading the article “Replacing the piston on a 2-stroke scooter”

Scooters Maintenance and repair

In this article I will tell you how to change the piston with your own efforts.
In fact, it is not as difficult as it seems. But they are also so simple that anyone could do it, without any specific skills. If you are sure that your piston is already worn out and needs to be replaced, and you want to do it yourself, then let’s get started. Today I will show you an example of replacing a CPG on a Honda Dio scooter, perhaps the most common scooter in our country.

The process of removing the piston.

Firstly, on any scooter, you need to remove the exhaust pipe. It is usually attached with two bolts to the crankcase, and two bolts to the cylinder. On our Honda, to replace the piston, you don’t need to “roll out” the engine. We only remove the toilet and plastic.

We see the engine cooling casing, unscrew the mounting bolts, and remove the casing. Next, unscrew the 4 cylinder mounting bolts, and remove the cylinder head and gasket.

How to repair a chainsaw cylinder block?

To restore, the master completely disassembles the engine and inspects its working parts. Measurements are taken that allow you to accurately assess the condition of the equipment and understand what repair procedures need to be performed. During major repairs, parts can be bored if they are made of materials suitable for this.

The recovery process also includes other stages:

assessing the efficiency of the piston stroke, measuring the compression created in the working chamber;
checking the integrity of equipment, searching for mechanical damage and scratches;
analysis of the condition of piston fasteners, elimination of backlash and other problems;
checking other equipment that affects the operation of the piston group.

In order for the restoration of the chainsaw cylinder to be successful, the master carries out a number of checks after assembling the equipment

It is important that the power corresponds to the factory parameters, and that the saw exhibits stable speed at idle and under load. Only after such checks can equipment repair be considered complete

What to do if wear occurs?

Having discovered that the problem lies in the failure of the cylinder-piston group (CPG), you can use two methods. The first is to purchase the entire CPG, but this option requires large financial investments. However, the owner will not have to waste time searching for a turner on his own and will be able to complete the replacement procedure without outside help.

On the other hand, if you have an original cylinder, it becomes possible to bore the worn-out one using turning equipment. The procedure is as follows: the owner takes the old cylinder with him to the turner. The specialist visually assesses the condition, after which he indicates the repair size. There are four in total:

0.25
0.5
0.75
1.0

These numbers indicate an increase in millimeters to the existing diameter. This amount of metal is ground down during the processing of the inner walls of the cylinder. When boring, the coefficient of thermal expansion of the metal that occurs during engine operation must be taken into account. Therefore, another fifth hundredth of a millimeter (0.05) is added to the indicated number. This will not affect the compression level in any way, and the power unit will not receive a temperature wedge. After assessing the bore diameter, you will have to buy a repair piston. Having purchased it, they pass it along with the cylinder to the master for boring.

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