How to Change a Piston Correctly on a Trimmer

During the operation of the scooter, various breakdowns occur. In this case, it does not matter who the manufacturer is (Japan or China). The difference is that one transport used to fail, and the other over time. Malfunctions can occur with wiring, engine, chassis. But, as a rule, almost all are faced with the replacement of the CPG. This abbreviation implies the term “cylinder-piston-group” or, as is commonly called, “piston”. Looking ahead, it is necessary to say that replacing a piston, a piston and rings individually is not as difficult as it might seem at first glance. It is also worth knowing that the process of removing and replacing a CPG is almost the same on all scooters. Therefore, the article will consider the main points. Looking ahead, we recall that the power of the CPG can vary. It is recommended to install a piston of the same power as a standard CPG.

How to Change a Piston Correctly on a Trimmer

Preparatory moments

Before replacing a piston or rings (combined cylinder head), you need to get to the cylinder. For beginners who have no idea where this element is located, let’s tell you. The muffler is just bolted to the cylinder. In case you have no idea how to put the piston on a 4t or 2t scooter, then first you need to remove the old CPG. Upcoming repairs can be divided into the following steps:

  • Removing the scooter lining (plastic);
  • Disconnecting electrical wires;
  • Disconnecting the hose with oil;
  • Engine dismantling;
  • Removing the old piston rings (CPG in the aggregate);
  • Installation of new parts;
  • Mounting the engine, connecting wires and a hose;
  • Plastic fasteners.

The plastic is folded to the side so as not to crush if careless. All bolts and cogs are put in a pile, if necessary, sorted separately. After making sure that all hoses with gasoline and oil are disconnected, remove the engine. You must understand that removing the engine differs depending on the design features of the scooter model. Once the engine has been removed, you can begin to remove the plastic casing, which protects the CPG from external factors. Then remove the cylinder head. It is mounted on 4 bolts. In order not to break the thread, all the bolts unscrew the cross to the cross.

We remove the cylinder and immediately inspect it. If there is no damage, then it can continue to be used. While the piston is most likely not to be reused.

How to put the piston on a scooter

The new piston is equipped with a finger, two retaining rings and additional rings. If the scooter is 2-stroke, then the number of additional rings is 2. In 4-stroke, 3 rings are almost always installed, one of which is oil scraper. Consider installing a piston and rings using a 2-stroke scooter as an example. First, two compression rings are put on the piston, in special grooves. Next, with the so-called “finger” we connect the piston and crankshaft, the fasteners are considered to be complete after installing 2 retaining rings on both sides of the finger. The rings should fit tightly in the holes provided. Remember: the arrow on the piston should look down, at the floor. The above-described “processes” are not complicated, if you look. It’s best to watch the training video or read the scooter maintenance manual. Then certainly there will be no questions like “How to put rings on the piston of a scooter”.

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Cylinder installation

The final stage and it should be treated with caution. After all, with improper fasteners, the slightest clearance will not be necessary compression. As a result, the scooter will not start. Install a gasket between the engine and the cylinder, as well as between the cylinder and its head. The head is clamped bolt cross to cross. Checking for correct work is easy. To do this, start the engine. If the motor runs smoothly, everything is done right. You can also make a few kick-starter efforts for a sense of compression.

As you have already killed, there is nothing complicated. The installation of rings on the piston of the scooter, the replacement of the CPG in the aggregate does not require special knowledge. Only details, time and desire are needed.

During the operation of the scooter, various breakdowns occur. In this case, it does not matter who the manufacturer is (Japan or China). The difference is that one transport used to fail, and the other over time. Malfunctions can occur with wiring, engine, chassis. But, as a rule, almost all are faced with the replacement of the CPG. This abbreviation implies the term “cylinder-piston-group” or, as is commonly called, “piston”. Looking ahead, it is necessary to say that replacing a piston, a piston and rings individually is not as difficult as it might seem at first glance. It is also worth knowing that the process of removing and replacing a CPG is almost the same on all scooters. Therefore, the article will consider the main points. Looking ahead, we recall that the power of the CPG can vary. It is recommended to install a piston of the same power as a standard CPG.

Preparatory moments

Before replacing a piston or rings (combined cylinder head), you need to get to the cylinder. For beginners who have no idea where this element is located, let’s tell you. The muffler is just bolted to the cylinder. In case you have no idea how to put the piston on a 4t or 2t scooter, then first you need to remove the old CPG. Upcoming repairs can be divided into the following steps:

Video: How to Change a Piston Correctly on a Trimmer


  • Removing the scooter lining (plastic);
  • Disconnecting electrical wires;
  • Disconnecting the hose with oil;
  • Engine dismantling;
  • Removing the old piston rings (CPG in the aggregate);
  • Installation of new parts;
  • Mounting the engine, connecting wires and a hose;
  • Plastic fasteners.

The plastic is folded to the side so as not to crush if careless. All bolts and cogs are put in a pile, if necessary, sorted separately. After making sure that all hoses with gasoline and oil are disconnected, remove the engine. You must understand that removing the engine differs depending on the design features of the scooter model. Once the engine has been removed, you can begin to remove the plastic casing, which protects the CPG from external factors. Then remove the cylinder head. It is mounted on 4 bolts. In order not to break the thread, all the bolts unscrew the cross to the cross.

We remove the cylinder and immediately inspect it. If there is no damage, then it can continue to be used. While the piston is most likely not to be reused.

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How to put the piston on a scooter

The new piston is equipped with a finger, two retaining rings and additional rings. If the scooter is 2-stroke, then the number of additional rings is 2. In 4-stroke, 3 rings are almost always installed, one of which is oil scraper. Consider installing a piston and rings using a 2-stroke scooter as an example. First, two compression rings are put on the piston, in special grooves. Next, we connect the piston and crankshaft with the so-called “finger”, the fasteners are considered to be full-fledged after installing 2 retaining rings on both sides of the finger. The rings should fit tightly in the holes provided. Remember: the arrow on the piston should look down, at the floor. The above-described “processes” are not complicated, if you look. It’s best to watch the training video or read the scooter maintenance manual. Then there certainly will not be questions like “How to put rings on the piston of a scooter.”

Cylinder installation

The final stage and it should be treated with caution. After all, with improper fasteners, the slightest clearance will not be necessary compression. As a result, the scooter will not start. Install a gasket between the engine and the cylinder, as well as between the cylinder and its head. The head is clamped bolt cross to cross. Checking for correct work is easy. To do this, start the engine. If the motor runs smoothly, everything is done right. You can also make a few kick-starter efforts for a sense of compression.

As you have already killed, there is nothing complicated. The installation of rings on the piston of the scooter, the replacement of the CPG in the aggregate does not require special knowledge. Only details, time and desire are needed.

One of the most serious scooter failures is the failure of the cylinder-piston group, which immediately makes the scooter inoperative. It is the CPG of the scooter that is responsible for its movement, the slightest damage will lead to the impossibility of further movement. That is why if you encounter a non-working piston, immediately take care of its repair.

In general, any CPG has a certain lifespan, with a certain mileage its wear increases and the buyer will have to replace the part. Often enough to replace the piston, but sometimes more serious problems occur. Where you have to change the piston, rings and cylinder. Depending on the model of scooter and manufacturer, the installation may be slightly different, but we will consider the basic steps. Also, piston scooters may vary in power, but this does not affect the replacement process.

CPG removal

If you don’t know how to properly install the piston on a 2t or 4t scooter, first remove the old part. To get to the piston group is not easy, you have to disassemble the scooter, and sometimes remove the plastic. In general, the steps to replace the CPG are as follows:

  1. Removing the engine, disconnecting the wires;
  2. Removing the old piston;
  3. Installation of a new part as required;
  4. Similar assembly of the engine and the connection of electrics and hoses.

After you have disconnected all wiring and made sure that the oil and benzo hose are closed, remove the engine. In different scooter models, the removal of the engine may be different, so proceed according to the situation. Having received the finished engine, start to remove the plastic cylinder cover, it protects the CPG from external dirt, dust, etc. The next step is to remove the cylinder head. Depending on the type of scooter (2t or 4t), the head can be more complex, 4t scooters also have valves, which will then have to be adjusted. But the procedure for removing the head occurs by loosening 4 nuts.

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Important: The nuts must be loosened gradually using a cross-wise method. That is, as shown in the picture below. Otherwise, you will break the threads and the piston will be damaged. This also applies to the installation of a piston, the nuts are tightened as well.

Then you have to remove the cylinder, in some cases it is problematic to do this due to the large formation of soot or a piston defect. If the cylinder is whole, but the piston is defective, proceed to replacing the piston. How to install the piston on a scooter

Replacing the piston involves a number of difficulties, because the piston will come with a few more basic parts. In the kit you will find snap rings, a finger and several rings (depending on the scooter. 2t or 4t). In 2-stroke scooters, they usually put only two rings, they are compression, the third thin ring is practically not necessary, but we recommend placing it under the lower ring for springing. In the case of 4-stroke mopeds there are three main rings, two of them are compression, the third is oil scraper.

The assembly of rings is presented on the basis of a 2t scooter, it has a simpler design. So, put the two rings on the piston, then take your finger and insert it into the crankshaft hole so that the piston holds firmly. Be sure to secure the finger with retaining rings on both sides, this is necessary so that the finger does not come out during operation. Also, the snap rings should not stick out, they should lie tightly in a special hole. Important: you need to install the piston exactly with the arrow (or EX inscription) to the exhaust pipe, otherwise the whole procedure will be useless. The next step is to install the cylinder on the piston.

Cylinder installation

This procedure is quite complicated, because putting the cylinder on the piston is ideal. First of all, do not forget to put gaskets on both sides, they are both included with the CPG, and are bought separately. There are usually two gaskets, one placed down between the cylinder and the engine, the second is installed between the cylinder and the head. After installing the lower gasket, try to put on the cylinder so that the rings meet in the groove. To do this, during the installation of the cylinder, it is enough to press the rings, after lubricating the cylinder and piston with oil.

Then put on the gasket and fix the head with nuts. Tighten the nuts in a cross order. After that, check the piston’s kickstarter operation, if the installation is successful, the piston should walk along the cylinder evenly and have noticeable compression.

That’s all, reassemble the scooter in the reverse order, connect all wires and hoses.