Replacing the Piston on the Partner 350 Chainsaw

Repairing a Partner 371 chainsaw with your own hands video

A chainsaw, like any device powered by an internal combustion engine, has an ignition system. It is responsible for igniting the air-fuel mixture in the engine cylinder. This occurs through the delivery of an electric discharge, which pierces the space between the electrodes of the spark plug.

It’s clear that without ignition, no engine will start or run. But that is not the only problem: the chainsaw’s performance depends on how accurately the ignition is set. In other words. timely or untimely ignition of fuel. That’s why a chainsaw with a knocked down setting needs to be repaired. Troubleshooting can be entrusted to an experienced mechanic, but you can repair your chainsaw’s ignition with your own hands.

Some Chinese chain saws come with low-quality spark plugs. it may make sense to have a few spark plugs in the kit.In our review, we will introduce you to the device and the principle of the ignition system, its main faults and ways to fix them.

often than not we think about the repair after the chain saw has stopped starting or there are visual signs of serious malfunctions.

If the chainsaw won’t start, you need to do a step-by-step diagnosis. It is recommended to go from simple to complex and to do everything in order. Although the devices differ from manufacturer to manufacturer, the working principle and layout are the same: the basis is a two-stroke gasoline engine, which through a gearbox turns a tensioned cutting chain.

The diagnosis must be made one after the other:

Checking the electrical system (whether there is a spark on the spark plug electrodes or not).

Each of the four steps should be considered separately.

  • A set of car wrenches, a screwdriver, and sockets.
  • Screwdrivers: Phillips and slotted screwdrivers, flat-tipped spatulas for cleaning parts.
  • Metal brush (cordbrush) and brushes with stiff bristles.
  • A basin for washing parts (a cut off plastic canister will do).

It is recommended to use a compressor to blow out the engine parts. Do not use industrial gases (especially oxygen).


If the chain saw has been in operation for a long time, the air or fuel filter could be clogged. If the former do not get the right amount of air into the cylinders, the fuel mixture will not combust. If the fuel system is clogged, the gasoline mixture will stop flowing.

Air-cleaning element should be removed carefully, the dust should not get into the carburetor. It should be blown and washed with soap and water, dried and put back in the same way.

To check the condition of the fuel filter you need to remove the hose from the carburetor, try to pump fuel manually. If the trickle is too weak or completely gone, you need to replace or flush the filter. You can buy a new one from your dealer, or go to a power tool repair shop.

Check spark plug

It might be necessary to install new spark plugs

The operation is similar to that performed by all motorists with gasoline engines. If you have a new and 100% functional spark plug in stock, the easiest way is to put it on and try to start the chain saw. Inspect the old one: Heavy soot indicates that the engine is not running properly.

  • Remove the high voltage lead.
  • Unscrew the spark plug and reattach the wire that was removed before.
  • Lean the “skirt” of the spark plug against the unpainted part of the cylinder.
  • Try to start the engine.

The spark must be bright. Dull indicates that either the wire itself does not conduct enough current, or it is time to throw the plug away, or the ignition unit. the magneto, which distributes the charges to the cylinders according to the engine stroke. is defective.

You can try to disassemble the ignition unit, clean the contacts, dry it, assemble it and try again. A number of faults cannot be eliminated, so in some cases the block will need to be replaced, but this is a last resort.

For the beginning it is required to prepare a workplace:

  • Remove dirt and dust from the workbench.
  • Prepare a clean rag, brushes, and containers for washing small parts.
  • If there is a compressor, prepare it to blow the carburetor channels.

The chainsaw itself should be cleaned and blown with compressed air. Now you can proceed with the diagnostics.

  • Fuel tank. inside there should be no dirt, iron filings, sand and other impurities.
  • the breather valve built into the cap. air must enter the tank through it, otherwise it will create a vacuum during operation and the fuel will not enter the carburetor.
  • Check hoses and tubes for cracks or other defects. If any suspicion is suspected, replace.

After assembly it is required to check: if as a result of manual priming with the feeding tube removed from the carburetor the gasoline mixture goes in a tight stream with jerks, then the system is serviceable. If your chain saw still won’t start, it’s the carburetor’s fault.

Pay attention to the mixture quality. It is not recommended to leave the gasoline in the tank for a long time after work, it is better to pour it into a separate container and then dilute it with fresh fuel. Otherwise, when using an old (14 days or more) mixture will release harmful substances that will be deposited on the surfaces of the elements of the piston system of the engine.

Exhaust ports

You may need to clean the exhaust passages on the chainsaw

After long time of use the chain saw could get corked in the exhaust pipes and that is why the forward motion of the piston is blocked. Simply put, unremoved gases slow the engine down.

  • Remove the chainsaw muffler.
  • Remove the gasket carefully.
  • Dismantle spark arrester.
  • If possible disassemble the resonator body.
  • Clean parts with detergent solutions (kerosene, WD-40) and mechanically.
  • Wipe and dry components.
  • Reassemble the system.


In most cases the following problems occur in engine operation

  • The engine stops starting;
  • The engine starts but stops after a while;
  • engine is not able to develop the necessary power;
  • The engine runs extremely erratically.

How to check the crankshaft oil seals

The presence of leaking oil seals can only be checked by getting to the crankshaft itself, and carefully examining it for leaks. About how to do it correctly, you can read on

How to check compression on a chainsaw

At a level of compression below 8 atmospheres the engine will not have enough power, and therefore the chainsaw will not be able to function fully.

  • Remove the protective cap and unscrew the spark plug.
  • Insert the tip of the compression gauge into the hole where the spark plug should be located.
  • Using the starter cord, give the piston rotation and memorize the maximum reading of the measuring device.
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How to put the piston on the chainsaw correctly

Work on the replacement of the piston for most models of modern chainsaws is carried out according to the following algorithm:

  • The top and side covers are removed.
  • The spark plug is unscrewed.
  • Stoppers are removed from the shock absorbers and the handle is disconnected from the body.
  • Remove the drive sprocket and starter motor.
  • A piston stopper is installed in the spark plug hole and the nut securing the flywheel and clutch is unscrewed.
  • Remove the flywheel, clutch, and oil pump worm drive, located right behind the clutch mechanism.
  • The screws that fasten the carburetor and air filter are loosened, and then these assemblies are removed along with the motor control lever.
  • The ignition coil and the muffler are removed.
  • The saw is turned over with the bottom up and, having removed the screws to the body, disconnects the engine.
  • Unscrew the pallet and remove the piston.
  • Since the piston is removed only together with the crankshaft, it is necessary to remove the retaining rings to disconnect it.
  • The old piston is replaced with a new one, but as carefully as possible. this is caused by the high brittleness of the compression rings.
  • The crankcase is put in place and a sealant is used in place of the gasket.

All subsequent actions are carried out according to the algorithm, the reverse of disassembly.

How to prevent the chainsaw from breaking

Repair of chain saw in some cases can be very expensive. This can be avoided if enough attention is paid to preventive maintenance and control the condition of the tool and all its parts. Especially since this condition is not difficult to fulfill. it is enough to use the operating instructions and to adhere to rational accuracy:

To keep it in working order, you just need to follow the instructions carefully and follow some general rules:

  • Do not overheat the engine, let it rest and cool down.
  • Do not overload the chainsaw by overloading it. For example, if you are using a Partner 350 utility class saw, it is simply not designed to run for more than 40 minutes a day.
  • Check the serviceability of the chain brake daily (this is done at maximum acceleration).
  • Follow the manufacturer’s instructions regarding the quality, composition of the fuel mixture.
  • Check the spark plug condition weekly and clean the electrodes as needed.
  • Before using your chain saw, make sure the chain is sharpened and installed correctly. Watch out for wear on the cutting links and sharpen them in good time. Watch out for cracks and tears in the rivets.
  • A properly tensioned chain does not sag, but you can move it with your hands. Never do this with a hot chain! Sharpen and/or retighten it after changing.
  • When filling up your chain saw, make sure no dirt or other foreign material enters the tank along with the fuel. Fill oil and gasoline carefully and do not spill them.

It’s not uncommon to find that a Partner chain saw breaks down because it’s not started correctly when you call the service center. So there’s only one universal solution to a broken chain saw: handle it right and you’ll avoid most problems.

If you’re interested in why STIHL chain saws, the second most popular brand in partnership with Partner, break down your saw, read the following article.

And for those who like to know more, here is a video on how to repair a Partner chain saw

The Partner 350 chain saw is one of the most common gasoline-powered saws. It’s not unusual for owners to have questions about how to fix their Partner 350. After reading this article, you’ll learn the answers to how to diagnose Partner malfunctions and how to fix them yourself.


Several special tools are required to disassemble your Partner 350:

  • A clutch wrench (you can buy one or make one yourself out of a socket of the right size).
  • Plunger stop.
  • Torx hex driver set.
  • Soft metal hammer.

For simple disassembly of the Partner 350 you will need tweezers and a medical clamp. Of the usual tools you need to have a screwdriver or a cordless drill with a set of tools, a hammer.


Before you start adjusting the carburetor of the “Partner-350” chain saw, you need to study the construction of the unit in all the details. Since it is used practically unchanged in many models, the recommendations below are valid for the vast majority of them.

When removing the elements, you should be as careful as possible, laying them out in the same order in which they were dismantled. This will make later reassembly easier. The top cover is held by three bolts and must be removed. After that you will see a layer of foam rubber, which serves as an element of the air filter. To remove the actuator rod, you need to get rid of the gasoline hose. To perform the adjustment of the carburetor of the “Partner-350” chainsaw can not be made without removing the tip of the cable, this must be done in the following step. The fuel hose that is on the left side of the connector should be removed. After completing all the above procedures, you can disconnect the carburetor and proceed to its adjustment. This mechanism is very complex, for this reason, during the subsequent disassembly, you must be extremely careful when removing parts. Without it, they are easy to lose because of their small size.

Characteristics of Partur 350 chain saw

This model is in great demand among customers, but most often it is bought by gardeners for works on their plots. the saw is used not only for making firewood, but also in construction.

In general, the Partner 350 chain saws are characterized by their compact size. They are equipped with a powerful enough engine. Their main advantages are easy start and reliable performance

, an electronic ignition system and a fuel pump of high quality.

It is absolutely safe to use such a chainsaw. It has a built-in safety system that automatically starts the parking brake

for the chain. The same mode is used for its lubrication.

No problem with starting the Partur chainsaw even in winter, as it has a fuel primer

The starter drum is equipped with an impeller that helps clean the dirt. The tool is also equipped with the CCS system. This design retains particle abandonment and is also used when the air filter is used for extended periods of time.

To extend the life of the chainsaw, the chain saw’s cylinder piston group has chrome-plated walls

This model also has an ergonomically designed handle and anti-vibration system.

Sprocket replacement

The most common cause of faults in this element is chain jamming due to chain skew or considerable wear of the chain saw sprocket itself. If there are any signs of these deviations, it is necessary to carefully inspect the plane and teeth of the drive transmission element, paying attention to the depth of drift (it should not exceed 0.5 mm).

If there is heavy wear or deformation on the sprocket housing it can sometimes be repaired, but if it is too bad it needs to be replaced. Regardless of the nature of the damage found, before repairing it will first be necessary to remove the sprocket from the chainsaw, that is, completely free it from all holding fasteners.

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Note! To gain access to the sprocket, you will have to disassemble the entire drive unit of the working mechanism, including the air filter, clutch basket, and more.

Most chainsaws have a clutch that is the same way. For disassembly, you should use a spark plug wrench, which is usually included with the chainsaw, a clutch puller and a piston stopper.

First unscrew and remove the bar and remove the chain. Remove the top cover to gain access to the spark plug, unscrew it and install the piston stopper. Often a rope or string is used for the stopper, but experts advise against it. It is better to use a special stopper to remove the clutch. Remove side cover, unscrew clutch (clockwise!) and get to the sprocket.

In the other variant unscrew the starter and remove protection to hold from the back side of the assembly, which scrolls. The order of complete disassembly of the main parts of the chainsaw is well presented in the video

All removed parts should be stacked in one place so they don’t get lost. It is possible to take pictures of chain saw assemblies in order to quickly assemble the tool in the reverse order after the repair.

Signs of a faulty lubrication system

The right choice of consumable lubricant and flawless operation of the system, contribute to full lubrication, effective cooling of the saw equipment and the full working out of its resource.

There are several outward signs that the chain on a chainsaw is not lubricated. Above all:

  • Constant oil level in the reservoir;
  • increased load on the engine;
  • Accelerated wear on the cutting edges of the saw links;
  • A characteristic smell of overheated wood.

In the simplest case, the cause of oil starvation can be clogged with sawdust in the oil ducts. This disadvantage is typical for budget headsets that do not have convenient access to the problem areas.

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Adjusting the carburetor on your Partner 350 with your hands

Before you start adjusting your Partner’s original carburetor, you must first carefully remove any dust, dirt, and carbon buildup from the carburetor. In addition to the carburetor, you need to wash and dry the fuel and air filters. Otherwise the operator will not be able to set required engine RPM accurately.

On the upper left side of the protective plastic housing of your Partner there are holes in which the manufacturer provides screws for adjusting the carburetor. Having found them, you may proceed to basic setting of the unit. To do this, the left and right screws, which are responsible for the number and quality of revolutions, respectively, must be set in the fully screwed position. Immediately after that, loosen them by 1/5 of a turn. The third adjusting bolt, marked with a T, must be left in the position in which it is installed.

Perform the final carburetor adjustment on the Partner 350 in the following order:

  • Start the chain saw and let it run through its power to warm it up completely;
  • After about 5 minutes you can begin to adjust the carburetor. First turn the left adjusting screw in the direction of the hand of the clock until the motor reaches maximum rpm. Then it is necessary to turn the left adjusting bolt by 1,4 turns in the opposite direction. After completing these steps, your Partner chainsaw engine should run smoothly at idle speed;
  • If, after manipulating the left adjusting screw, the chain on the bar begins to rotate, it must be stopped by alternately turning the T bolt;
  • Then it is necessary to proceed to the adjustment of the fuel mixture quality. To do this, the right adjusting screw must be turned in the direction of the arrow. As soon as the engine has reached the maximum allowable rpm, the screw should be turned back by 1/4 turn.

When adjusting the maximum engine speed of your Partner 350 saw it is best to use a tachometer connected to the motor beforehand. As soon as the gauge shows the same RPMs as the model’s instruction manual says, it means that turning the screw should be stopped.

READ Hands-On Planter for Ural Benzosaw

Algorithm and description of the disassembly process

If you want to completely disassemble your Partner 350 chain saw, the first thing to do is to clean it with a compressor. Next, the chainsaw assemblies are removed in the following order:

After the first stage of disassembly is over, we clean the chainsaw again with a compressor, t. к. There is already access to the air ducts, which in most cases are heavily contaminated with wood dust.

The next step is conveniently to remove the air filter housing and carburetor of the Partner 350.

After removing the carburetor, the cylinder intake window should be plugged with a rag, it will prevent foreign objects from getting into the engine crankcase.

The muffler can be removed after you remove the carburetor or after you remove the engine. The exhaust port is also covered with a rag.

This requires the use of a piston stopper, placing it in the spark plug hole.

The clutch on all Partner 350 chain saws unscrew the clutch during chain rotation to prevent the chain from unscrewing during operation. The flywheel nut has a standard thread and can be unscrewed by turning it counterclockwise with a 13-mm screwdriver.

Once the clutch is removed, you will have access to the oil pump and it too must be removed.

Reassembling your Partner 350

In order to properly reassemble your Partner 350, you must install all items in the reverse order of removal.

If this is the first time you have tried to repair a Partner 350 chain saw, make sure to disassemble the parts in the same order you removed them. This helps prevent confusion and forgetting to install any of the parts.

An important feature in assembling a Partner 350 chain saw engine is that the crankcase cover is installed without a gasket. Instead of it, red sealant is used, which is applied in a thin layer to the place where the crankcase is installed. Before applying the sealant, it is necessary to degrease the crankcase cover and the place where it is installed, for better adhesion of the sealant.

Adjusting the Flywheel and Coil Gap (Ignition Adjustment)

While reassembling the Partner 350 chain saw, if you removed not only the flywheel, but also the ignition coil, you need to adjust the gap between them. To do this, first you install the flywheel, then lay a piece of a half-liter plastic bottle on it, and then put the coil and fixed the two mounting screws, while the flywheel should be turned to the coil magnetic contacts.

After adjusting the clearance, turn the flywheel. If it does not touch the coil pins, the gap is set correctly.

Adjusting the Partner 350 chain saw

Before starting your Partner 350 chain saw, it is specially prepared according to the instruction manual, and this includes

  • installing the saw headset or checking its tension for parts that are already installed;
  • checking that the brake band is in good condition;
  • Getting the brake lever ready as shown in the illustration;
  • filling the oiler and the gas tank with fuel and lubricants. The fuel mixture is made in the 1:50 proportion from the oil for 2-stroke engines and unleaded gasoline AI-92.
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Start-up is carried out on a level surface, sharply pulling the throttle cable. When starting cold, open the choke shutter and let the chain saw warm up. Only after that can you pick up the speed and move on to woodworking.

All possible nuances of the adjustment of the Partner 350 chain saw with your own hands are described in detail in the instruction manual. If they are not observed, the tool is not immune to malfunctions and repairs, the budget of which can be unpredictable.

Knowing how much a carburetor costs on a Partner 350 chain saw, any owner of this saw, before replacing the unit completely, tries to repair and adjust it himself. Often such repairs lead to the complete destruction of the carburetor, and in the case of the adjustment, the death of the engine. To avoid such problems it is necessary to become familiar with the repair and adjustment process in advance, but the best option is to entrust the repair and adjustment of the carburetor of the Partner 350 chainsaw to professionals.

Your Partner 350 chain saw has a standardized carburetor. Exactly the same carburetors can be found on other brands of chainsaws with similar power. They are made by several manufacturers, but the design, dimensions and parameters of these products are standardized.

What kind of carburetor is used on the Partner 350 chain saw?

The Partner 350 chain saws use carburetors made by Walbro, Japan, which is the world’s largest maker of fuel components for gasoline-powered machines.

A specialized company that is constantly working to improve the design and quality of its products and values its reputation.

The body of the carburetor from this company has the Walbro lettering molded in large letters, and there is a product number. If it is not marked, it means that your Partner 350 chain saw has exactly the same carburetor but from a different, lesser-known maker. In Russia you can find Partner 350 chain saws both with Walbro carburetors and with unmarked products. By design and operating parameters they are identical.

Principle and construction of the Partner 350 carburetor

The carburetor draws fuel from the gas tank, atomizes it in the nozzle-diffuser and pumps the fuel-air mixture into the combustion chamber.

The fuel flow from the tank to the carburetor reservoir is metered by a diaphragm, which opens and closes the needle valve. A calibrated orifice in the nozzle and adjusting screws meter fuel flow from the carburetor into the combustion chamber.

The engine speed depends on the quantity of fuel-air mixture that enters the combustion chamber. This quantity is adjusted during operation, by the throttle valve, which opens when the throttle grip is pulled, and vice versa.

The air damper regulates the air supply from the air filter. It is closed during cold start, which makes it easier to start the engine. When the throttle trigger is pulled, the throttle valve opens.

There is an idle mode for operation, when a minimum amount of fuel mixture enters the combustion chamber without pushing the throttle knob.

To start a cold engine, the carburetor has a manual primer pump (suction). Basic carburetor assemblies:

  • housing, it contains the storage tank, the fuel and air passages, and all the parts;
  • throttle and air flap;
  • elastic diaphragm;
  • the crossover with a needle valve;
  • jets with a calibrated hole;
  • diffuser, fuel spray nozzle;
  • The three adjusting screws T, H, and L.

This is what the original carburetor looks like on a Partner 350 chain saw

Screwdriver points to the nozzle valve

Recommended solutions for common problems

The Partner 350 has popular malfunctions that owners of these saws can diagnose and repair themselves. Let’s take a closer look at popular malfunctions and how to fix them with your hands.

Stopping on the gas

If your Partner 350 stalls on the gas, there is likely a problem with the fuel system. The most common problem is a carburetor misfire or improperly adjusted carburetor, or an air bleed.

Tip: If your chainsaw stalls when you increase the RPM, don’t immediately adjust the carburetor. Start by checking the engine for air intake. One of the signs of a leaking air supply is a prolonged idle stroke.

It starts and stops

If your Partner 350 starts up and shuts down, there are several possible causes, but the most common is an overinflated fuel supply. You should start troubleshooting by checking the condition of the fuel filter and lines. If the fuel is coming in normally, then check the spark and try to start the chainsaw on a new spark plug, t. к. The chain saw may be shutting down because of an interruption in the spark formation.

You should also check the choke linkage. If it does not open the choke or does not open it fully, the engine could shut down from over-enriched fuel.

No chain lubrication

There are a few reasons for the lack of lubrication on your Partner 350 chain saw and here we can list them all.

How to solve oil pump problems described above.


A very common problem faced by owners of a Partner 350. The first place to start checking is to replace the spark plug with a known good one. If it did not help, the spark is good, but the engine is flooding, then the cause is hidden in the settings of the carburetor. To learn how to diagnose and tune a carburetor on your Partner 350, visit our website.


If oil is getting to the chain in excessive amounts, not only when the saw is running but also when idling, adjust manually (if the pump is designed to do so). This is done by means of the screw located on the housing near the guide bar, usually at the bottom or side. Tightening the screw reduces the oil flow and loosening the screw reduces the oil flow. If adjustment does not help check the pump and the guide bar may be loose and leaking oil from the chain at the connection to the chassis.

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Lack of oil can be caused by several reasons, each of which has its own solution:

  • Malfunction of the oil pump. It usually consists of a bad gasket. In order to replace it, the pump must be carefully disassembled to avoid damaging its moving parts. Next, a new gasket is installed, after which the pump is assembled and reinstalled.
  • Breakage of the oil hose. In case the pump gasket is serviceable, or its replacement has no result, it is necessary to check the hose tightness. If it is defective, it must be replaced. Otherwise it is not superfluous to clean it and fix it with sealant.

If the cause is not a pump malfunction, all passages and passages should be checked for blockages and if necessary cleaned of foreign matter. This can be done with a jet of compressed air.

Don’t want to mess with the chainsaw, but need to adjust the oil flow? Ask our specialists to help you to diagnose and repair your chain saw and, if necessary, make repairs and adjust the lubrication level. Your saw is as good as new!