Gap on trimmer between spool and handwheel

About chainsaw and its inoperability

Chainsaw. the installation itself is not so complicated. But to have the least initial knowledge is extremely important to find and fix any defect.

Modern electronics have progressed so much that they have revolutionized the tool world as well. Today’s saws are lightweight and powerful at the same time and have electronic ignition systems.

Not so long ago, saw ignition systems were cam. This carried with it a host of disadvantages: heavy, complicated, expensive, and more. And the most important disadvantage of the archaic ignition system is the difficulty of starting. Some saw model systems could not produce a spark at all, enough to flash at the crankshaft speed.

Modern systems are almost failsafe. The saw models are lightweight and rugged, the coil is built more professionally and lasts almost non-stop. There are problems, however, but they can usually be fixed by your own efforts.

Let’s look at the main types of chainsaw malfunctions related to the flywheel and ignition system.

As a rule, the most common ailment of modern chainsaws, involves a lack of supply spark. The same is directly related to the shift in clearance (clearance) between the drum and the flywheel.

Common installation failures are always related to the internal combustion engine. The problems arise in the ignition system, the fuel intake module, in the internal elements of the engine itself.

As for the other nodes of the chainsaw, the malfunctions there are usually due to failures of the brake mechanism, poor operation of lubrication, etc.д.

If starting difficulties are related to the engine, these symptoms are the most common:

As always, experts recommend identifying fault factors by the method of elimination. In other words, it is necessary to go through the chain, diagnosing each node, each link.

trimmer, spool

Ignition module

Failure of the chainsaw NW is the most common reason why the engine of the tool does not start. It is recommended in most cases to start troubleshooting from here.


  • First of all carefully check the spark plug, carefully removing the armored wire from the head and unscrewing the spark plug from its seat with a special key;
  • The second is to check the spark supply by jerking the starter with the armature cap on the spark plug;
  • Checking the gap is the main subject of our article (more below).

So, the malfunction of the spark plug will clearly indicate its wetness. Wet spark device for ignition of the fuel-air mixture indicates that the system has too much fuel, the carburetor is not properly set, or there are problems in the NW.

The spark plug is only checked after it has dried out. Т.е., it is necessary to clean it well with a napkin, dry the internal combustion engine, plug the supply, and then crank up the starter a couple of times to get the excess combustible mixture out.

Then the spark plug is put back in place, and everything is checked again.

In general, a spark device can tell you a lot about the whole ignition system. If black soot is observed on the spark plug, it indicates a disturbance in the communications of the gasoline mixture. Either the petrol to oil ratio is faulty or the carburettor needs to be readjusted. In some cases it also happens because of low-quality oil.

A dirty spark plug is cleaned of black carbon deposits with a needle or other sharp object. Then the electrode is cleaned with sandpaper (null sandpaper) until a metallic sheen appears. The sparking device is put back in place, and everything is rechecked.

Next step: check the spark feeder. The spark plug skirt is brought to the cylinder and the starter starts. If there is a bluish spark at a distance of 2-3 mm, everything is normal. The spark gap of 0.5-1 mm is already considered as a malfunction. There may be no spark at all, and this is also a big problem. It might be a broken wire.

And here we come to the subject of our article. The chain saw can fail to start because of the gap between the ignition and the flywheel magneto. This very gap should be within 0.2 mm. Checked very simply: a special gasket is placed between the flywheel and the spool. If it works fine, not too loose and tight, the gap is normal.

The saw flywheel itself is round, and checking the gap with an ordinary dipstick is not possible. It would be more skilled to put a gap on a special template, however it is not always possible to get it. Not everyone can afford to buy an expensive template for a single use.

But instead of the foreign gauge, you can use a cut out strip from a 1-2 liter plastic juice bottle.

Tip. It’s a good idea to cut the plastic strip where there are no ridges.

Clearance between the ignition coil and the chainsaw flywheel

Modern chainsaw

ICE engines are not only installed on cars or motorcycles. They are also widely used in various tools, such as a chainsaw or grass trimmer. If they are faulty and the ignition is poorly started, it is often sufficient to have the right gap between the flywheel and the ignition coil.

How to correctly set the ignition on the trimmer: adjusting the gap between the magneto and the flywheel

Gasoline trimmers use both two-stroke internal combustion engines (ICE) and four-stroke. But the ignition system in them does not differ from each other, so the repair and adjustment of this system of fuel ignition will be the same for different types of ICE.

How the ignition system on the trimmer works

The ignition system of two-stroke ICE consists of 2 elements: flywheel and coil (magneto). The illustration below shows what they look like.

On the flywheel there is an impeller which functions as a fan for cooling the engine. Also on one side of the flywheel are permanent magnets, shown with an arrow in the figure.

As the flywheel rotates, the coil generates electric current in the coil, which serves to produce a spark on the spark plug. The spark appears at the moment when the magnets are directly under the magneto.

See also  How To Remove The Coil From The Patriot Trimmer

Why do you need an ignition timing adjustment?

In some cases, when the engine does not start, it will be necessary to adjust the ignition. Of course you first have to check that the spark plug, the high-voltage cable and the cap are working properly.

It is necessary to adjust the ignition on a two-stroke engine in order to ensure timely ignition of fuel in the engine combustion chamber. Below is a diagram, from which you can understand the principle of operation of the internal combustion engine.

the spark should appear at the moment the piston compresses the fuel, when it is just a short distance from the top dead center (TDC). When the piston passes TDC, the fuel mixture ignites, propelling the piston downward with the energy of the explosion

Therefore, if for any reason (mainly because the flywheel is shifted on the shaft relative to its original position), fuel ignition occurs before the piston passes TDC, it goes back and the crankshaft is cranked in the opposite direction. Such movement can damage the starter assembly, cut the starter cord, etc.д. In this case there is an early ignition of fuel.

It can also be a late ignition on a trimmer: The piston, after compression of fuel that has not ignited, goes down, and at that moment there is a spark. In such a case, the engine either does not start or loses power and picks up speed very badly.

But such problems with early or late ignition on two-stroke engines are quite rare, because the flywheel with magnets is already set in the correct position, which is perfectly synchronized with the movement of the piston. In addition, the flywheel is secured to the shaft with a key and a nut. Therefore, improper installation of the part is ruled out.

Basically, ignition adjustment consists of setting the correct gap between the magneto and the flywheel.

How to check if the magneto is working properly

The magneto is the main part in the engine ignition system and is the coil with the primary and secondary windings around the core. The spark is often lost on the spark plug because of a magneto failure and the propellant fails to ignite. To check the coil, you will need to use a tester, and perform the following steps.

  • On the tester, having switched to resistance measurement mode, you must set 200 ohms. Use this to check the primary winding.
  • Connect one electrode of the tester to the “mass” of the coil and the second one to the contact going out of the magneto. In the norm, the resistance should be from 0.4 to 2 ohms.
  • To check the secondary winding, you will need to set the instrument switch to 20 com. Next, insert one probe of the instrument into the cap of the spark plug, and connect the other to the “mass”. Normally, the resistance values should be in the range of 4-6 com and higher (depends on the model).

The tool will indicate infinity when the circuit is open, and zero (zero) when closed.

If you do not have a tester, you can use the following method, showing great care so that the electrode does not touch the cylinder, otherwise the coil will burn out.

  • Remove the spark plug cover. It is not necessary to unscrew the spark plug to keep the compression.
  • A nail without a cap should be inserted in the cap. The nail must be large enough to hold in the cap.
  • Attach the cap with the nail to the cylinder using dielectric so that the clearance between the electrode and the cylinder body is between 5.5 and 7 mm (but in no case touching the “mass”).
  • Repeatedly simulate engine starting with a starter motor. Ignition button must be on.
  • Observe whether the spark appears and what color it is.

Sparkle should be normal, strong, white or with a bluish tint. If the spark is faint and its color is orange or yellow, this indicates a faulty magneto.

Also consider the fact that sometimes a magneto in a cold state can give a good spark. But after heating up due to internal faults it stops producing current. As soon as the coil cools down, the grass trimmer starts up again and runs for a while until the magneto warms up again. Such a coil must be replaced.

Sometimes a similar problem with heating can be caused by the spark plug, even if the coil is serviceable, so you need to check both parts.

Algorithm for adjusting ignition

Ignition on the trimmer is fairly simple to adjust.

    Remove the shroud from the engine by unscrewing all the bolts holding it in place. For example, on Patriot (Patriot) PT 2540 petrol brushcutter, to remove the cover, you will need to unscrew the air filter housing, and a flat screwdriver to remove it from the latches. After that, the plastic housing is easy to remove.

Reasons for not being able to start the brushcutter

Here are the reasons why you can’t start your brushcutter engine:

  • In the fuel tank old exhausted gasoline;
  • The engine starting procedure is broken;
  • Short circuit of the wires going to the on/off button;
  • the ignition system is defective;
  • clogged air filter;
  • fuel filter is clogged
  • The fuel hoses are leaking;
  • defective breather valve;
  • The primer is broken;
  • The carburetor is clogged with dirt or malfunctioning;
  • the air damper actuator is broken;
  • the engine is defective (stuck rings).

There is old and exhausted gasoline in the fuel tank

Despite the fact that the instruction manual of each model recommends not only not to leave fuel in the tank, but also to preserve the engine, some owners of such equipment neglect these recommendations.

If the lid is tightly closed and the breather valve is intact, then petrol evaporates minimally during storage, but any leakage affects the fuel quality.

Because the volatile hydrocarbons evaporate and the remaining liquid absorbs water from the air. As a result, the combustibility of gasoline in the tank is insufficient to ignite the spark plug, so you can not start the engine.

To fix the situation, you must not only drain the old fuel from the tank, but also remove it from the carburetor.

This can be done in two ways:

  • Remove the carburetor, disassemble it and drain the remaining gasoline;
  • pump new fuel with primer, and then, pulling the starter rope dozens of times, pump the old gasoline through the combustion chamber until the new fuel appears there, then dry the spark plug.

The first method is more complicated technically, because not everyone can properly disassemble and assemble, and set in place the carburetor, and then connect it.

The second method requires high stamina and patience, because you have to pull the cord for more than one minute, while each time choosing a free move, because if you do not do this, you can damage the starter mechanism.

The engine starting procedure is disturbed

The operating instructions of each model of grass trimmer describes the procedure for starting the engine, both after winter storage or purchase, and during operation.

In addition, you will find universal starting instructions in this article. Violation of the recommended procedure often results in the owner of a brushcutter not being able to start his machine.

In this case we recommend to:

  • Read the user manual or the appropriate article;
  • Dry the spark plug (it is often flooded with gasoline or fuel mixture during improper starting);
  • Start your trimmer normally.
See also  Replacing Fishing Line In Trimmer: 2 Simple Ways

Short-circuited wires

To turn off the engine, the switch connects the wires that go to it and shunts (short-circuits) the ignition system on the low voltage.

Under the influence of vibration and because of the use of wires with poor quality insulation, the latter sometimes rubs together, which can lead to a short circuit.

Such short circuit performs the same function as the grass trimmer switch turned to the “off” position, so manipulation of the switch does not produce any result.

To diagnose damage, remove the trigger wire from the ignition system terminal (on some models, you will have to cut or unsolder), then use a tester to measure the resistance in the “on” and “off” modes between this wire and the motor housing.

If the button and wiring are serviceable, the resistance will tend to infinity in “on” mode and will show a short circuit in “off” mode.

If the wiring is damaged, then:

  • Disassemble the operating handle;
  • Desolder or cut the wires going to the button as well as the ignition system and engine;
  • pull out the old wires and insert new ones in their place;
  • tamper with or connect new wires with terminals;
  • Reassemble the crank.

The ignition system is defective

Here are the basic ignition system faults:

Incorrect gap between magneto and ignition coil

Two magnets inserted into aluminum flywheel of engine. When the motor is running, the flywheel rotates and the magnets pass by the ignition coil, forming pulses of electromotive force (EMF) in it, with two magnets providing twice the energy charge as one.

This energy is stored in a capacitor inside the ignition unit and after the passage of the second magnet, the stored energy in the form of a single pulse goes to the transformer, which is the ignition coil.

Effective impact of the magnets is only possible over a short distance, so the ignition unit is securely mounted, but the flywheel is set in a high temperature zone and its fins create an airflow that blows around the motor.

That’s why many brushcutter models have an adjustment of the flywheel clearance.

If the hood vents are clogged, the flywheel temperature becomes too high, leading to greater thermal expansion and the flywheel begins to cling to the ignition unit.

This results in much more vibration and causes the block to move away from the flywheel, which in turn leads to a larger clearance when the engine is cold.

The bigger the gap and the lower the speed of the coil’s passage through the magnetic field, the lower the EMF and therefore the lower the spark energy, which leads to a difficult or impossible cold start.

optimum clearance between coil core and flywheel magnets is 0.2 mm, about the same thickness of the wall of plastic sweet or mineral water bottles.

Therefore for diagnostics make the dipstick from such bottle, cutting it necessarily across, then the dipstick will curl and fit tightly around the flywheel or you can use the dipstick for adjustment of thermal gaps of valves.

Measure the thickness of the dipstick with a caliper or micrometer, and if the thickness matches, measure the gap with it, placing the magnets exactly opposite the block. If the dipstick enters with a force, the gap is optimal and you need to look for another reason, if it comes in easily, then loosen the fixing bolts, press the block firmly against the flywheel and fix it with standard bolts.

Be sure to clean the cowl vents and check their condition every day.

Faulty ignition coil assembly

If the gap is optimal, the wires are not closed, and the grass trimmer does not start, then check the unit for malfunction.

trimmer, spool

To do this, disconnect all wires from it, and remove the spark plug wire from the plug, then measure the resistance of both coils:

  • primary (between the motor housing and the on/off button lead), resistance 2-3 ohms;
  • secondary (between the engine housing and the spark plug wire tip) 4.5-5.5 kOhm.
trimmer, spool

If any resistance differs by more than 30% the ignition unit should be replaced. If there is no possibility or desire to measure the resistance, you can check the unit with an ignition tester such as this.

To check, remove the spark plug wire from the spark plug and insert the tip of the arrester into it and connect the arrester wire to the motor or any earth wire. Then set the gap at 0.5-0.8 mm and pull the starter rope, while looking at the spark.

If there is no spark, the lawnmower ignition unit needs to be replaced, but if there is a spark, the spark plug is most likely the cause of the problem and it requires.

Plug failure

If a spark plug failure is suspected, unscrew it from the cylinder head and inspect.

Contacts covered with black deposits indicate both the fault of the spark plug itself and the over-enriched fuel-air mix.

This can be caused by a dirty air filter or a malfunctioning carburetor.

To check the spark plug, you need to clean it in any convenient way, for example, soaking it in a solution of 9% vinegar for half an hour, then sprinkling with baking soda and after another half an hour rinse with water and dry with compressed air.

However, for a more reliable result, we recommend putting a new candle, if the trimmer for grass will not start to work normally, then the problem is not in the candle and you need to look for other problems, if the machine will work normally, then the preliminary diagnosis is confirmed.

After installing a new candle, we recommend checking it every 5-10 hours of work, if black sludge does not appear, then the old candle was faulty or of poor quality, if the new part will begin to turn black, the problem is in over-enriched fuel.

Clogged air filter

The main sign of a clogged air filter is the inability to start in normal mode, that is, with the transfer of the air valve in the closed position, but if you start the engine without closing the valve, it sometimes works. The engine may be difficult to rev up when running and its power output is insufficient to cut the grass.

Often because of a clogged filter black plug, to check its condition, remove the filter element from the body of the trimmer for grass (the way depends on the design of the device) and examine it.

If it is clean, it is not the problem, but if it is dark, then clean it according to the instruction manual of your brushcutter.

The fuel filter is clogged

The main sign of a clogged fuel filter is heavy starting of the engine, after which it immediately throttles. This is due to the fact that the filter capacity is lower than the fuel consumption of the engine, even at idle speed.

See also  How to Wear Stihl Trimmer Properly

To check, pull filter out of tank either through the filler port (a wire hook is required) or through the hole for the gasoline line and return hose that carries excess fuel into the tank.

If there is dirt on the filter, replace it separately or in the assembly with hoses and sealing rubber, parts or kits for such repairs can be bought both in parts stores and in Yandex Market.

The fuel hoses are leaking

The symptoms of this malfunction are very similar to those described in the previous section.

However, even for a short time to start the engine is much more difficult, in addition, during the attempt to start the power unit there is often a strong smell of gasoline.

To diagnose, remove the tubes from the primer and pull them out of the fuel tank, then evaluate the force with which they were able to be removed from the primer, as well as the overall condition.

If they have become stiff or easily removed from the primer, then change either the tubes themselves, making sure that the filter is fully functional, or the entire set, including the fuel filter.

Some brushcutter models have clamps installed, so before removing the hoses, carefully cut them, and after replacing the hoses, do not forget to install new clamps.

Remember, if there is a smell of gasoline, then the hoses need to change regardless of their appearance and condition, and if this does not help, then you will have to disassemble the carburetor and look for fuel leakage through the gasket or a loose part.

The breather valve is defective

The breather valve is a valve in the fuel tank, whose task is to equalize the pressure at the flow of fuel and prevent the outflow of gasoline when tilting the trimmer for grass.

The most frequent symptom of a clogged breather. the engine starts up, but in a few seconds it glows, because the consumed fuel is not compensated by the inflow of air, so the rarefaction in the carburetor and the tank is compared and the movement of gasoline is broken. We described checking and cleaning or replacing the breather plug here (lawnmower stops).

Broken primer

The main sign of malfunction of this part is a very heavy starting “in the cold“, because you have to pull the cord more than a dozen times, but if you stop the warmed up engine and within a minute to start it again, then a couple of jerks will be enough.

It happens because the primer valve does not prevent the return flow of fuel, so you can not pump it normally, but pulling the starter rope, you create a vacuum in the carburetor, which gradually draws fuel from the tank.

To replace the valve, you must remove and disassemble the carburetor, then change the rubber seal on the valve. If you do not know how to do it or are not sure that you can do it right, take your trimmer for grass to the workshop, you can also order the appropriate seals for your carburetor model.

The carburetor is clogged with dirt or has a defective carburetor

With such a malfunction, it is difficult to start the motor both “cold” and “hot”, and if you manage to start the machine after all, then it works poorly, that is:

If you have excluded all other faults, then either disassemble the carburetor yourself (we recommend not doing it without experience), or take it to the workshop.

Remember, the carburetor can not clog for one filling, this process even when using bad gasoline takes more than one hour, so do not wait until the machine will stop starting, and at the first signs carry out repairs.

Air damper actuator is defective

The main sign of such a malfunction is difficult starting a cold brushcutter motor, especially in low outdoor temperatures.

The warmed up engine will start with a pull or two of the recoil starter rope.

Sometimes the engine starts with ease “in cold conditions” but does not react on return of choke lever into operating position.

This is because the choke shutoff during startup (blow-by-suction) is no longer properly engaged in the lever and cannot be moved after it.

To check the air damper, disassemble the air filter and by moving the lever in different modes, observe the behavior of the damper. You can also keep the lever in one position and rock the choke gently with your fingers.

Even a small backlash indicates that both parts need to be replaced. You do not have to disassemble the carburetor, just remove the air filter housing, then replace the lever and slide.

You can buy them in most stores that sell spare parts for such equipment, or order them through the store on the website of the brushcutter manufacturer.

Engine does not run (rings are stuck)

This defect is rare and occurs only on trimmers that were filled with low-quality gasoline.

The main signs of a dead ring are:

  • Lawn mower does not start when it is cold;
  • Unstable idle speed;
  • Stabilization of engine operation after warming up;
  • Increased fuel consumption.

Since you need to disassemble the engine to confirm and fix the problem, rule out any other possible causes, and only then proceed to disassemble the engine. To repair a two-stroke motor it is enough to remove the head together with the cylinder, then knock out the piston pin and remove the piston itself.

However, to repair four-stroke engines, you will have to remove the timing chain and then almost completely disassemble the engine.

If you are not sure you can do the job properly, take your brushcutter to a workshop.

Remember, if the rings are not crumbled but sunk, you can repair them with a gas torch, it is enough to heat the piston near the rings so that all the oily deposits burn out. When this happens, the rings will click softly and detach from the piston.

After that, wait for the piston to cool and, after carefully removing the rings, use a paper knife to clean the channels, then put the removed parts back in place and reassemble the motor.

Lawn mower, grass trimmer valve adjustment

Unfortunately, the instruction manual gasoline grass trimmer Khoper Farmer VS-350 4T does not mention the need to check the gap and how to adjust the valves.

In fact, checking the valve gaps after 10 hours of operation of a new engine and then every 50 hours of operation of the lawnmower.

The clearance between the rocker arm and the valve stem should be 0,08-0,15 mm. This applies to both intake and exhaust valves.

We will use a 0.1 mm feeler gauge to check the clearances and adjust the valves.