All gasoline two-stroke engines have a similar principle of operation, and therefore the ignition system in them has a typical structure and device.
Chainsaw ignition device:
- Magneto: a device that converts mechanical energy into electrical energy and provides a current pulse to the chainsaw’s spark plug;
- Spark plug: designed to ignite the fuel-air mixture, through the discharge occurring between the electrodes;
Spark plugs come in spark, arc, glow, and catalytic. Spark plugs for 2-stroke engines are used in chainsaw devices. The chain saw ignition diagram is shown here.
STIHL MS 180 C-BE chainsaw: Mounting the bar and chain, tensioning the saw chain
Chainsaw ignition diagram
STIHL chain saw 180 reciprocating piston group description
On the STIHL chain saw 180, the piston group has a diameter of 38 mm. Chainsaw spark plug size is determined by the diameter of the piston, the cylinder is slightly larger. The MS 180 CPG is fitted as standard with a piston pin, two piston rings and two clips.
The distinctive feature of the CPG on the STIHL MS 180 is that it has two compression rings, whereas almost all its main competitors only have one. According to the manufacturer, installing a pair of rings helps to better stabilize the piston during operation, increase its cooling and increase compression in the engine, thereby improving startup.
If the machine won’t start, the first thing to check is the spark plug, which is what ignites the fuel in the cylinder. Start by removing the spark plug wire. Unscrew the spark plug itself from the cylinder head and check its condition. The spark plug should be dry when working properly and there should be small deposits on the ceramics of a light color:
- If the spark plug is wet, there is a problem with the carburetor. Need to adjust and set the fuel level in it;
- Dark or black carbon deposits on spark plug walls indicate a problem with the piston group.
If you find no apparent cause of the fault here, the spark plug is dry, the soot is light continue to go from the reverse. Since this is the final point of ignition of the mixture. Now check to see if the spark is coming to the spark plug. This is the ignition unit.
The main thing in this group of problems is the engine.
The ignition is one of the basic elements affecting the trouble-free operation of the tool. So the first thing we’ll consider is this unit.
Gone are the days when ignition control was handled by a breaker with cams and a moving contact that provided the spark to the spark plug.
It was not a very reliable system because of the many elements that affected the operation of the engine. A chainsaw with no visible faults might just stop starting. And we could see the picture of constant yanking on the ignition cord. Today, manufacturers have moved to a contactless ignition system.
How to choose a spark plug for a chainsaw
Despite the uniformity and interchangeability within the respective parameters of the spark plugs even of different brands, this is a very important point.
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Most importantly, the length of the filament (skirt) is exactly the same as the original spark plug.
- If you screw in a spark plug with a long thread, it may reach the piston and be damaged even if you try to start the engine. The candle will reduce the gap.
- If the threads are too short, the fuel mixture will ignite in the cylinder thread channel instead of in the combustion chamber. The chainsaw may even work for a while, but soon this channel will be completely covered with soot.
The instruction manual for each chainsaw specifies exactly which spark plug is used. According to this you should choose a new one.
If the manual is lost or the chainsaw is bought off-hand, choose a candle that informs the seller of the chainsaw model. But there is a risk of finding a poorly matched counterpart.
Third option. Choose the size, marking and appearance of the native candle.
Even if the spark plug works fine, it is advisable to have a spare. This is for diagnostic purposes. If a chainsaw stops, the first thing they do is replace the spark plug to see if it has a cause.
This is necessary in order not to stop the chainsaw if one spark plug fails unexpectedly and at the most inopportune moment.
A chainsaw consists of many components that are important to the machine’s operation, including the spark plug. This small part needs to be replaced periodically. You can replace it yourself. Usually it is sufficient to use universal instructions, which fit all models of the power unit. But before you look for instructions, you’ll have to buy a new part. Not sure which spark plug to choose for your chainsaw? This and other information is available in this article.
An average is considered to be no less than 0.2 and no more than 0.4 mm. If the correct gap is not maintained, the base ignition system will not be able to generate the spark required to ignite the fuel mixture instantly and on time.
- remove the cap from the spark plug and put a nail in it. Be careful not to damage the inside of the cap
- Position a nail 6-7mm from the cylinder.
- “Start” the engine, i.e. do the usual steps for starting the tool
- Look for the spark and color
- Important points:
Algorithm of removal and installation
In cases where the STIHL 180 carburetor needs to be cleaned or disassembled, you will first need to remove the assembly from the chainsaw. This should be done according to a certain algorithm:
- Put the chainsaw cover on the guide bar.
- Remove chainsaw top cover.
- Unscrew two nuts fixing the air filter and carburetor.
- Remove the air filter housing.
- Disconnect the wire from the engine control lever.
- Carefully remove the lever from its seat in the housing, while disconnecting the air damper rod from it.
- Pull the carburetor toward you and disconnect the fuel supply as well as the throttle linkage.
Algorithm of troubleshooting
In all other cases, the search for ignition faults starts from the end and in order. After each step, check the spark.
- Replace old candle with guaranteed working one.
- If the model has a removable spark plug cover, it is removed and the exposed spark plug wire is shorted to ground with a gap similar to that of a spark plug. Pull starter. If the spark is there, the problem is in the cap. It’s eliminated.
- Replace the spark plug wire where it is possible to remove it from the source.
- Visually inspect the wires from the switch. In case of vibration, in case of contact with metal, they can be damaged. Если места трения есть, провод меняют, даже если нет внешних повреждений изоляции. Use a tester or multimeter to check the wire.
This is the end of small and easily fixable problems. If the problem is not solved, then the cause is more serious. Modern coils and ignition systems on most chainsaws are very reliable. They are designed for an even longer service life than the chainsaw as a whole. They have no mechanical moving parts like the old cam systems. They are sufficiently isolated from clogging and moisture.
If by an accidental factory defect there is an intercircuit in the coil or the electronics fail, these parts cannot be repaired. Would need to be replaced with new ones.
There is a mechanical failure, which is not uncommon. Because of wear or destruction of the crankshaft bearing, there is play on the crankshaft. And then the magnetic rotor gets caught in the ignition system housing where it rotates. This is a serious breakdown. It is necessary to disassemble the whole motor, replace bearings and reassemble everything.
In all other cases, the search for ignition faults begins at the end and in order. Check the spark after each stroke.
- Replace the old spark plug with a guaranteed working.
- If the model has a removable spark plug cover, it’s removed and the exposed spark plug wire is shorted to ground with a gap similar to that of a spark plug. Pulling the starter. If there is a spark, the problem is in the cap. It is eliminated.
- Replace the spark plug wire wherever it can be removed from the source.
- Visually inspect the wires from the switch. If there is vibration, in case of contact with metal, they can be damaged. If there are places of friction, the wire is replaced, even if there is no external damage to the insulation. You can use a tester or multimeter to check the wire.
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This is where minor and easily fixable problems end. If the problem is not solved, then the cause is more serious. Modern coils and ignition systems on most chainsaws are very reliable. They are designed to last even longer than the entire chainsaw as a whole. They have no mechanical moving parts like the old cam systems. They are fairly insulated from clogging and moisture.
If by an accidental factory defect an intercircuit in the coil happens or the electronics break down, these parts cannot be repaired. You need to replace it with new ones.
There is a mechanical breakdown that is not uncommon. If the crankshaft bearing is worn or fractured, it is allowed to have play. And then the magnetic rotor starts to get caught up in the ignition system housing, inside of which it rotates. This is a serious damage. You would need to “hollow out” (disassemble) the entire motor, replace the bearing, and put everything back together.