Six reasons for the chainsaw to fail

In many homes and farms the chainsaw is a seasonal tool, and it is expected to perform at the pull of a cord. Despite their seemingly simple design, there are many intricate components that rely on each other to get the best out of the saw, writes James Maloney

Chain won’t stop turning

The clutch pads engage the clutch drum to rotate the chain. When the engine slows, the return springs retract the pads to disengage the chain. If the springs are broken, the clutch pads won’t retract, preventing the chain from stopping. If the clutch pads are sticking, the clutch drum will stay engaged and continue to turn. If the springs are broken or the clutch pads are sticking, replace the clutch assembly.

Engine running rough and cutting out during work

A clogged carburetor is often caused by leaving fuel in the chainsaw for a long period of time. Over time, some of the ingredients in the fuel may evaporate, leaving behind a thicker, stickier substance.

This sticky fuel can clog up the carburetor and cause the chainsaw engine to stall. If the carburetor is clogged, try cleaning it with carburetor cleaner. If cleaning the carburetor isn’t effective, rebuild or replace the entire carburettor.

The spark arrestor is a small screen that prevents the engine from emitting sparks. Over time, the spark arrestor can become clogged with soot. If the spark arrestor is clogged, the chainsaw may stall or run rough. To unclog the spark arrestor, remove it and clean it with a wire brush. You can also replace the spark arrestor.

The air filter may be clogged or dirty. If the air filter is clogged, the engine will get too much fuel and not enough air. As a result, the engine may stall or run roughly. Inspect the air filter to determine if it is clogged. If the air filter is clogged, replace it or clean it.

Starting trouble

The spark plug might be defective. To determine if this is the case, remove the spark plug and inspect it. If the porcelain insulator is cracked, an electrode has been burned away or damaged, or there is heavy carbon buildup at the electrode, replace the spark plug. Alternatively, if the spark plug hasn’t been replaced in a few seasons, replace it as a general maintenance practice. The spark is created by getting the electrical current to jump or arc across the electrode gap at the top, if this gap is not clear or covered in oil the engine will fail, as the fuel and air mix will not ignite to create power. The ignition coil sends voltage to the spark plug while the engine is running. If the ignition coil is defective, the engine may not start. Before you replace the ignition coil, make sure the carburetor is not clogged, giving too much fuel and not enough air.

Loose chain

When the tension in a chainsaw blade is low the blade cuts less effectively and the functionality of the unit decreases.

This loosening most frequently results from a dull chain and can be remedied by having the teeth on your chain sharpened.

To tighten the chain once it has been sharpened or replaced, use a wrench to loosen the bolts on the side of the body of the saw situated near where the bar exits the engine housing.

On most saws there are two bolts. One holds the plastic covering that contains the gear that drives the chain and the other holds the bar in place on an adjustable track.

Engine oil and fuel mix

Chainsaws use two-stroke engines, so essentially in one stroke of the piston induction of the fuel and oil mix and compression occurs, while in the second stroke is the power stoke where the explosion or ignition and exhaust occurs.

Two-stroke engines have no oil sump or air-cooling system. The advantage of this is that they are much lighter and can be used at any angle. The fuel oil mix lubricates the moving parts inside. If you forget to add oil for one tank of petrol, you will destroy your engine.

Mixing too much oil with the petrol will cause the following problems:

Many engines and chainsaw suppliers will supply details on the correct mix ration of fuel and oil. Some mix bottles will have a very simple line measurement for petrol, and then a line for the oil mix. Typically, if there is a ratio of 25:1 for oil and fuel, that means 25 parts of petrol to one part of oil or 25 litres of petrol to one litre of oil.

For most of us 25 litres of fuel is way too much, so we can work it back by doing the following calculation. If you are using five litres of petrol, divide five by 25, which gives 0.2 litres of oil or 200ml to be added to a five litre can. Always check the ratio requirement. The big advantage is that there is never any need to change the oil.

The lighter two-stroke engine runs at a higher rpm when compared to the four-stroke engine, making it very suitable for the chainsaw.

Dealing with a flooded Engine

Engine flooding happens when petrol is in the compression chamber before it ignites. This stagnant petrol prevents the spark and ignition of the engine. It must be drained from the system before the engine will start. The best way to do this is through persistent, repeated attempts yanking the pull cord with the saw switched off. So essentially the pull cord is pushing the piston up and down, and hopefully emptying out the chamber of fuel. After eight to 10 attempts, turn on the saw, pull the choke out, and continue in this fashion until the engine turns over. After the first time the engine turns, push the choke in and pull until the saw coughs to life.

Preventing overheating

Cooling a two-stroke engine is easy, as it uses a simple fan and fins around the engine. The action of the air passing over these fins removes the heat. The fins located around the cylinder where all the heat is generated, create a bigger surface area to dissipate the heat away. When using a chainsaw outside during the summer it is easy to overheat your engine. To prevent this it is important to clean the inside of your saw routinely. The important thing when cleaning your chainsaw is to clear the air intake areas around the starter and the cylinder area especially. These places can frequently get clogged with sawdust and wood chips. Cleaning your chainsaw is a good way to get to know its assembly.