Chain Saw First Aid – The ABC’s

Spring 2014

Have you struggled getting your saw started after a long cold winter?

Have you pulled and pulled on a starter cord so many times that you just wanted to chuck the thing?

If you answered yes to one or both of these questions, then your saw needs first aid. This article is on the basics of starting a chain saw and how to make a hard starting saw an easy saw to start. Just like any first aid course, we start with the ABC’s - Airway, Breathing and Circulation.

It has been said that a chain saw is an air pump. The reason for this is because it moves air more than anything else and every cubic centimeter of air has to pass through the chain saw engine’s air filter. An average chain saw engine size is about 50 cc’s with engines ranging in size from as small as 30 cc’s to 100 cc’s and over. The ‘cc’ stands for cubic centimeters, which is the volume of the engine head and every time the piston goes up and down, it draws in and expels cc’s of mostly air. On the compression stroke or upstroke, air is mixed in the carburetor with some fuel and oil. On the exhaust or down stroke, it expels exhaust out of the muffler.

Chain saw engines run at approximately 12,000 RPM, which means the crankshaft does 12,000 revolutions per minute and for every revolution of the crankshaft the piston does an upstroke and down stroke and the saw draws in and expels air on each stroke. If we use a 50 cc saw as an example to calculate how much air passes through the air filter every minute, all we need to do is multiply 50 cc by 12,000 RPM; which would mean that 600,000 cubic centimeters of air would go through the air filter of a 50 cc saw engine every minute. The air and filter represent the ‘A’ and ‘B’ of the ABC’s of chain saw first aid. Be sure the airway is clear and unobstructed.

It is recommended to clean your air filter by simply removing it and washing in warm water with some dish soap (refer to image 1). It is important to keep the airway open and unobstructed. Your saw engine’s breathing will be good if the filter is clean. Give the filter time to dry before trying to start your saw, usually about 15 minutes in a warm dry place like a window sill is all it takes (refer to image 2).

In order to check and clean your air filter, you first have to take off the top and/or back cover of the saw and another fastener must release to get the air filter off (refer to image 3). It is a good idea to clean the area around the filter with a brush before removing the air filter to ensure no debris falls into the carburetor once the air filter is removed. On older model saws, the application of the choke will serve to block debris from falling into the carburetor.

Next is the ‘C’ of the ABC’s. Circulation for the chain saw means fuel. Chain saw engines like high octane and they do not perform well with methanol or ethanol. Fuels with these additives should not be used in chain saws. Ready to use fuel is now available for chain saws and is stabilized to allow for long term storage. This advanced high performance fuel does cost more, but is well worth the time saved in having a saw that starts easily and runs well. STIHL MotoMix^® is an example of this ready to use fuel and eliminates the hassle of mixing your own 2-stroke engine fuel.

Chain saws that have been in storage a long time struggle to start and run because the fuel in the tank and/or fuel jug becomes stale when left sitting for too long. Your saws running and starting ability will be reduced after about 3 months of fuel sitting still and this only gets worse as more time passes.

To help your saw start and run better simply empty the saws fuel tank and re-fill with a fuel from a freshly mixed jug (refer to image 4). Follow the manufactures mixing ratio recommendations which is typically a 50:1 ratio of fuel to oil. The small convenient little containers of mix oil are made for adding to the 5 litre fuel jugs, but be sure the fuel you purchase is premium grade 89 octane or higher. One final important point about fuels is that dyed or farm fuel is not good for chain saws, as the dye used to mark this fuel can react with the mix oil and result in engine damage.

Finally, top up the bar oil reservoir with bar and chain oil. This is the other cap on your saw and this oil reservoir needs to be filled every time the fuel tank is filled. The bar and chain oil don’t affect engine performance but they are required for overall saw performance. If you are finding the chain is stretching often and the bar is getting hot, then you are most likely running the saw with the bar and chain oil reservoir empty; and although the saw will run with this oil reservoir empty, it just won’t perform. The circulation of the chain around the bar is lubricated and facilitated by the bar oil. The ABC’s of chain saw first aid are; ‘A and B’ clean the air filter and ’C’ put fresh mixed fuel in the tank. 90% of the time when this is done, the saw will fire and run in just a few pulls.

Also, remember a cold saw needs to be choked. A cold saw is a chain saw that has not run in the past hour. Once the engine fires, even if it only fires briefly, turn the choke off before continuing to start. Otherwise, you will flood the engine and starting will be very difficult again, but now for other reasons.

So many times students and friends have brought me their saws because they can’t get them to start or run, and the first thing I do is the ABC’s and ‘Voilà!’, the saw comes to life!

by Dwayne Neustaeter
Arboriculture Canada Training and Education Ltd. www.arborcanada.com