# How to test chainsaw compression?



## hcrew (May 7, 2010)

I guess you remove the plug, insert the rubber end of the tester and pull the cord. Any finepoints: How fast to pull the cord; engine hot or cold, etc.?

For a Husky 266, what's a 'good' range for compression?


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## stevohut (May 7, 2010)

*testing comp*

There's a little more to it, don't worry I'll walk you through it. Take the plug out. Clean the matting surface of where the plug seats to the head. Check the o-ring on the head of your comp tester, make sure its not cracked. Put a little oil on the o-ring for lube. Screw the tester in the head ( hand tight only) Now open your throtle wide open to get a complete volume charge in your cylinder. Pull the starter rope vigorously about 3 times. (Make sure the ignition is turned off while pulling the engine over. If you leave the ignition on and your ignition high tension lead is not grounded you can damage the ignition coil) Now stop pulling and check your number on the guage. Repeat this process about 3 times and average the numbers you get on the guage.
Now pull the spark plug out and add to the combustion chamber a couple drops of oil. Slowly turn the engine over a couple times to dispers the oil around the rings. Put your guage back in and pull over vigorously about 3-5 times. Check your numbers on the gauge and take an average. If the difference in the numbers between the wet test versus the dry test you know you have a leak in your engine. Ideally you want less then a 10% difference any more is not good. Most likely you could have a stuck ring or if its a removable head a buggered head gasket or o-ring. You could also have some scoring in your cylinder deep enough to bypass the rings. A better test to perform is a leak down test it's more accurate for finding leaks throughout the whole engine. Hope this helps

steve


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## hcrew (May 7, 2010)

*testing comp*

Steve, thank you so much for the detailed instructions. Some of it comes back to me when as a kid over 60 years ago I bought a Model A for $50 and worked on it a full year ... experience is the best teacher and I greatly appreciate you sharing yours with me.
Henry


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