Ask the Mechanic

Steve Thompson, Contributing Columnist

READER: I have a smaller Stihl chain saw that has been a great tool around our ranch for years. I read in one of your articles many years ago where you recommended never loaning a chain saw or hay baler to a friend. You recommended getting them out of a bind by going to their place and cutting their wood or baling their hay. I didn't listen, and my cousin asked to borrow my saw.

When it came home, it looked OK, so I put it in the shop. When I grabbed it the other day to cut a limb off the fence, it would not start. After extensive "Bubba" diagnostics, I found that it had only 60 pounds of compression. That is all it would get after cranking it over several times with the compression gauge in the spark plug hole.

I know it is a little engine, but how much compression should it have? Oh, by the way, I did not furnish him the fuel mix when he got the chain saw.

STEVE: I bet he put straight gas in your chain saw and ruined the engine. This is a common problem. If you must loan your chain saw, be sure and furnish the user the fuel to use. Your engine, even though small, still must have high enough compression to fire the fuel/air mixture. Most saws like yours will pump up to around 140 pounds. If you remove the muffler, I bet you will see scratches on the side of the piston. Suggestion: When Santa brings you a new chain saw, don't lend it out.

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-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email mechanic@progressivefarmer.com, and be sure to include your phone number.

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