No compression #4 cyl.

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Posted by Steve Kaminsky on October 20, 2003 at 12:32:53:

In Reply to: No compression #4 cyl. posted by David Keelan on 20:40:22 10/18/03:


It sounds as if the exhaust valve on the #4 cylinder is stuck open.

The following is a warning note from Don Moyer's website

"IMPORTANT NOTE: During most troubleshooting work, it is frequently necessary to turn the engine over on the starter with the engine NOT STARTING. Be sure to close the raw water thru-hull valve during these times so as to avoid filling the exhaust system with raw water until it backs up into the exhaust manifold, and into the combustion chambers of the engine."

You may want to try a Marvel Mystery Oil treatment before removing the head.

A Mystery Oil treatment is nothing more than putting 5 or 6 squirts (from a "squirt" type oil can) into the spark plug hole, and running the engine until the smoking stops. You can do this 3 or 4 times, and then check compression again.

You can also try to free up the stuck valve (through the spark plug hole) by using a long, thin screw driver in which you have put a bend in the end so that you can use it to pry the stuck valves closed. However, before a would do that, I would shoot 3 or 4 sqirts of Marvel Mystery Oil into each of the cylinders and let it soak in for a while. Or if you feel more ambitious, you could remove the valve cover plate, located on the carburetor side of the engine and try freeing up the valves from that location.

I hope this helps,
Steve Kaminsky

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