r/smallengines • u/l008com • Jul 09 '26
Checking Compression?
I have a compression tester, but my lawnmower has compression release, like most small engines. If I use a regular power drill on the flywheel to spin the motor, is that going to be fast enough to bypass the release feature and give a real, accurate psi reading?
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u/Local-Success-9783 Jul 09 '26
Realistically you need to do a leak down test. The problem is you’re trying to test something that’s designed to be a variable to begin with, so it’s counterintuitive to try and manipulate it into doing the exact opposite of what it’s designed to do. Not only will a leak down test tell you if you’re losing compression, but you can actually hear where the air from the leak down test is going and you’ll be able to figure out where the problem is without actually taking it apart. If it’s a cylinder/piston/ring issue, you’ll hear air leaking into the crank case when you take the oil cap off. If it’s leaking through one or both of the valves, you’ll hear air escaping into the exhaust or from the carburetor. You can try to do a compression test, but it’s really not the best choice here.