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The mechanic gave me a compession test reading of 123 and 125 on the #1 and #2 cylinders as well as 12 and 11 % on the leak down test.

Since I don't know what the compression readings were when the engine was new and have never heard of a leak down test until I was advised to get it done at the last minute, I'm a bit at sea on how to read the data. The mechanic (Mercury certified) told me the engne was fine.

I have already gotten one answer from "wannabe" that says readings of 10% and under on the leak down test are considered good readings and the 12 and 11% readings are marginally good - whatever marginally good means.

Does anyone else have knowledge about this data and how I should read it - then what I need to do, if anything? Celt

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A leak down or "cylinder leakage" test is similar to a compression test in that it tells you how well your engine's cylinders are sealing. But instead of measuring pressure, it measures pressure loss. An engine in great condition should generally show only 5 to 10% leakage. An engine that's still in pretty good condition may show up to 20% leakage. But more than 30% leakage indicates trouble. The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going.

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Thanks CES.

Therefor I should proceed as if the engine is on the high end of "pretty good" and nothing needs to be done with it at present other than maintain it by the book and run it in a prudent manner. The mechanic resealed the lower end and refilled it with lube oil. He also replaced the aluminum trim tab and thermostat. He said it needed nothing else.

Again my thanks for your prompt reply.

Celt

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The other benefit of the leakdown test, which a more thorough mechanic will take advantage of, is the ability to move the piston down in the cylinder, lock the flywheel, and perform the test at that position. This will check for integrity in the cylinder wall as well as an out of round condition.

Celt, If you're concerned about the leakdown results, ask the mechanic if he can remove the exhaust cover and take a look at the condition of the piston rings and skirt through the exhaust port. If the rings aren't carboned up from cheap oil or the like and all floating freely, and the skirt doesn't show signs of scuffing, it's a very good sign.

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If you're only getting 10-12% leak down, I'd call it good and run her until she drops.

Dave makes some great points as well. If, however, the motor seems to be running well...why fix what ain't broke?

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Thanks guys....I'll keep her running and maintain her until she dies, hopefully of old age in the distant future.

Celt