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Harrison256

Compression

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Harrison256

Should I be concerned if one cylinder on my boat is 20 pts lower in compression than the rest of my cylinders?

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Bake's Marine

Nope, not at all. You just don't want it to be 30% less than the highest number.

If you ran your engine first and ran it to temp i bet that variance would go away too. If you do it when it's cold you can get some really weird readings because there is not any oil on the rings.

-Paul

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martinarcher

Nope, not at all. You just don't want it to be 30% less than the highest number.

If you ran your engine first and ran it to temp i bet that variance would go away too. If you do it when it's cold you can get some really weird readings because there is not any oil on the rings.

-Paul

Plus1.gif Couldn't agree more.

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Woodski

I would do a leak down test if I found one cylinder down in compression to the rest. I would first probably redo my compression test to make sure it was accurate. The leak down test will pinpoint where the 20 points might be going, but as noted, it too must be done after the engine is at operating temperature and there is a film of oil on the rings or it will give erroneous readings.

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Pistol Pete

I'm not a mechanic but, you're also supposed to have all the plugs out and holding the throttle wide open while cranking. Don't forget to disengage the fuel and ignition system while doing this.

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JUST-IN-TIME

all 4 stroke motors you want do to a leakdown test

compression test are so-so

leakdown pin-points it

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Harrison256

someone was trying to tell me that means i have a blown cylinder head.. hope hes wrong

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footnlongline

someone was trying to tell me that means i have a blown cylinder head.. hope hes wrong

I wouldn't worry to much about that. Head gasket, maybe but I doubt that too. Compression checks can sometimes give you false readings, kinda like those blood-pressure monitors at the drug store, one day your fine and the next your 485 over 250. After running it on the water, does the plug on the opposing cylinder look similar?

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