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Thread: compression difference

  1. #1
    Member AKMarmot's Avatar
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    Default compression difference

    I have a 70hp 4 stroke that shows compression in # 3 & 4 to be lower than #1 & 2. If a the acceptable range is 15 psi #3 doesn't make the cut.
    ( 1 & 2 are running @ 190, # 3 is 167 & #4 is @ 176 )
    Can I take it out & run it & see if there is a sticking ring or noticeable problems or do I need to have it taken to the shop & torn apart?

  2. #2
    Moderator Paul H's Avatar
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    Default

    Did you warm it up before checking the compression? If not, warm it up for awhile and recheck. Even if you did warm it up, it doesn't hurt to run the comp check a second time.

    If the comp numbers hold true, I'd say you will want to do something about it. With two cylinders about 10% below the other two, something is going south. Could be a burned valve, not necessarily a ring problem.

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