Yamaha leak test

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  1. #1
    PWCToday Newbie
    Join Date
    Sep 2021

    Yamaha leak test

    Is it better to test an engine for air leaks using pressure or vacuum? Vacuum is more real life as an engine runs, but pressure would show up better using soapy water to snoop for leaks and is easier to do with equipment I have. Anyone here have any experience using one vs the other? Would it matter?

  2. #2
    PWCToday.com Is My Home Away From Home wmazz's Avatar
    Join Date
    Jul 2013
    Riverside, CA
    Blog Entries

    Re: Yamaha leak test

    Kawasaki always recommended a pressure/vacuum test.

    The problem with only a pressure test is the main seals. The main seal
    has two functions: seal pressure, and seal vacuum. The problem
    is that the pressure side of the main seal is well lubricated, and will
    hold pressure even if the vacuum side is completely worn out.

    It is common to find grease, and metal bits in the front main bearing
    if the vacuum side of the main seal is worn out.

    If you try a pressure vacuum test, remove the front mag cover to
    expose the front main seal, or possibly just remove the starter motor.
    On Kawasaki's it is an easy test, you just remove the inspection plug
    on the front cover.

    7psi/7 in-hg. for 5 min. is all that is necessary because that is the
    average pressure and vacuum for a crankcase.

    Bill M.

    If you have an engine failure, don't bank on the idea that just a
    pressure or vacuum leak will cause a seizure. Normally there is more
    than one problem that causes a failure.
    Horsepower == Speed, RPM != Speed

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