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  1. #1
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    Merc V6 running compression #s Wats good?

    I've got a 2.4 that's running at 145psi all 6 with engine running at 1,100 rpm is that about right it has 120psi cranking all 6 just checking thanks Keaten

  2. #2
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    I've got a 1988 2.4 175 hp. that shows 130-135 cranking compression on my gauge.

  3. #3
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    I wanna say keaton 2.4 had 130 psi cold cranking, 120 warm

    I've never checked comp running on a outboard, so really wouldnt no what to expect. Sure it will b higher tho

    Not to change subject but if mota has 145 -150 wonder what's its pumpin out runnin?
    Last edited by Merc 2.5; 09-12-2019 at 05:43 AM.

  4. #4
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    Might be a silly question guys, but how do you check compression while engine is running? Are you just running it on 5 cylinders with the gauge in the 6th?

  5. #5
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    Quote Originally Posted by stream18 View Post
    Might be a silly question guys, but how do you check compression while engine is running? Are you just running it on 5 cylinders with the gauge in the 6th?
    I guess that's only way to check that I know of

  6. #6
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    Yes I have nothing against cranking speed PSI checking. It just seems more natural and meaningful to test the cylinder and ring health this way. I only run it for about 10 Sec per cylinder @ 1,000 rpm. After proper warm up on water hose. Works great for me. Thanks Keaten

  7. #7
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    Quote Originally Posted by Merc 2.5 View Post
    I guess that's only way to check that I know of
    Yes that's correct

  8. #8
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    In every type of engine you should check compression when the engine is at operating temperature.

    Engine doesn't have to be running. Get it hot, pull the plugs and go cylinder to cylinder. Turn the engine over 5 or 6 seconds. This will send the pistons up and down several times.

    I have 2 gauges that read the same. I do 2 cylinders at a time.
    .

    I've bought and sold 22 boats in 26 years. I fix them up and then get bored and look for another. It's a hobby.

    Now running a Liberator 21 with a 300xs


    .

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  10. #9
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    Not gonna tell u anything on a 2 stroke engine... the best compression test is to only let it pump 3 or 4 times and do them all the same, no extra pulses for the lazy ones... Cranking on a cylinder until it finally makes it doesn't count to me and running would pretty much do that. That said this is a cylinder/piston condition test so yes you may crank it over 8 or10 times and get a little more if your looking to see what your peak compression # is for tuning . A compression test is to look for a given loss that's going to be amplified and rob hp when the cyl pressure is 10x the cranking at max rpm # faking it will only slow u down.. jmho.. Dave
    Last edited by H2OPERF; 09-13-2019 at 09:46 AM.

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