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  1. #1
    mikevv's Avatar
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    Problem Solved: What is a typical compression reading for a stock SHO?

    What kind of hot compression readings are people getting?

    Edit: Thanks to everyone that contributed their ideas and compression numbers. As it turned out the gauge was OK but the Schrader valve in the hose was either too stiff or gummed up a little. I put a new softer valve in and everything works fine. I have 125# in all four cylinders. At least one mechanic told me that the valve is different for smaller engines than large V8s. I may have had the right valve for a V8 but not an SHO.
    Last edited by mikevv; 05-30-2012 at 07:24 PM. Reason: problem solved


  2. #2

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    Yamaha service manuel "86.8 psi @ ambient tempature 68* F with sparkplugs removed from all cylinders". This seems low to me but this is what the manuel has printed in it .Tommy Jordan

  3. #3
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    Quote Originally Posted by mikevv View Post
    What kind of hot compression readings are people getting?
    about 120 on average with a stock motor.

  4. #4
    mikevv's Avatar
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    Quote Originally Posted by JIM'S PERFORMANCE View Post
    about 120 on average with a stock motor.
    That's more what I would expect. I did a baseline check on my 2008 SHO at 130hours last fall before I made a number of mods over the winter. The gauge I have read 65# cold last fall and about the same when I ran it this spring and checked it warm. Assuming my gauge is correct 65# seems pretty bad for 130hours?

  5. #5
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    Quote Originally Posted by mikevv View Post
    That's more what I would expect. I did a baseline check on my 2008 SHO at 130hours last fall before I made a number of mods over the winter. The gauge I have read 65# cold last fall and about the same when I ran it this spring and checked it warm. Assuming my gauge is correct 65# seems pretty bad for 130hours?
    65 is very low but if all 3 read that low i would try a different gauge, Sounds like a gauge may be bad.

  6. #6
    WATER WOODY's Avatar
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    Quote Originally Posted by JIM'S PERFORMANCE View Post
    about 120 on average with a stock motor.
    That seems correct because we are 22-25 psi down up here at 4500' elevation. My SHO with a Snap-On guage shows 93-96 psi up here.

  7. #7
    mikevv's Avatar
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    Quote Originally Posted by JIM'S PERFORMANCE View Post
    65 is very low but if all 3 read that low i would try a different gauge, Sounds like a gauge may be bad.
    I checked the gauge and it seems ok. Certainly not off 2 to 1. Is there any trick to checking compression on a supercharged motor? I hold the throttle open so it won't pump fuel and send a spark but with throttle by wire is the throttle plate really open?

  8. #8
    YAMAHA POWAAAA !!!!! 1_Fast_SHO's Avatar
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    Checked mine after a 180 hours and only # 2 was low at 90. Replaced piston ring set in all four after breake in all 4 were at 130. Like alway i agree with Jims 65 is very low even for 130 hours.

  9. #9

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    Why would piston ring go bad less than 200 hours? is this normal or is because your ski has lots of mods and it is being pushed?
    Quote Originally Posted by 1_Fast_SHO View Post
    Checked mine after a 180 hours and only # 2 was low at 90. Replaced piston ring set in all four after breake in all 4 were at 130. Like alway i agree with Jims 65 is very low even for 130 hours.

  10. #10
    YAMAHA POWAAAA !!!!! 1_Fast_SHO's Avatar
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    Quote Originally Posted by CaptainReza View Post
    Why would piston ring go bad less than 200 hours? is this normal or is because your ski has lots of mods and it is being pushed?
    it had a couple of mods including reflash and E1 but also the ski was pushed by running lean,

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