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  1. #1
    SpeedDemon99's Avatar
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    VXR Compression 180psi? & plug pics

    I was winterizing my 12' VXR with 50 hours and did a compression test with all plugs out, cold engine, WOT and cranked up 5-6 times each reading before the needle stabilized. Here's the results:

    Cylinder #1: 180psi
    Cylinder #2: 170psi
    Cylinder #3: 170psi
    Cylinder #4: 180psi

    Seemed very high to me considering the service manual says 110psi is spec. I tried each cylinder a couple times and got the same results. I used my new craftsman compression gauge.

    Here is what the plugs look like (from left to right order is cylinder 4,3,2,1):



    I checked the gaps also. Yamaha says 0.031-0.035. By spinning the plugs till they stop on the gauge I was getting about .037 inches.

    Cylinder Plug#1:

    Cylinder Plug#2:

    Cylinder Plug#3:

    Cylinder Plug#4:


  2. #2
    big john's Avatar
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    try another compression gauge, that's not right, mine was 150 last time i checked and that was with +5/0 degrees on the cams, i haven't checked it since re-timing them to +7/-2

  3. #3
    Pain is fear leaving your body.... rlovebk's Avatar
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    The biggie is they are well within range (10% +/-) of eachother.

  4. #4
    SpeedDemon99's Avatar
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    I wish I had another gauge to try but my old cheap one crapped out which is why I bought this new craftsman set.

  5. #5
    AWA MEMBER
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    Those plugs look like a decent burn.........tad rich High 11's

  6. #6
    Vern's Avatar
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    180 does not seem off to me ... honestly the manual stating 110 as 'normal' seems very surprising. The SC'd Doos measure 135 - 160+ depending on cam timing, and only have 8.4:1 compression, so 180 on the much higher compression VXR NA motor is what I would expect to see. Cam timing can make a large difference on measured compression, so that may account for some differences ...

  7. #7
    Yellow93's Avatar
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    Try taking one plug out at a time and checking compression, thats how I've always done it. I bet the numbers are more in line.

  8. #8
    mjh3ides's Avatar
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    I wouldn't worry about the compression. The manual for the lower compression SHO motor shows 87psi as the spec, & if I remember right mine was 140-150 on my gauge. I'm pretty sure the number they give you is absolute pressure, so you need to add 14.7psi(1 atm at sea level). Obviously that still doesn't add up to what you're seeing so I'm not sure how sure how they come up with that spec.

  9. #9
    SpeedDemon99's Avatar
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    Thanks for the responses guys. I'm going to rent a compression gauge from Autozone to compare just for the hell of it. I know my engine is good from the differences in PSI but now I want to know if my gauge is accurate.

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