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  1. #1
    AquaGuy's Avatar
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    What should GP1200r compression be?

    Hi,

    I just got my GPR back from a top end end rebuild. I went for a ride today and it ran great. I checked the compression and it was:

    Rear cyl:113

    Middle cyl: 113

    Front cyl: 106

    These numbers seem low for a fresh top end especially the 106 don't you think? I thought this motor is supposed to put out 120 psi?

    I tried looking for an answer in the stickies and could not find it.

    I also have a second question. I noticed alot of water sits around the spark plug base where they meet the head. Is there anyway to prevent the water from gathering there?


  2. #2

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    thats a bit low make sure your tester is good with a fresh o-ring.... should be about 125-130 or so from what i have read and always gone off of.... however my xlt is around the 115 mark on all three and runs great!

  3. #3
    AquaGuy's Avatar
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    I am pretty sure my tester is good but will replace the o ring and try again. I am really bummed about this. I paid good money for this rebuild. I have a theory about what have happened. Tell me what you guys think: The mechanic who did my rebuild uses a pretty hard break-in process. He actually redlines the motor for quick bursts. I always use the soft break in method. I'm thinking maybe the high rpms caused the rings to not seat properly? Just a thought.

  4. #4
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    over time as they wear the top end, compression drops slowly.....about 120-125psi is about correct for a stock 1200r motor.

    the cylinders should all be within 1-3psi of each other.....

    the EFI models like the 06 were about 130 or 135 ( i forget) psi stock.....but they are a much newer ski and a 1300cc not a 1200.


    something is not right with your rebuild, i would get that resolved before riding it again as its not worth risking it.

    are you sure they rebuilt it, where are the old parts from the top end? i bet they didnt give them back to you because they reused them.

  5. #5
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    Quote Originally Posted by AquaGuy View Post
    Hi,

    I just got my GPR back from a top end end rebuild. I went for a ride today and it ran great. I checked the compression and it was:

    Rear cyl:113

    Middle cyl: 113

    Front cyl: 106

    These numbers seem low for a fresh top end especially the 106 don't you think? I thought this motor is supposed to put out 120 psi?

    I tried looking for an answer in the stickies and could not find it.

    I also have a second question. I noticed alot of water sits around the spark plug base where they meet the head. Is there anyway to prevent the water from gathering there?
    When you checked the compression did you have all the spark plugs out, On the 2 strokes just take out the plug that you are checking the compression on and the other 2 cylinders just remove the wires and ground them, Also make sure to hold the throttle wide open. With them numbers i would not worry after a full break in they tend to go up about 7 to 10 psi.

  6. #6
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    Quote Originally Posted by AquaGuy View Post
    I have a theory about what have happened. Tell me what you guys think: The mechanic who did my rebuild uses a pretty hard break-in process. He actually redlines the motor for quick bursts. I always use the soft break in method. I'm thinking maybe the high rpms caused the rings to not seat properly? Just a thought.
    Actually the high rpm burst and then letting up helps the rings seat quicker any good tech will tell you that you do not want to baby a new motor the best way to break it in is wide open bursts for a couple seconds and let off and let it coast down do about 4 to 5 of them, After that shutting it down so it can cool down for about 10 minutes. And doing it over again.

  7. #7
    AquaGuy's Avatar
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    Quote Originally Posted by JIM'S PERFORMANCE View Post
    Actually the high rpm burst and then letting up helps the rings seat quicker any good tech will tell you that you do not want to baby a new motor the best way to break it in is wide open bursts for a couple seconds and let off and let it coast down do about 4 to 5 of them, After that shutting it down so it can cool down for about 10 minutes. And doing it over again.

    Ok that is good to know. Yes I rode it shut it off to let it cool and rode again. I will ride it some more burn up a full tank of fuel and see where the compression stands then. Yes I had the plugs in the other cylinders I wasn't testing and WOT.

  8. #8
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    I'm with Jim on this one. The tech's break in procedure is typical. You need to load up the rings forcing them outward against the cylinder wall so they seat properly. When you baby an engine on break in the cylinder walls glaze over preventing the rings from seating as well as they could. A few high load bursts with breaks in between and cool down time is good.

    I would definitely go back to that tech though and ask a lot of questions and ask for all of your old parts.

    Those compression numbers should go up with a little more break in though. My '00 gp1200r is at around 99hrs and compression is 116-117 across the board, you really don't want any more than a 10% difference between cylinders but it shouldn't be anywhere near 10% difference following a fresh rebuild.

  9. #9
    GoFastGuru's Avatar
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    where are you at compression is higher at sea level .dont like the differance though.proubly not seated that ring set yet

  10. #10
    AquaGuy's Avatar
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    Well I pretty much finished the break in. I got a fresh o ring for my tester and the numbers now are:

    Rear 114

    Middle 114

    Front 112

    Still seems rather low for a fresh top end no?

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