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  1. #1

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    high compression head question

    I put on a riva cut oem head for 150 psi . i did a compresion check after i rode it i have 145 front cyl 155 middle 165 rear is this to much variation ? should i pull the head check to see if something happened to that front cylinder ? When i rode the ski ran great it hesitated once The ski is an 01 gpr carbs have been jetted and i do have t handles is also premix .
    Last edited by harleyboy61; 08-29-2009 at 06:35 PM.


  2. #2
    I would do a double check on the compression again before opening the motor. Verify torque also.

    Battery must be full, power valves closed, throtle opened

    If it still has a 10 psi difference, open to check for score marks

  3. #3

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    any one else have an opinion before i pull the head again ?

  4. #4
    WATER WOODY's Avatar
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    Harley, you running gas valves? Either way, make sure your pv's are all down,mechanical/gas. Make sure your linkage (couplers) have no slack.

  5. #5

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    [quote=WATER WOODY;1189946]Harley, you running gas valves? Either way, make sure your pv's are all down,mechanical/gas. Make sure your linkage (couplers) have no slack.[/quot

    Running mechanical valves i will check linkages and recheck compression before i pull the head . If i get the same results should i pull the head and see if i have any scoring , or just run it and see if i lose more compression.

  6. #6
    If you have the same results, don't run it until you check the cylinder walls and pistons/rings to prevent further damage. You can post pictures also, many experts here will know what caused the damage (if any) and advice you what to check.

  7. #7

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    Quote Originally Posted by chris1200 View Post
    If you have the same results, don't run it until you check the cylinder walls and pistons/rings to prevent further damage. You can post pictures also, many experts here will know what caused the damage (if any) and advice you what to check.

    well i did what you said and checked it again still all over the place on the readings .So i popped the head the cylinder closeest to the front of the ski had some scoring but nothing i can even catch a finger nail on middle had a little also . But i did notice some sludge on the head compared to the other 2 cylinders . So i did some searching on the hulk seems like may have ingested some water either through the intake or the head not sealing . So i cleaned everything up reinstalled the head ran it retorqued the head and did another comp check . front 148 mid 155 rear 160 . Which is much better and even than before . This is an sbt motor with sleeved cylinders besides few scoring marks i did notice that there is some clearance between cyl wall and piston but not sure how much is normal .

  8. #8
    I would remove the cylinder to check for out of roundness and check ring, piston and cylinder clearance.

    All specs are in the GPR manual which is posted in this forum.

    Also measure cylinder height, could be cut lower than the other two and not allow proper seal.

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