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  1. #1

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    Compression swings after modded head installation

    98 GP1200. Sent my head out to Group K for milling. Before getting modded, compression was about 118 throughout. After mod, compression was about 140 throughout. Brought it out for 20 minutes of riding. Afterwards compression was down to about 123 throughout. 2 days later I checked compression with engine cold and it was up to130 throughout. Ran it on the hose for 10 minutes and rechecked. Compression was back down to about 123. Then I torqued down the head bolts no more than another 1/8 of a turn (my torque wrench doesn't go high enough to use so I guessed a litttle bit), ran it for a few more minutes, then rechecked compression. It was down to 120.

    Any ideas as to what the problem could be?

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  2. #2

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    Your head could have warped from improper torquing or your head gasket blew.

    You only need to torque the head bolts at 11 ft-lbs and then 23 ft-lbs. Are you using an inch-pound torque wrench?

    Test the compression wet by dumping a cap full of oil into the cylinder before you test each cylinder.

    I would take the head off and check for warpage, this is shown in the service manual, do you have one of those?

  3. #3

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    I have both N-m and in-lbs on my wrench, but I was going with the metric scale cause the engraved specs on the head are in N-m's. I torqued the head down properly, at least I feel I did. I torqued down in the correct pattern to about 2/3 spec, then went around again to full spec.

    Question, though...there are different specs for the head bolts and the head cover bolts. When following the pattern, do I torque down bolt 1 for the head then bolt 1 for the head cover (and so on to the end), or do I bolt down the head completely and then do the head cover (or vice versa)?

    If I remove the head after this little of run time, do I still need to get another new gasket?

    I do have a service manual.

    I appreciate the help.

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  4. #4

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    I can't remember the exact specs off the top of my head, but somewhere around 29.6 N-m for the head cover bolts, and around 34.3 N-m for the head bolts, which is a little more than the 23 ft-lbs you suggested.

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  5. #5

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    I always keep the cover attached to the head. No need to remove it, thats just another gasket you'll need. I would torque the cover down to spec in sequence 1 and 2, then bolt the head to the cylinders and torque it down to spec in sequence 1 and 2. I am pretty sure my head says the same thing but I always go by the book. If you use the metal gasket you should be good reuse the gasket...It is user preference though, some on here will say to not reuse gaskets.

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  6. #6

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    I wish I could've kept the cover on but Group K wanted me to take it off. In that diagram what do the 4 and 3 mean in "1 - 4: 4" and "5 - 14: 3"?

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  7. #7

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    Not sure what that means. I initially thought it meant 2 or 3 cylinders. but that doesnt make any sense. Do you need a service manual. Send me your email and I can send you one.

  8. #8

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    Is the head gasket wasted if i release tension and try to start from scratch again?

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  9. #9

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    The 3 and 4 refer to the step in the removal or installation. For example, bolts 1 through 4 are supposed to be torqued down to spec in 2-step sequence, then bolts 5-14, when installing the head (vice-versa for removal). I certainly didn't do that. I went 1-14 two-step sequence. And the head cover should be installed first before installing the head. I also wasn't aware that the M6 head cover bolts required much less torque than the M8's. Don't do what I did and snap a bolt. At least it's only the head cover and not the head. I'm going to remove everything and check for warpage and order a new gasket. I wish I went through my service manual a little more in depth than I did. I thought I knew exactly what I was doing. Lesson learned.

  10. #10

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    Anyone have a new head gasket for sale?

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