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  1. #1

    2002 GP1200R Compression and Break in Questions

    Yes, I did search but I didn't exactly what I was looking for.

    I just finished a rebuild of my 2002 GP1200R. The crank let go at 150 hours. I replaced the crank, the seals, the middle jug and piston and put in new rings all the way around. All cylinders looked excellent and still had all the factory cross hatch marks on them.

    My question is this, I used assembly lube on all the moving parts, especially the cylinder walls. I was meticulous in ensuring every thing was clean, lubed and torqued to the right specs. When I was done, the motor cranked right up and idled perfectly. I must admit I was somewhat proud. I've rebuilt 4 strokes, but never a two stroke. Any way, I checked the compression and it's as follows

    Cylinder 1 - 100 PSI
    Cylinder 2 - 105 PSI
    Cylinder 3 - 100 PSI

    I know this motor from the factory should be around 120 across the board, maybe a little less on #3.

    I'm using a high quality gauge, with all plugs out, on a cold motor with WOT. Can I expect this to get better after the rings have been seated?


  2. #2
    Mike xsockguyx's Avatar
    Join Date
    Sep 2007
    Once you take it out and the rings seat the compression should come up. New motors just read low.

  3. #3
    Join Date
    Oct 2006
    only remove 1 plug at a time...... also it will register a bit low until it is run and broken in as the rings are not yet seated.

    further to this you should comp test it when its warm, not cold.

    do a search on breakin methods as the way we do it around here is not the way yamaha says you should but our method works better.

  4. #4
    So are the numbers I came up with (100,105,100) normal for a fresh build?

  5. #5

    Join Date
    Jun 2008
    St Clair Shores, MI
    I hope so. I just put a (used) motor in mine with a fresh #2 cylinder and supposedly 10 hours on the others. With oil poured in the cylinders it read 150 150 150. With no oil it was something like 140 120 135. I'm hoping it comes up a bit more after the rings seat in.

  6. #6
    Well, for whatever the reason, I'm worried about it. What kind of improvement can I see after the rings get seated? Five, ten or fifteen PSI? I need to know so I can sleep at

  7. #7
    WATER WOODY's Avatar
    Join Date
    Aug 2005
    Minden, Nevada, United States
    what guage you using?

  8. #8
    I've used two different ones. One Snap-On and one made by Actron. Both read the same.

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