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  1. #1

    01 genesis 1200 piston size question

    Working on my '01 genesis 1200 i and it had about 90 lbs of compression in the rear cylinder so i decided to go to the dealer and order a new piston...went and picked it up today and have been working on it but i noticed that the old piston said 84.00 or 84.08 on the piston and my new piston is oem (same piston) and it says 83.83 on the piston head but on the piston box it says 84mm..I installed the piston and you can jiggle it a little bit and there seems to be a little bit of play between the cylinder wall and the'll work for awhile but i dont know for how long? Should i return this piston to the dealer and get a new one or will I be ok??

  2. #2

    Join Date
    Jun 2008
    Sudbury, Ontario
    Get a vernier caliper and measure the diameter of both pistons, 83.83 should be stock....did you order a stock piston...

  3. #3
    I did order a standard bore oem piston..i will try and get it measured tomorrow but I just don't get why the new one says 83.83mm and 84mm on the box but the old piston said 84.00 or 84.08mm??? With this smaller piston will I lose compression??

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    Clearance between the piston and the cylinder is critical. Too little and the piston can seize in the bore while the engine is running.

    Too much clearance will allow the piston to slap inside the cylinder, which will break the piston.

    Was there something wrong with your old piston?

  5. #5
    The old piston had some scoring on the sides of it and I didn't really want to use it...compression in the cylinder it came out of was only 90lbs as well so that was another factor..i did install the piston in the cylinder and the ski runs good..but the compression readings are kind of weird...the mag cyl reads about 135-140lbs...the center cyl reads about 130lbs and the pto (which is the new piston) reads about 120lbs.

  6. #6

    Join Date
    Aug 2010
    corona, ca
    I dont think I would be ok with that much variance..your new piston should be highest in PSI.....

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