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  1. #1

    What causes a MAG piston seizure on a domestic?

    On the "new" genesis, I ended up melting the MAG piston on the second day I took it out. Upon tearing it apart I found that only the MAG had already been bored .5 over and the other two were still stock. So obviously this isn't the first time this thing has lost the MAG piston.

    It wasn't a "lava" meltdown on the top, but a seizure/melt withing the bore. The rings were still intact and in good shape, but the side of the piston had melted to the cylinder wall.

    What should I look for? Obviously I'm going to check the carbs and clean/rebuild if needed, but looking at the wash I don't think it was a fuel problem - the wash was damn near perfect. Were there any cooling problems or updates with the '99 Genesiseseses? (Genesi? )
    Last edited by K447; 03-14-2011 at 08:24 PM.

  2. #2

    Join Date
    Jun 2010
    sutter, ca.
    sounds like a cooling prob. or when they put the over sized piston in it wasnt @ the right cyl. boar

  3. #3
    Quote Originally Posted by 3-banger View Post
    sounds like a cooling prob. or when they put the over sized piston in it wasnt @ the right cyl. boar

    Wrong bore is a possibility, but the fact that this is at least the 2nd time that it has killed the MAG, it makes me think it's more than that. Cooling is a possibility, but I'm not aware of anything that could be changed to help cooling only on the front cylinder - I haven't found any reference to a Polaris TSB on the subject.

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    Measure the piston to cylinder clearance as best you can, to determine if the piston was too tight in the bore?

    Can you tell what brand piston it was?

  5. #5
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ
    You have a case leak, would be my best guess. It's more than likely at a 3-point contact where the top/bottom halves meet and where the front case bolts on. Very common. Another would be the front case seal. It always seems to get the front jug on this engine.

    -crank timing.
    -carb issue.
    -fuel pump issue.
    -too big a prop, loading engine.
    -in rare instances, cooling water.

  6. #6
    thester71's Avatar
    Join Date
    Jun 2009
    central ma.
    It might be the exhaust manifold distorting the cylinder bore when you torque the bolts, did you torque the manifold to the cylinders before you torque the cylinders down?

  7. #7
    Rasta Mon Condoms We Be Jammin!!!!! TxPro1200's Avatar
    Join Date
    Aug 2006
    good answers but i'm thinking hydro's right if the mag carb screen isn't clogged.i made a tool to check water hose adapter,couple clamps,1" id tubing.with the water bar off the head covers,the pump removed,the stinger hose clamped off,the tool is clamped to the inlet water tube and you can see the water flow as it flows out each head cover

  8. #8

    I'm leaning toward air leak as well. Guess I need to do a leak-down when I finally get a new jug.

    Sucks...this thing doesn't have the same exhaust as my other domestics, I can't use my block-off plate. I guess I can pick up a spare manifold and bolt it on for the leak-down and use my plate.

  9. #9
    AWA Member 32DegH2O's Avatar
    Join Date
    Aug 2006
    Minneapolis, Mn.
    I would place my money on a leaking front crank to crankcase seal.

  10. #10
    bowsniper's Avatar
    Join Date
    Aug 2008
    were the rings stuck in the lands? did it have a 4 corner seziure? what does the piston look like? there are many reasons why they seize. is there scratches on 1 side only? or both opposite of each other? are there any acratches near the end gap of the rings?

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