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  1. #1

    GPR engine building question...please help

    Ok, so I haven't had my ski out for two years now. Anyway, last year I rebuilt the engine after seizing a piston the year before. I replaced the cylinder and piston with used parts, but used new rings on all three. When I put the new rings in the used pistons, some of the rings were getting stuck in the ring lands. Meaning that when I compressed them to fit in the cylinder bore, they got pinched in the piston and would not open back up. I figured that the heat would loosen things up when it was started. The crank appeared to be ok and was turning freedly. I didn't see any heat discoloration. So, I put everything back together and it fired right up and revved up nicely. However, when it came back down to idle, I would get an intermittent banging noise. It definitely sounded like metal to metal contact. I did check the compression after rebuilding and it was roughly 110 psi across the board. Obviously, the rings didn't have enough time to seat fully. So feeling frustrated, it sat until this year.

    I just took everything apart again and didn't notice any obvious metal to metal contact areas. I expected to see damage to the cases or crank, but nothing. At least one of the rings was still compressed when I took it apart. I'm wondering if anyone has had a similar experience using new rings in a used piston. Also, will a new piston allow the rings to move freely? And do you think the rings caused the piston to slap and make the noise?

    I already have a new crank and plan on buying a new top end. I don't want to take a chance and miss another season. Or do all this work just to be frustrated again. Thanks for you help.


  2. #2
    Yamaha artisan Cutlass's Avatar
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    You could probably sand the rings down on a piece of glass or granite to achieve the proper clearance.
    Here's a thread of mine describing it a similar issue:
    http://www.greenhulk.net/forums/show...arance.-GP1200

  3. #3
    Thanks for the reply. L Carlson was able to help me out. Apparently, the rings are beveled and you can install the rings upside down even though they're not marked. By flipping them it seems that they are moving much more freely in the ring lands.

  4. #4
    L Carlson's Avatar
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    Quote Originally Posted by Cutlass View Post
    You could probably sand the rings down on a piece of glass or granite to achieve the proper clearance.
    Here's a thread of mine describing it a similar issue:
    http://www.greenhulk.net/forums/show...arance.-GP1200
    way bad idea as far as im concerned! Would never in a million years do this to a motor I would build for myself!!!

  5. #5
    It looks like the rings have a teflon coating on them. By sanding them you'd be removing that coating.

  6. #6
    Yamaha artisan Cutlass's Avatar
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    yeah in that case, sanding them would be a bad idea. I'm not sure if my rings were like that or not, but I didn't end up sanding mine. Sanding would be a last resort, if money was tight or no other solution worked

  7. #7
    Yamaha artisan Cutlass's Avatar
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    Quote Originally Posted by L Carlson View Post
    way bad idea as far as im concerned! Would never in a million years do this to a motor I would build for myself!!!
    yeah I didn't feel right about doing it either, so I didn't do that to mine.

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