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  1. #1

    Mixing OEM sized pistons with oversized pistons

    I am helping a friend with a '96 SLX. It holed a piston and another one should probably be replaced. It currently has original-sized pistons. My question is: what happens if I mix original sized pistons with oversized pistons, say .75 over? Is this just begging for problems or should it run ok if I end up doing this?

  2. #2
    The last time we took this topic everyone seemed to agree that it's not a good idea do to the displacement difference!

  3. #3
    mxl16's Avatar
    Join Date
    May 2005
    Central NJ
    i have no experience with polaris but just from general engine balancing knowledge each piston and rod assembly for each cylinder should be weight matched (precisely). if not it will create a "slight" imbalance. how slight it is would depend on how big the weight difference is.

  4. #4
    Your changing from 744 to about 760 in that one cylinder! also like posted above Weight
    How bad is the cylinder? maybe just a quick hone? Z

  5. #5
    Banned User
    Join Date
    Aug 2006
    A 0.25mm difference won't hurt, but anything bigger will.

    From a builders standpoint (and I'm not much of one) the pistons should be around 10 grams of each other for a good balance.

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    If 1 maybe 2 are bad, why not replace all 3? Seems silly to try and save a few bucks on 1 cyl. Just get the piston kit and do all 3 the proper way. I'd hate to see you posting how you should've done them all during riding season.

  7. #7
    Water Bum Rodneyae's Avatar
    Join Date
    Dec 2006
    Roanoke, Va
    I would do all three.

  8. #8
    I'm asking this question because the person that owns it has already bought the ski twice over in repairs...After taking the engine apart I've figured to fix it the way I would they need $600+ in parts.

    It sounds like they don't really want to spend that kind of money & probably just want to sell it. SOooo...I have a .75 cylinder & piston sitting here that I was thinking I could maybe put on for them. Put it back together for them rather cheap(we're talking under $100 here probably) so they could atleast ride it a few more times before it dies again & they sell it. Then again..if I can get it's troubles made right maybe it would go as-is for a while!

    So, I don't think I'll do this. Maybe I'll see if I can find a decent used original sized piston instead.

  9. #9
    make them spring for the minimum oversize piston! it's only 70.00
    a bore is 35 and honestly I reuse gaskets all the time! condition Dependant of course! Z

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Boring is cheap by you Z. I was quoted $70 a hole for .010 OS up here.

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