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  1. #1
    Gpr man now 9t8gp1200's Avatar
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    Help with cyl. bore questions

    I am rebuilding my GPR which broke the crank and scuffed up the #3 cylinder wall. They don't seem to be deep scratches and not too bad. What can I do to fix the jug I have? Do I have to go up in bore size to fix it or can it be re-sleeved? All help is appreciated!
    Thanks!
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  2. #2
    Old Ski Insanity w/rpm500's Avatar
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    good thing is, most are below the ports so no real loss in compression.. i would ball hone that very lightly.. this will take out the high spots the gouges have created and get new 'stock bore' rings .. run it oil rich for a tank or two ..then ride till you can afford to bore and go larger...my 2 cents..

  3. #3
    Moderator OsideBill's Avatar
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    GPR cylinders do not take too well to honing, the plating is not very thick. Millenium technologies repairs and replates cylinders for around $200 or you can find a good used one for about the same price, sometimes less if you are lucky.

  4. #4
    Old Ski Insanity w/rpm500's Avatar
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    this is your best bet then .. I'VE only worked with the unplated varity so I bow to OSbills advice,, once you get that one done back to o/e you can just freshen it all back to o/e(1 new piston, 3 ring sets, gaskets).. give millenium a call and see what a bore and replate cost for all three vs. the repair of one(3 bigger bore pistons, 3 rings, gaskets)..

    its pretty much pay to play now or now, then again, when you have the need/want to go bigger...

  5. #5
    WATER WOODY's Avatar
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    The cylinders can be honed and if the scratches are too deep and/or above exhaust port, then they will need stripping and replated. Honing is good for helping new rings set and taking out light scratches,basicaly a bore cleanup.We are talking a very light hone,nothing more.

  6. #6
    Moderator OsideBill's Avatar
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    can you feel the riges at all with your finger nails? is replate. If not sometimes you can get away with cleaning them with scotchbrite and a new piston set.

  7. #7
    Gpr man now 9t8gp1200's Avatar
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    I'm not sure that they are real deep...deep enough to feel with a fingernail. I will have to check it out tonight. I know you can feel it being kinda wavy rubbing a finger across it. I would love to go ahead and bore all 3 out to 1300...but I want to be riding by July, so funds might make me just fix this cylinder for now, then I can ride all summer and stock pile for a winter BB...1390 is what I really want.

  8. #8
    Old Ski Insanity w/rpm500's Avatar
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    WOODY CAN HELP YOU WITH THE FUTURE BB SENARIO!!


    IMHO,wavy with your finger and not just a nail catch means it was gouged or seized enough to have displaced metal (coating) ,leaving you high and low spots that are not just worn away like a scratch would tend to be..a hone/scotch-brite may knock those highs off enough to make this acceptable for the summer..only once assembled and given a comp.test will it tell your the results of this fix for sure(more than a 10% loss under the other two is not good). cheapest and quickest ..find a good used cylinder and piston..my 2 cents again

  9. #9
    Gpr man now 9t8gp1200's Avatar
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    RPM, I'm definitely gonna try to find a used one from under $300 and go that route for the summer. Then this winter I will have to go BB I'm sure!...BajaEater has a cylinder and piston he wants to sell, but I have not got a reply from him yet...we'll see where that goes. Thanks to all for the help on this!

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