Yamaha GP800 66e Cylinders
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  1. #1
    PWCToday Newbie
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    Yamaha GP800 66e Cylinders

    if my cylinders have little scratch marks on the bore can I just bore it up bigger buy .25 and just buy a piston with plus .25 size??


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  2. #2
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    Re: Yamaha GP800 66e Cylinders

    I donít think so, they have that nikasil coating on the walls not a steel sleeve like most motors. I donít know how thick that coating is though. It might hold up to just .25 over but Iím not 100% sure.


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  3. #3
    Frequent Poster Dave in DE's Avatar
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    Re: Yamaha GP800 66e Cylinders

    If they are still the original cyl and an unmelested motor they are nikasil coated and non bore able. They can be either replated or bored and sleeved. If they are nikasil and barely damaged I would replate them. Contact USChrome. I think cost is about $300. but to sleeve it would be about the same. If the motor has been rebuilt once already then it could be a sleeved cyl. Clean the head gasket serface well and look for the sleeve parting line of dissimilar metal. Steel/aluminum. Sleeve is about 1/8 inch thick.
    Nikasil is a hard chrome coating that reduces friction in the cyl and transfers heat faster through cyl wall to water faster than a steal sleeve. I believe USChrome has some cyl available for exchange witch makes for fast turnaround time.

  4. #4
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    Re: Yamaha GP800 66e Cylinders

    Quote Originally Posted by Dave in DE View Post
    If they are still the original cyl and an unmelested motor they are nikasil coated and non bore able. They can be either replated or bored and sleeved. If they are nikasil and barely damaged I would replate them. Contact USChrome. I think cost is about $300. but to sleeve it would be about the same. If the motor has been rebuilt once already then it could be a sleeved cyl. Clean the head gasket serface well and look for the sleeve parting line of dissimilar metal. Steel/aluminum. Sleeve is about 1/8 inch thick.
    Nikasil is a hard chrome coating that reduces friction in the cyl and transfers heat faster through cyl wall to water faster than a steal sleeve. I believe USChrome has some cyl available for exchange witch makes for fast turnaround time.
    thanks for the info. now i will send it to uschrome

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  5. #5
    Resident Guru JC-SuperJet's Avatar
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    Re: Yamaha GP800 66e Cylinders

    Friend had a Polaris Pro 785 with Nicasil Cylinders, just like the Yamaha Nicasil Cylinders. If the Nicasil coating was undamaged, he would simply clean the cylinders with Muriatic Acid and then install new stock size Pistons and Rings.

    If the Nicasil Coating is damaged, then it would need to be replated/relined/recoated.

    So the question is, at what point do they need to be replated? Check the Yamaha Service Manual for parameters. Call US Chrome for more info. But don't be to fast too replate if not necessary.

    If they have Sleeves, then they would need to be Bored and Honed to the next size up, as the per other comments above.
    Last edited by JC-SuperJet; 09-29-2018 at 11:56 PM.

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