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  1. #1

    Smile 99' gp800. Cylinder wall is slightly damaged. I want to bore for bigger pistons.

    I just bought a 99' gp800 with the knowledge that a ring might be damaged and thats why the compression is low.
    I bought it for a great price and decided to work on it. After I opened it up I found the rings were broken and also that the piston scratched the upper part of the cylinder wall. (note: only one cylinder wall was scratched...I was told it happened because of people beating on it with high revs while in the air)
    I would rather bore it out to put bigger pistons in rather than getting all new cylinders. However, I cant find any info about Big Bore Piston Kits for that model or how large of a bore I can make.
    Can anyone help with some info..anything and everything is wanted
    thanks


  2. #2
    jdog800's Avatar
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    This is a powervalve motor and the cylinders are nikasil coated so if they are bored they have to be sent out and recoated. Your powervalves will also have to be resized for the new bore. If you bore one you have to bore the other one so there is the expense of doing both.
    ProX has the pistons you will need just get what ever bore you plan on going to.
    You could just have the one bad cylinder resleaved and put another stock piston back in it. This will probably be the cheapest route. Jfyi

  3. #3
    Old Ski Insanity w/rpm500's Avatar
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    post a picture of the damage!! ..an additional band-aid move,till you bore larger..if the scratch is level or below the upper part of the exhaust port openings, you may be able to run this with new rings ,with out much apreciable power loss..if it is above the open porting ,where your compressing the 'contained' mixture,you will get a power loss..
    if so,follow the course jdogg has noted above..

  4. #4
    thanks a lot for the info guys. I took a ton of pics but for some reason it wouldn't allow me to post them. I think its because I just joined.. I knew about the special plating that it had but I did want to bring it to the machinest tomorrow to see if it has ripped through the plating completely. It's pretty significant though :s but I was hoping to turn it into lemonade. I'm not sure how thick the plating is because I believe I only need like no more than 2 mm of bore. Well, I'm gonna take it tomorrow and see if it is past the point of no return..if it is then I'm definitely gonna just sleeve it.. I think it was caused from the kid over revving it while in the air everytime..beatin the piss out of it. What do you think? just curious...thanks a lot for the advice

  5. #5
    Old Ski Insanity w/rpm500's Avatar
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    imt,the plating is no where near that thickness.. (remember 1mm =.040 inch)

    .there are few companys that strip and replate nicasil..run a search for them here..to nicasil a cylinder is not resleeving ,its a plating on the sleeve that needs to be applyed once the sleeve is replaced or bored...( i may be wrong on this .. someone chime in if i am..)

    if you want larger you must do both cyl's... figure the costs for going larger vs. repairing what you have.. larger as a kit may not be that far from buying idividual pieces..piston, rings, gaskets, powervalve machineing.. then figure too, the cylinder mismatch of fresh vs. worn stocker...might not be much but at say 6000 rpm it will show..

  6. #6
    jdog800's Avatar
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    The nikasil coating is put on after the cylinder has been bored. If you can catch your fingernail in the groove of the scratch, It needs to be bored or replaced. If you replace the cylinder it also must have the nikasil coating on it if it doesnt already have it when you buy them.

    saw this sleeve on ebay
    http://cgi.ebay.com/ebaymotors/NEW-Y...rcraftQ5fParts

    so you should be able to come out pretty cheap this route.

  7. #7
    jdog800's Avatar
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    jftwc
    The reason that the power valve motors use the nikasil coating is to help control cylinder heat expansion and allows for tighter tolerances, and less heat build from friction. This control of heat expansion by the nikasil coating is essential to keeping the cylinder area around the powervalve from expanding too much and causing valve failure. This also allows the manufactures to use light weight aluminium in there pistons and sleeves rather than cast iron which is heavier.

  8. #8
    Thanks a lot guys. I'm taking the cylinder up to a local machinest and he said I can sleeve it and bore the sleeve out. He also said that he has a gp1200 in there with the same problem..ugh. The quote was around $400 for labor and a new piston with rings and pin and of course the sleeve. I guess the cylinders weren't getting enough oil and thats why it happened also that the kid who had it before must of been beatin on it..redlining like crazy. I dont want to spend the money only to let it happen again. He said as long as I maintain it then it will last a long time. Any suggestions as far as maintnance..best oil to use..check the oil and fuel lines and pumps? thanks fellas
    This is the first jetski I bought but I'm learning quickly

  9. #9
    I just found this guy on Ebay who can nikasil my cylinder for me with a top end rebuilt kit for around $500.. Doesn't seem like a bad idea.
    http://cgi.ebay.com/ebaymotors/Yamah...rcraftQ5fParts

  10. #10
    Old Ski Insanity w/rpm500's Avatar
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    jdog800.. do you know this guy? jet ski haven? he's out of la. too..
    I think that SAID 1 cylinder.. is that 500 for both or one!?

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