Cylinder wear?
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Thread: Cylinder wear?

  1. #1
    PWCToday Regular
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    Cylinder wear?

    How's my cylinder look to you guys? The pistons look fresh but the cylinder doesn't look that great to me. I don't have a bore gauge but would placing a piston ring at different spots down the cylinder and measuring ring gaps give me a close enough idea of how out of round the cylinder is?

    Also a few of my crank needle bearings have a slight amount of pitting/corrosion....They should be flawless right?

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    IMG_20181104_034102965.jpg

  2. #2
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: Cylinder wear?

    Without a bore gauge it's just guesswork, take it to a machine shop and let them measure it for you
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries


  3. #3
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    Re: Cylinder wear?

    You're right WFO. Definitely need precision measurements. I got 0.001" out of round, 0.001" taper, and + 0.0035" bore.

    Also pulled my crank out and it's in bad shape as well. Seems like I have the 1986-87 engine since the crank doesn't have the locating ring on the middle bearing. Can I just remove the ring on the 88+ cranks??

    IMG_20181110_071234660.jpg

    20-203B-V1.jpg
    Last edited by johnlam940; 11-10-2018 at 02:22 PM.

  4. #4
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: Cylinder wear?

    Yes there are actually three different crankshafts as explained in the K-tech news article copied and pasted below :

    Which
    crankshaft?

    The first JF- and JS650 crankshafts were located in the cases by a dowel pin in the center seal. Since then the design has been changed twice. If you are ordering either a crankshaft or crankcases for a 650 JET SKI watercraft, be very careful to order the correct one by engine number. If you are ordering both cases and crankshaft, it’s probably best to order the latest part numbers. Once again, select the part numbers off the microfiche carefully. For your information, the first design (with the dowel pin in the center seal) is superseded by a second design which has a half-circle retaining ring in the front center main bearing. Both crankcase and crankshaft retain the dowel pin hole for compatibility with the earlier parts.

    The third design has a thinner, full-circle retaining ring in the front center main bearing. This is not compatible or interchangeable
    with either of the earlier designs unless the crankshaft and cases are replaced as a set. - Gregg Thompson
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries


  5. #5
    PWCToday.com Is My Home Away From Home
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    Re: Cylinder wear?

    Use a baseball. Actual whiffle balls flex a lot.

    Make sure not to let the wallaby eat it, it'll get stuck in it's esophagus. That's no good.
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