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  1. #1

    New cylinder screech/scrape?? (97 Pro 785)

    This is long so I'll cut right to it.

    My manifold mating surface on my old cylinder chipped when an exhaust manifold bolt broke. This seems endemic (bolt break) to these Pros? Anyhow, this meant water sprayed all over between cyl. and mani. mating surface and serious performance loss...yadda yadda. With a chipped mani. surface coupled with a stuck broken off bolt I decided to spend $150 for new cylinder instead of trying to rehab this cylinder.

    Buy stock bore cylinder from Randy which is perfect and recently honed. I have no probs with his cylinder, it looked/looks good. Install it with same piston, rings, etc that I have not removed.

    With cylinder on, but head and valve off, crank over by hand.....perfectly smooth motion, no noises.

    With cyl. and valve on, head off, crank over by hand......ditto.

    Same scenario but crank over with starter: smooth and no noises.

    Head on, no sparkplugs, crank with starter: ditto w/ good compression blast.

    Finally.. head on, sparkplugs in, compression force on rings: crank over by hand...smooth no noises with good solid compression "ca-chunk".

    Same scenario with starter: Out emits a horrible screeching noises from center cylinder, the one I replaced.

    I tear it back apart. Find very minute, very seemingly inconsequential scrape marks on the lower half of what was a perfectly honed cylinder. They are below and around exhaust ports level....the top half of the cylinder is perfect...unscathed.

    I assume my rings are in wrong (off line) so I double check, reinstall and try again. Exact same results...worse screeching/scraping this time.

    I lubed the hell outta the thing before I even cranked it by hand. I know it is the center cylinder because of one-by-one sparkplug removal. It was not doing this before with the original center cylinder. Can my used piston just not fit this new cylinder somehow? They are both stock bore. Should I replace the piston, rings, etc on this cylinder and try again or is there something else to check before I do all this? Maybe just new rings? Should I do new pistons, rings, hone, etc on all three over the winter while I'm at it? This is a sub 70hr engine that had good comp. on all three before this ailment the whole shebang seems unnessecary because I know mag and pto are still good compression. I'd like to ride again before the season is over. (On lake Superior, so soon)

    The new cylinder is still good without a hone (I think) as I stopped immediately each time after this sound. I can post pics if that would help tomorrow. It only happens when I use the starter and the cylinder/piston is under compression with the head on and the sparkplug in so I assume it's a ring issue?

    Please help! Any advice is greatly apprreciated! Randy?

    Thanks in advance
    Last edited by WIslxer; 09-27-2007 at 03:01 PM.

  2. #2
    Join Date
    Jul 2007
    Cedar Rapids,Iowa
    I'd mic the bore and piston just to make sure the clearance is right.Also check ring gap. I'd also never run used rings after a bore or hone job.
    Last edited by Keddano; 09-27-2007 at 12:14 AM. Reason: thought

  3. #3
    Quote Originally Posted by Keddano View Post
    I'd also never run used rings after a bore or hone job.

    You're right I should have gotten new rings regardless. My guess is/was tired rings, or so I hope?

  4. #4

    Join Date
    Aug 2006
    Homer Glen Il.
    check the ring gap and are the factory polaris pistons or wiseco . also is are the sides of the pistons scrachted up at all

  5. #5
    PolarisNut's Avatar
    Join Date
    Dec 2006
    Lower Michigan
    Always, always, replace rings when the cylinder is renik'd and/or honed. I've seen lots of nikasil cylinders that are only a few hours old that have "scuff" marks in them from the rings. Not sure why its happening, but I've seen it.

  6. #6
    Hell Bent or Heaven Sent? Bent's Avatar
    Join Date
    Jul 2007
    Pinawa, Manitoba, Canada
    were the ports chamffered good?

  7. #7
    These are the stock factory rings. The piston had some minute scuff marks on it as well. Not sure about port chamfering. This is a Watcon cylinder so I assume it's good to go. So new rings are #1?

    Thanks. Keep the tips coming!

  8. #8
    Watcon's Avatar
    Join Date
    Oct 2005
    Seattle WA

    785 Blues

    Disassemble the motor, and check the "ring-end" gap. Check the cylinder to piston clearance also, but the ring end gap is most important.. Are you using Wiseco pistons??

    Are you sure the lower- end bearing is good? as that will make noise and introduce debris to the cylinder walls.. Take photos of the piston and cylinders..


  9. #9
    Thanks Randy. Will check clearances. This is stock piston, stock rings. The lower end bearing seems good, tight and smooth. Plus there was no probs regarding this before I switched cylinders. The one I took off was flawless internally. I will re-disassemble and return with photos. Randy I may call you looking for advice and rings. My name is Jonah. I bought this cylinder from you earlier in the mid-summer.

    Thanks again. Keep it coming.

  10. #10
    absentx's Avatar
    Join Date
    Aug 2006
    WIslxer...Your nuts man, whats Lake Superior this time of year...maybe sixty degrees??? Haha, I love the great lakes

    I am in Hayward this weekend, might take the pro out on a small local lake here.

    Anyways, check that ring end gap like Randy said, and if you need new rings, I have plenty that are brand new, just let me know.

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