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  1. #1
    Buck3yeRideR's Avatar
    Join Date
    Jun 2011
    Brunswick/Marblehead, OH

    Compression relating to ring gap & piston-wall clearance

    Just got my bored cylinders back from the shop and am almost ready to install and get out on the water!
    I wanted to get everyone's input on this and how these numbers relate to compression.

    For my ski (1995 sl650std) the following ranges are:

    piston-to-wall clearance .005-.007"
    ring gap .008-.016"

    One such as myself would think .005 and .008 would be the best scenario because of the tighter clearances. What's your thought?

    Recommended by xlint i got my pistons bored with .006 piston-to-wall, which i'm sure will work perfectly, however in theory for best numbers is the higher or lower range to any benefit?

    Next step is setting ring gap. Which value should I use? Any special tool recommended to measure?

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Gaps also depend on modifiactions to the engine. The more mods you have, generally the more HP you'll make. Therefore they tend to create more heat. So if you have more heat, you usually get more expansion of the metal, so you will want the gaps slightly larger to prevent possible seizure.

    Follow what I'm saying?

    So a bone stsock motor may be fine with the tightest tolerances possible, but a heavily modified engine may want something in the 10-12 thou range.

    Yes, usually the tighter the tolerances, the better the compression, but you're not going to gain all that much from a slightly tighter gap VS one a little bit bigger that's still within specs.

    Your skis are pretty much stock if I remember correctly. So anywhere from 8-10 would work fine I would think.

    You'll need a set of feeler gauges to check your clearances.

    And read the manual before you start doing anything. Then read it as you go to get a better understanding of what all needs to be done. This is not the time to make a mistake.

    PS: make sure your cyls are clean, I mean REALLY, really clean... Take a white rag through them, and if it comes out dirty, wash them again until clean.

    Then wipe them down IMMEDIATELY after with some 2 stroke oil or WD40 to prevent rust. It's amazing how fast those cast iron sleeves will rust.

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