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  1. #1

    wsm piston clearance for 650

    hi…my brother is getting in a wsm .25 over piton kit for 650….what should we tell the engine guy to do with it?

    last piston kit we bought was pro x….it had no instructions with it for clearance….so any input on the wsm clearance….plus should we tell him to chamfer the port…top and bottom…or all sides


  2. #2
    i thought some of youll have used wsm….and would have a preference on piston to cylinder wall clearance….maybe you havent rebuilt any 650's….thats ok…triples like the ultra or zxi….wsm clearance should be the same when doing a 650….so what clearance using wsm,do you like on a Ultra or zxi 900/1100

    would you go with what the manual says,since they are cast like the wsm pistons….if different material….maybe lees or more….

    the manual says stock oem cast uses .0033 to .0037 pist to wall clearance

    ring gap is .2 to .4

  3. #3
    im not real good at wording questions

    to simplify it better…..

    the manual says stock oem cast uses .0033 to .0037 pist to wall clearance


    ring gap is .2 to .4

    …if you use wsm pistons….would you go with the factory manual,or something different,if so….what do you like?…..i have no spec sheet in the box

    i searched all the treads….wow…they go from .003,.0035,.004,.0045…..and .005….for cast ….wether its oem,pro-x,or wsm……and ofcourse forged going between .005 to .007

  4. #4

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    .004-.0045 piston clearance. Chamfer all ports all the way around. Ring end gap .012 to .016 most ring end gaps check ok right out of the box . Measure piston to cylinder wall clerance at the very bottom of the piston skirt. Brake-in at no more than 1/2 throttle for 2 tanks of gas. then you will be good to go. Tommy Jordan

  5. #5
    thanks Tommy ill drop it off and tell him

    ive got MTC forged pistons in my ZX1195cc ,and Wiseco in 4-wheeler…and my try JE or Cosworth in next bike build

    never heard of WSM until jet skis

  6. #6
    steve45's Avatar
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    I really don't know how you would measure clearance to a ten thousandth. I use a piece of .004" shim stock on the larger engines. I don't know the spec on the 650.

  7. #7
    just so you ,or others come across thread...

    the numbers 2fast4u..... .004 to .0045

    are what wsm says for piston clearance,for kawi 650/900/1100/1200.....all the same....regardless of over bore also...so if you get a .25 or 1mm over....still same piston to wall clearance

    wsm for 550 different .006 to .008 big difference

    heres a photo of WSM spec sheet.... p to w clearance and ring end gap

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    Last edited by moko; 02-14-2017 at 01:27 PM.

  8. #8

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    To measure to the clearance accurately, you measure the piston across the skirt with micrometers and then measure the bore with a bore gauge or ID mics. Then just take the difference. I really wouldn't worry about the last few tenths (.0001).

  9. #9
    steve45's Avatar
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    That's my point, the fourth decimal point is really meaningless because you can't measure that accurately with typical machinist tools. The shim stock makes it easy.
    Last edited by steve45; 02-22-2017 at 08:04 AM. Reason: Typo

  10. #10
    good point guys....i told him .004 ....he usually puts the closer to .005 ,with a cast piston,i felt little tighter was better.....i may try wiseco next time....which are forged and expand more...so i know has a bigger clearance

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