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  1. #1

    HELP Is this a std bore piston or not

    I'm pulling my hair out with this one, and I'm probably just an idiot. Just looking to replace 2 pistons on my 1050, as the third had to be bored, 0.50 over.

    What does 81.38 on the top of the piston corralate to as far as size to a new one. Local shop says it is standard but was hesitent.

    Here are the measurements that I had gotten.

    Piston 81.4mm or probably the 81.38
    Bore 81.6mm (Honed to)

    So what piston should I be buying. And what brand, the shop spoke high of wsm.

    Thanks


  2. #2

    Join Date
    Sep 2006
    Location
    topeka,ks
    Posts
    3,332
    uhhh did you contact me on ebay ?

    81.38 is .50 over bore 81.38 plus the missing .12 is the clearence of the piston , is 81.50 mm your machine shop must be meteric stupid


    you never contacted me on ebay back

    i got 3 .50 over pistons

    my boxs were messed up at the machine shop so i had to reuse some of my 81.25 mm piston boxs ,

    2 are the same 1 is a odd ball

    the only difference in them is that the 2 have oiling holes for the wrist pin


    stock is top quality
    wsm is runner up
    sbt is bottom barrel

    the odd ball is on ebay

    the two i was holding for friend that hasnt contacted me back but he still has dips

    lemme know

    the clearence on these should be around 6-7 thou for wsm its what it says on the little paper , and stock iv hurd is 5-6

    the three pistons veri with in 2-3 grams of one another even the ones that match

  3. #3
    So are you telling me that a 81mm piston .50 over measures out to be ~81.38mm and the rest is clearance??

    So if thats the case and I buy (oh by the way it wasn't me on ebay) a wsm 50 over piston and my cylinder bore is 81.6mm I would take that difference and it should be 6-7 thousands?

    Basically

    81.6mm - 81.38mm =.22mm =~9 thousands which is too much

    Is this right?

  4. #4
    bnasty's Avatar
    Join Date
    Apr 2007
    Location
    Texas
    Posts
    225
    Quote Originally Posted by problown89gt View Post
    So are you telling me that a 81mm piston .50 over measures out to be ~81.38mm and the rest is clearance??

    So if thats the case and I buy (oh by the way it wasn't me on ebay) a wsm 50 over piston and my cylinder bore is 81.6mm I would take that difference and it should be 6-7 thousands?

    Basically

    81.6mm - 81.38mm =.22mm =~9 thousands which is too much

    Is this right?
    For your motor, STD is 81mm, and piston to cyl wall clearance is .14mm. It sounds like it was bored/honed 0.25mm over, and has worn for quite some time. Or it wasnt done correctly (if that top end of that cyl was done relatively recently). What I would do is go the next size up, to .50mm over, and hone/bore to about 81.48 and check the piston fit within the cylinder. I just did this for my 750, and I think I have it down so far!! (This is the second top end, the first one didnt go so well)

  5. #5
    Quote Originally Posted by bnasty View Post
    For your motor, STD is 81mm, and piston to cyl wall clearance is .14mm. It sounds like it was bored/honed 0.25mm over, and has worn for quite some time. Or it wasnt done correctly (if that top end of that cyl was done relatively recently). What I would do is go the next size up, to .50mm over, and hone/bore to about 81.48 and check the piston fit within the cylinder. I just did this for my 750, and I think I have it down so far!! (This is the second top end, the first one didnt go so well)

    It all makes sense except for the bore, 81.48?? Its already 81.6mm. Or am I reading something wrong?

    Thanks

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