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  1. #1
    scorp's Avatar
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    ?? Line Boring Crankcase

    Hello all, (2000 SLX 1200 carbed engine)

    Shut down on the water this summer, took it apart found a seized crank (center bearings fried)
    and dug into crankcase a little. sent crank out for rebuild and looks like case needs work too, I put a straight
    edge across and there are pivot points. so my question is it worth having it line bored? or find a nice used
    case instead? and just out of curiosity when you have the case line bored will the crankshaft still fit properly or do you need oversized bearings? what is the average cost for line boring and who does it?

    Thanks,

    Happy Holidays!!!!!


  2. #2
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    Post up some pics of the damage. Im sure there is someone who can machine the cases. I don't know how much that would cost. I would probably just look for a set of cases.

  3. #3

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    What is the damage exactly?

    Do you bearing journal damage or case sealing edge damage? Bearing journal damage would probably mean new cases, sealing edge damage might be able to be repaired but I would probably look for new cases there too.



    Quote Originally Posted by scorp View Post
    Hello all, (2000 SLX 1200 carbed engine)

    Shut down on the water this summer, took it apart found a seized crank (center bearings fried)
    and dug into crankcase a little. sent crank out for rebuild and looks like case needs work too, I put a straight
    edge across and there are pivot points. so my question is it worth having it line bored? or find a nice used
    case instead? and just out of curiosity when you have the case line bored will the crankshaft still fit properly or do you need oversized bearings? what is the average cost for line boring and who does it?

    Thanks,

    Happy Holidays!!!!!

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    I had my MSX 140 crankcase line bored, maybe two years ago. Bearing had spun and eaten into the bearing support metal. Cost to have the line boring done was not huge, I am thinking it was maybe $200 ish?

    What happens (in my experience, anyways) is the case half is shaved/decked down some thousands of an inch, then the case halves are assembled dry and torqued together, empty. The line boring machine then drills right through the center of the old bore axis, but since the case halves are now slightly closer together the line boring removes some metal from both top and bottom of the bearing support surfaces, creating smooth fresh metal bearing zones.

    Then you install the rebuilt crankshaft with standard bearings. The line boring, if done properly, ensures the crank will sit straight in the cases.

    The only catch is that since the crankcase has been effectively 'shortened' by a thin fraction of an inch, the assembled engine overall is now slightly shorter, from cylinder head down to crank case painted bottom.
    Last edited by K447; 12-20-2014 at 11:00 AM.

  5. #5
    scorp's Avatar
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    Thanks for the info guys,
    k447 thanks for explaining how line boring is done, I had no clue, based on that, I need new cases,
    same thing happen with the spinning and eating into bearing/ journal support metal, there's about
    a good 1/16th of inch of metal eaten into top and bottom. Really sucks cause the case is in excellent
    condition otherwise, and from what I've seen online some of the cases going for a premium,
    look like crap.

  6. #6

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    if you have it line bored like k447 then they shave the cases and rebore them and your then will need thicker cylinder base gaskets to make up the difference or you can double them up like some guys do . I have a bunch of different thickness base gaskets that watcon used to use if you end up needing any. I would just buy a set of used cases

  7. #7

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    The only catch is that since the crankcase has been effectively 'shortened' by a thin fraction of an inch, the assembled engine overall is now slightly shorter, from cylinder head down to crank case painted bottom.
    and your squish ends up tighter and your port timing is off also all is fixable but it's cheaper to buy cases
    Last edited by K447; 12-20-2014 at 11:00 AM.

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  9. #8
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    Quote Originally Posted by 785 lugs View Post
    The only catch is that since the crankcase has been effectively 'shortened' by a thin fraction of an inch, the assembled engine overall is now slightly shorter, from cylinder head down to crank case painted bottom
    .


    and your squish ends up tighter and your port timing is off also all is fixable but it's cheaper to buy cases

    All very true and dependent on how much was machined off the cases. .002 machined off shouldn't make much difference, but .010 would make a considerable difference.
    Last edited by K447; 12-20-2014 at 11:01 AM.

  10. #9

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    Quote Originally Posted by BryanP View Post
    Quote Originally Posted by 785 lugs View Post
    The only catch is that since the crankcase has been effectively 'shortened' by a thin fraction of an inch, the assembled engine overall is now slightly shorter, from cylinder head down to crack case painted bottom.


    and your squish ends up tighter and your port timing is off also all is fixable but it's cheaper to buy cases

    All very true and dependent on how much was machined off the cases. .002 machined off shouldn't make much difference, but .010 would make a considerable difference.
    exactly but I doubt if there damaged at all you could get away with less then .010

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  12. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by 785 lugs View Post
    Quote Originally Posted by BryanP View Post
    Quote Originally Posted by 785 lugs View Post
    The only catch is that since the crankcase has been effectively 'shortened' by a thin fraction of an inch, the assembled engine overall is now slightly shorter, from cylinder head down to crack case painted bottom.


    and your squish ends up tighter and your port timing is off also all is fixable but it's cheaper to buy cases

    All very true and dependent on how much was machined off the cases. .002 machined off shouldn't make much difference, but .010 would make a considerable difference.
    exactly but I doubt if there damaged at all you could get away with less then .010
    Perhaps it is possible to have the damaged bearing areas built up with additional aluminum material, then do the line boring. Not my area of expertise, however.

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