bent crankcase stud

Discussion in 'Motorbike Technical Discussion' started by krusty kritter, Aug 11, 2005.

  1. '81 KE125 crankcase fiche shows four 8mm X 70mm

    It's kind of *hard* to bend an 8 millimeter stud that's less than three
    inches long. It's about 5/16th diameter. Maybe somebody *dropped* the
    engine and it landed on that stud?

    You could try double-nutting the stud and turning the lower nut
    carefully to see if the stud will unthread. But, for all you know,
    Kawasaki used Loctite on the stud. It might help to heat the stud with
    a propane torch.

    And, maybe you might try welding a nut onto the end of the stud so you
    can turn it that way. You can get into a world of problems trying to
    remove that stud if it's corroded into place. Like, you could mess up
    the crankcase half.

    Is it really bent *that* far? Can you slide the cylinder over the studs
    with a little effort? The other three studs that aren't bent should
    locate the cylinder adequately...
    krusty kritter, Aug 11, 2005
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  2. Hi all sorry if the terminology is wrong, I've just bought my first bike
    and rebuilding it. (A '81 KE125) anyways, I got my new cylinder in the
    mail yesterday and even though im not really ready to assemble the top
    end, I wanted to slide it onto the studs just to see what she'd look
    like. and lo and behold one of the studs is bent. Is there a way I can
    bend that stud back straight or should I just replace it?

    jellybean saint, Aug 11, 2005
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  3. If you're planning to split the cases, you might as well have a new rod
    bearing installed in the crankshaft.

    Exposure to the elements isn't good for the rod bearing. If it has
    specks of rust breaking through the hardened outer layer, the needles
    will begin wearing quickly when you run the engine at the high RPM
    required of 125cc engines. Small 2-stroke engines need clean air
    filters that don't pass any dirt and they need light weight 2-stroke
    oil so the needles don't stick to the rod journals and skid on start
    up. That wears the needles flat quickly.

    My friend once loaned me his Yamaha 125cc AT-1MX to ride in a 27-mile
    hare scrambles. It only made about 14 miles before the rod bearings
    completely disappeared. I had to pay for the repairs, but I suspect he
    knew what was happening to the bearing when he loaned me the
    krusty kritter, Aug 11, 2005
  4. some friend :/
    Arcadefreaque, Aug 11, 2005
  5. I haven't tried to force the stud so that the cylinder will go on as im
    not that far into the rebuild, the engine sat outside with the top end
    off for a while before I got it so I need to split the case to make sure
    that the crank is clean ie. no leaves and water etc. but it may go, if I
    place the other three studs just in their holes, i can see about half of
    the other stud through its hole, so i should be able to knock it on, I
    was just concerned that it would maybe cause some sort of stress where
    it shouldn't. This is my first motorcycle/engine project so I dont want
    to make any big mistakes just becuase I was afraid to ask...

    thanks for the tips, I will just leave it for now and worry about it
    when I get to the re-assembly stage.
    jellybean saint, Aug 11, 2005
  6. It may be that what you're looking at is a botched helicoil job.

    What happens sometimes (DAMHIK) is that the aluminum threads
    for the stud will get stripped and the casing will be repaired
    with a helicoil.

    Because of the length of the stud, if the helicoil drill and
    tap is off by even a very tiny amount, this can translate
    into an appreciable distance at the end of the stud.

    I discovered this the painful way. I was close enough that
    I was able to reassemble the engine, but just barely close

    You might want to unscrew the stud and check it on a good
    flat surface to find out if it's the stud or the hole thats
    screwed up. If it's the stud, I'd replace it.

    If it's the hole that's at fault, I'd probably try to reassemble
    using a little pressure on the stud to get it lined up. I wouldn't
    attempt further repairs unless I absolutely had to.
    Rob Kleinschmidt, Aug 11, 2005
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