twin crank balance factor

Discussion in 'Motorbike Technical Discussion' started by info, Nov 28, 2005.

  1. info

    info Guest

    I'm having real difficulty finding the answer to what seems a simple
    question; I need to know the bob weight formula [balance factor] for an
    inline twin [both pistons run in parallel].
    Top rpm is 8500, usually runs at about 4-5000. Street use.

    I'm in India, and my old 1977 Kawasaki kz400 has a stripped balancer
    driving sprocket. This is basically not repairable, but I've had
    correspondence with an American who has had good results by removing
    the balancer shafts and having the crank balanced.
    An old friend of mine is now managing a hi tech machine shop [turbocam
    India] not too far away that is about to buy a balancing machine, and
    he wants to help.
    I need to do the preliminary work at a local shop first, including
    making the bob weights; but are they 1;1 in this case [equal to
    piston/rod assembly] or does reciprocating weight have to be worked out
    separately like on a V8?
    I'm a good mechanic and not bad with engineering. There are some local
    guys who are good as well, but as I said, no one has ever done this
    I'm sure there's a machinist out there in usenet land who knows the

    I bought the old KZ in the US in 1978, and brought it to India in 1982.
    It's respected like an old Ferrari would be in the west.
    It's getting hard to keep it going now, and it looks pretty rough, but
    it still kills any bike in current production in India.
    Thanks for your time, I've been mailing and posting this question all
    over but have had no replies.
    Mark Holden
    info, Nov 28, 2005
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  2. info

    fweddybear Guest

    I'm having real difficulty finding the answer to what seems a simple
    Here's an idea for you.... since it might take alot of work redoing the
    camshaft and all, you might want to find another 77 kawasaki kz400 on
    ebay...... its funny you mention this bike as I had one as well.... I grew
    out of it after a month... I even changed the sprocket ratio so that it
    would be quicker off the line, but the top end sacrificed..... it may just
    be easier to swap engines....

    good luck...

    fweddybear, Nov 28, 2005
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  3. info

    CK Guest

    Ummmm, why not just *buy* a new or used crankshaft and whatever other
    bits you need, box it all up and mark it "machine parts" and have it
    shipped to Indjuh?

    It's not like nuclear weapons proliferation, yannow...
    CK, Nov 29, 2005
  4. info

    info Guest

    The Bike is 27 years old; used parts will be the same age.
    shipping costs to India will cost more than the entire job, machining
    and all.
    you can't put a different crankshaft in without new undersized bearings
    and a crank grind. finding new undersized bearings will be as much work
    as getting the crank ballanced,
    techincal items will get stuck in customs for months; if I ever get
    them at all. you don't mail things like this to countries like this,
    you make do with what's available.
    why do you think I asked the question I did?
    thanks anyway, Mark
    info, Nov 30, 2005
  5. info

    CK Guest

    It's not at all uncommon for an idle dreamer to come in here and try to
    pick the brains of anybody willing to spend time answering their
    endless questions. They often want a free education in mechanics and
    technology and turn their inital odd question into a long, drawn out
    debate to show that they are smarter than the people wasting their time
    helping them. I won't mention any names.

    But, since your problem is so uncommon, you may have to do your own
    research into balance factors for vertical twin engines. I saw one
    website where a fanatic was installing an XS-650 engine into a late
    model Yamaha aluminum frame. The guy also changed the crank from 360 to
    270 so it would fire like a Yamaha TDM. I would think that guy knows a
    lot about rebalancing vertical twins.

    Google up XS650 and Mark Olson in this forum to find the link to the
    XS650 forum.
    CK, Nov 30, 2005
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