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Thread: 1974 Ducati 250 crank shim issue

  1. #1
    Join Date
    20.08.2018
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    Edinburgh Scotland
    Ducati models
    250 mk3
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    Default 1974 Ducati 250 crank shim issue

    I have a 1974 250 single which I am renovating.
    Bought a new samarin 30mm crankpin kit and new piston for the bike, (Lacey Ducati) I have fitted new SKF C3 bearings in the cases. Tried puting crankcase halves together with just a new gasket and no internals, fine, put in the rebuilt crank and closed the cases, fine, bolted the cases together and checked the end float on the crank, =1mm. I have two old shimes of .53 and .32mm that were fitted before.
    Fitted the .53 shim to LHS and the crankcases wont fit together cleanly, it rocks slightly around the crank, same with just the .32. tried the shims on both sides and RHS only, same result, case will not close (about 1mm rock)
    As a test I gently and by hand only, put in a few bolts/screws and as expected the crank was more difficult to rotate so backed off and removed all shims.
    I have just ordered a set of crank shims from Lacey Ducati (was going to measure what I needed then order later) Mr Lacey says this is a fairly common issue and is likely crank shim related, will find out as soon as I can fit the new shims.
    At Mr Lacey's suggestion I checked the original shims, they sit flush on the new (fully seated) bearings and on the crank shoulders, though they are a bit larger diameter than the crank.
    I can't see why the original shims can be causing this but they are, or are they showing up some other defect.
    This is the original crank (new pin) and original cases with new bearings, my bike is a very original complete machine.

  2. #2
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    20.08.2018
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    con rod is not central to case join, normal?
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  3. #3
    Join Date
    27.08.2010
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    scottish borders
    Ducati models
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    Was the crank rotating freely when all bolted up without the shims? Could it be a case of the crank being out of alignment?
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  4. #4
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    20.08.2018
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    Ducati models
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    Yes, the crank spins freely when bolted up without shims.
    I had thought the crank pins may be a bit out of line but if so it would not fit so well through the bearings and let the case close up with free crank spin?
    The crank was rebuilt by an experienced business called Laverda Scozia in Glasgow, he has worked on Ducati singles before and mostly deals with Laverda's so I expect he is expert in this work.
    Just not sure why the original shims could cause this issue

  5. #5
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    Hopefully the new shims will prove to resolve the problem easier than I had with mine http://www.ducati-upnorth.com/forum/...crambler/page8
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  6. #6
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    The LH crank journal is the issue, the main bearing does not sit flush on the thrust face, about 1mm clearance. May need to get the crank pin pressed out again to have the journal accurately machined.
    Putting a chamfer on the inside face of the new shims will have no effect as the orginal shims have a larger (worn) ID and still don't sit flush.
    Anyone got a spare LH crank half

  7. #7
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    Did you measure the width of the crank after it had been pressed? there should be a given size/tolerance in the manual.
    Sam
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  8. #8
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    Looking at my manual it should measure 65.5 - 0.05 that is to the raise section on the crank that the bearing thrust washer sits against.
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