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Gearbox Shimming

Discussion in 'Supersport (1974-2007)' started by Desmoquattro, Sep 11, 2021.

  1. I've had a gearbox whine, like a straight cut gearbox on an original mini. I've taken the cases apart, how important is it that the drum and shafts are shimmed evenly on each side?

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  2. I have shimmed a couple of BMW gearboxes, the procedure with these is, mount the shafts without shims on one side and then shim the other side to take up the slack above the bearing so the shaft/bearing fits snugly into the other side of the case with an endfloat from 0.05 to 0.15 mm.
    We are talking shim thicknes 0.05 to 0.3 mm per shaft on BMW's. Symmetrical shimming on a BMW gearbox is next to impossible because one has to re-remove the shafts, this includes re-heating the case and re-freezing the shafts. Factory BMW manual states to shim on one side after shafts have been mounted on the other.
    Never done a Ducati but common sense tell me the procedure must be pretty much the same, also because the construction looks the same.

    There is one exception on a BMW box, mounting an M94 (1993) input shaft in a M97 (1997 onwards ) case, there one has to shim the input shaft prior to mounting with 1,5 mm!! shim on the bottom to take up the slack because of design differences.
    HTH.

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    #2 NineNineSix, Sep 12, 2021
    Last edited: Sep 12, 2021
  3. That sounds more labour intensive than a Ducati gearbox!
     
  4. When I’ve shimmed my Duc gearboxes they’ve only been slightly out of tolerance and already have shims/thrust spacers on both sides and the ends are all different diameter! I’ve just reshimmed with shims I’ve had available and not aimed to shim each side equal, can’t see that making a difference. I’ve never had one whine like an old mini tho. Give all the bearings a really good looking at..
     
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  5. The Beemers only need reshimming when bearings or shafts are exchanged.
     
  6. "Factory BMW manual states to shim on one side after shafts have been mounted on the other."
    Single side shimming , not to bad, but precise job, can be done in 15 min, XLS sheet to calculate ;-) because I am lazy.

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