Benelli 2C: Crankshaft seal fix
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Thread: Benelli 2C: Crankshaft seal fix

  1. #1
    Member #
    Join Date
    Feb 2010
    South Australia

    Benelli 2C: Crankshaft seal fix

    Hi all,

    Just recently, one of the five Benelli 2Cs that we restored died after pushing its crankshaft seals outwards. This had some damaging consequences - the left hand seal ended up loose on the shaft inside the flywheel and tangled up with the generator coils ripping them off and cracking the flywheel magnets. Quite a mess. I spoke to some of the New Zealand 2C racing guys and apparently this isn't uncommon when the bikes are raced - not that we were racing! The racers fit seal retainers on their motors to ensure the seals stay put.

    Anyhow, based on their advice we rebuilt the bike and made the following modifications:

    (1) The outboard crankshaft bearings were replaced and we used the same spec bearings but selected the type with a small groove in the outside shell for a thin o-ring. Once the crankcase halves are joined this holds the bearing firmly in place and a splash of Loctite Bearing Mount on the crankshaft makes sure it stays where it should.

    (2) Despite being told that the original 10mm thick seals were no longer available, we were able to source these at a good bearing shop. Do not use the standard off-the-shelf 7mm seals.

    (3) The photos below show the seal retainers we made. The LH side (magneto) uses two tabs (to allow the plate to move for timing adjustment) and the RH side uses a simple large washer. Both are affixed with 4BA screws. These are not metric but they had the lowest head profile I could find (approx 1.25mm). Loctite is used to secure the screws.

    If you are doing a full engine rebuild you might like to think about this mod. We are about to check the other four bikes!


    Attached Thumbnails Attached Thumbnails Benelli 2C: Crankshaft seal fix-crank-seal-lhs_s.jpg   Benelli 2C: Crankshaft seal fix-crank-seal-rhs_s.jpg  

  2. #2
    Member SPEIRMOOR's Avatar
    Member #
    Join Date
    Apr 2013
    New York USA
    Nicely done, thanks for sharing


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