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Thread: Shim stock for front motor mounts

  1. #11


    Millwrights have been using the shim type shown in the ebay listing to align coupled shafts for years. They're available from industrial suppliers like McMaster-Carr for about a buck apiece.

  2. #12
    Join Date
    Nov 2009
    Baltimore, Maryland


    Another quick question. My guage indicates a gap of .021. I want to make sure that is a "normal" gap for a front motor mount on a knucklehead.
    Eric Hitzel
    AMCA 14954

  3. #13
    Join Date
    Sep 2013


    Thats in the ball park.

  4. #14
    Join Date
    Jul 2002
    North Hills, CA and Pine Grove, CA


    I have never seen a bike come from the factory with shims. Nor have I have ever used them. Shims under the generator is another story.
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  5. #15
    Join Date
    Nov 2008


    I'm with Chris on this one. There is a "shim" under the motor for the BT flat heads but it goes under both front motor mounts and is more like a strap # 24795 for fitment in 48 and up frames. As I recall it is about 1/8 " thick. I have never used shims on any knuckle motors. You do need to make sure that the motor mounts and frame are "decked" to make sure they do sit on each other flat and true and that the hoes are not wallowed out and line up.

    Tom (Rollo) Hardy
    AMCA #12766

  6. #16


    I just ran across a galvanic corrosion design guide at work today. According to the table, in a harsh environment, there should not be more than 0.15 V difference in the anodic index for dissimilar materials.
    Cast aluminum containing Silicon is rated at 0.90V, non-Si cast Al 0.95V while carbon and low alloy steels are 0.85V. So even in a high humidity and salt environment, there should be little to no galvanic corrosion between the motor case and frame. Shims, if used, should be steel.
    (As we could have surmised, as these bikes have been on the road for 70 years already without adverse effect)
    Quote Originally Posted by wideglide38 View Post
    I agree dissimilar metals can have a galvanic reaction and have experienced it within the electrical industry. However, I wondered with steel frames and sand cast aluminum cases, did the MoCo treat or coat hardware/shims/frames/cases to prevent a galvanic reaction? My concern coating parts is the potential reduction or elimination of ground continuity which is needed for circuit breakers, etc. Just my 2 cents and wondered what others have experienced.

  7. #17
    Join Date
    Mar 2005
    Huntington, New York - American Zone


    In over 40 years, I've never used shims under the front motor mounts and have never broken a front case casting. Also, the gavanic potential between 304-320-type stainless steel (like a feeler gauge) and aluminum is very low. If you coose to shim, I wouldnt worry at all about corrosion between these two metals.
    Bill Pedalino
    Huntington, New York
    AMCA 6755

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