Crushed Aluminium Frames - excessive tightening

Discussion in 'General Questions' started by Fabian, Sep 14, 2009.

  1. Fabian

    Fabian Well-Known Member

    G'day all

    This thread is a starter topic for the subject of excessive clamping force applied to frames when installing a motorised conversion.

  2. Fabian

    Fabian Well-Known Member

    The discussion started from this thread:

    My advise (even with steel frames) is not to drill into, or cut into, or apply excessive clamping force to front engine mount fastened to lower downtube, connecting headstem with bottom bracket, when installing a motorised engine kit.

    My next door neighbour decided to convert his mountainbike after having a ride of my bike - he was going bananas on the thing, never smiled that much in a long time.

    After purchasing the engine kit, i warned him NOT to apply U-blots directly to the frame and also devise something to sit inside the U-bolt, spreading compressive pressure over at least a one inch area - similar to the method used on my own mountainbike.
    I mentioned that most large diameter aluminium frames are paper thin and crush or split with the slightest of ease.
    I also mentioned to attach rubber strips or a good couple layers of gaffa tape to the backing plates in adding a much better frictional coefficient between metal clamps and painted frame surface.

    A day later, and after he over tightened his attempt of a bracket that was not curved to the profile of his downtube and not using rubber backing material, my question was: WHY & HOW" and "you seen how i fabricated the mounts on my bike, why didn't you just copy the idea"

    The answer was: I didn't think it needed to be curved & I didn't really feel the nuts on the U-bolts coming under and pressure so i just kept tightening up the U-bolts.

    My only advise to people who are going to convert a bicycle with a motorised kit - just have a look at my posts and other peoples posts on methods of making safer engine mounts that don't crush or split frames.

    Photos show the result of not following instructions:


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