Hello All,
I have a bit of a bitsa and i am after some information. Is the mk2 & mk3 gearbox shell mounting lugs dimesionally the same in terms of widths?
If this question is too hard to answer then could someone provide me the measurements for mk3 lug widths.
Reason i am asking is that i have 2 cradles and the inner dimesions are different (measured adjacent to the Isolastic tube to rule out distortion)
I would like to know if this is by design or simply 70's manufacturing tolerances
Thanks,
Adam
Gearbox shell width is the…
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I found that...
... document very interesting. But I struggle to understand that a misalignment of .029" between steering head and swinging arm can cause the rider to wear out a set of handlebar grips in one race. Surely the flexibility inherent in the tyres at least would give more movement than this? And even the metalastic s/a bearings in a Featherbed would deflect a greater amount.
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The MK3 cradle modified with…
The MK3 cradle modified with extended slots to allow gearbox movement is a common upgrade to pre MK3 bikes due to the added cotter pins to support the swingarm pivot shaft. I have one on my 72 and there are no gearbox fitting issues. So any variations you see is down to 'Quality' or more likely no quality.
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AMC gearbox width
ALL Commando
3.18" top + washer
3.31" bottom
featherbed/
3.31" top and bottom
very minor differences occasionally from wear.
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Gearbox shell width is the same across all Commandos (and probably earlier twins). There is a spacer on the top bolt to bring it out to the same width as the bottom mounting.
Measuring some old Mk2A engine plates, I get 84mm +/- 0.3mm (they've had several coats of paint) which matches the gearbox shell width.
This https://nortonclub.com/docs/Straightest_Commando_Frame.pdf might be of interest to you.