The Norton Commando 4 speed gearbox is an ancient design that dates
to 1935, with a revision in 1956, it became the ubiquitous
AMC gearbox. It was designed for a 30hp, 500cc engine.
One of the first mysteries I encountered was the "mystery
(in red below) for removing the clutch body lockring. It seems the
tool was available at sometime, somewhere as it is pictured in the manual.
I made my own tool out of a used lower fork bush,
as my first attempt with a screw driver and hammer resulted in
a small chip flying off the lockring! I don't recommend this
About half and hour spent with a saw and a file was all that was
needed to fashion the tool.
The bush was then squished in a vise creating a slight oval to
make it wide enough.
Turn the tool with a large pair of pliers or pipe
L to R: tool, lockring, clutch operating body.
I has discovered lots of "gold" in the gearbox oil, my
original plan (hope) was to renew the bearings and bushes.
The inner mainshaft
sleeve gear bush (above, bottom right) had migrated
to the outer bush, and was 3/4 gone (the source of my gold). 3 bushes
will be fitted as outlined in the Commando Service Notes.
Inspection of the gears revealed, surprise, more neglect and severe
A close-up of the first gear failure (bottom left in the photo
Pitting, scoring and deep grooves and uneven wear are signs
of gear failure.
The gear face failure is most likely from the wrong oil weight
- or no oil at all.
Four new gears are on the way.
Gearbox stripped and cleaned ready for new bearings.
Main bearing showed signs of spinning in its seat (shiny burnished
outside), Loctite was used on the new bearing.
No signs of cracks in the case between the two bearing seats.
|Layshaft roller bearing
|Mainshaft ball bearing
Inner cover stripped, cleaned and polished.
I hope a renewed gearbox will help put the Fast in Fastback.