Gearbox Identification

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Nortons put out a service advisory/bulletin when the 2nd version of AMC gearbox appeared,
warning also not to mix the different types of gears and always to install them as made pairs.
Anyone got that handy, to quote from exactly. ?
 
According to Bacon, "the sleeve-gear pair, the mainshaft second and layshaft third were changed in 1960 (AMC 2 appearance). This returned the third-gear ratio to its earlier value and raised both first and second a touch. At the same time the layshaft top and mainshaft second were given new part numbers while remaining the same physical shape and interchanging with the earlier items."
 
Roy Bacon researched/wrote that a long time ago.
A lot of Commando info and finer detail has come to light since then.

Somewhere (on the NOC Forum ?) was a brief detail on the different tooth forms.
If you photograph the gears side-by-side, the difference is visible.
The page(s) on gearbox tooth counts and numbering and shafts etc seems to have become members only too ?

Anyone got those Norton advisories/bulletins. ?

I've got an early MA box I need to open, could photo the gears.
 
I plan to use the N#### gearset in a Commando. I may use the N#### shell as well. I keep hearing the gears and the shell are too weak. Can somebody please point me to where these weaknesses are documented, and when or how they were rectified? As far as I can find out, the early gears and shell are no weaker than those used in the first couple of years of Commandos.
Click to expand...
Unfortunately not but I have an 'N' shell and gears in my Commando with 39k miles of my abuse on them. Worn 1st and 4th sets replaced along with 2nd lay which was starting to drop out of 3rd. I can't find the reference but I recall reading that the early pre Commando housings used a better aluminum. However, that could well be old wives gossip. What I do know is that the current housing is in very good shape, no inter bearing cracks (just stripped and renewed quad and selector bushes). I also have a similar spare in as good condition.
 
Stephen Hill said:
Norton boxes stamped N#### were built from 1957 - 1962.
Norton boxes stamped NA#### were built from 1963 - 1968.
Click to expand...

May we ask where this info comes from ?

The 1962 parts book lists different part numbers for 1960 and for 1961 gearboxes, and quotes a number for the changeover.
Looks to be something to do with clutch actuation (mainly ?), without investigating any further.
The change is visible externally.
 
The main difference I could detect from N to NA is the kick start shaft return spring and length of the bush in the intermediate cover are different.
The cases DID grow beefier as time went on. With at least 3 grades within the commando series alone.
Different/improve hardening of the gears (AH) within commando .
I own 15 AMC gearboxes on the shelf and another half dozen in bikes through MKIII 75. I am missing the 50's versions but have at least one "N" and several "NA".

Personally I would never use an early gearset or case in one of my commandos. 73 & 74 are the best, 75 is too specialized for general commando use. IMO
 
looks to me like the only fix is a fresh start on all the main topics, unless someone beats me to it,

i'll be putting up "crank porn deux" - loved that thread when i first stumbled on it

https://www.accessnorton.com/NortonCommando/commando-crankshaft-porn.7673/#post-97929

the pix issue alone courtesy pbucket has mangled a great deal of prior efforts, dunno if the additional dead links thing, within the forum itself is fixable..

that original vincent engine rebuild thread was awesome with the supporting pix now all gone
 
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