Gearbox number

Hello Glen. Usually the gearboxes stamped N or NA indicated that they were originally installed in a Norton motorcycle, as the Matchless gearboxes were often stamped M or MA.

The gearboxes stamped "N" were usually fitted to the 1962 and earlier machines made at the original Norton works, later when AMC took over manufacture of Nortons they started stamping "NA" on the gearboxes. The gearboxes on my early slimline Nortons from 1961-62 have numbers in the low 20,xxx, so your gearbox might be from about four or five years previous to this, a GUESS on my part would say that it is from around 1957 give or take.

Neil.........you raise a good point as quite often, on this WebSite, owners ask about the production date of an individual Norton Gearbox. 

Prior to Bracebridge closing down, all production bikes came with a shop number for engine. frame, gearbox and forks. Presumably this would help ID a production date if a particular part failed in service.  AMC seemed to generally abandon this practice until the Commando and Mercury models appeared.

Even with the shop numbers available is not easy to exactly date when a particular gearbox was assembled. These were generally put together in huge batches and then dumped in store rooms until needed. Sometimes there could be a two year gap between manufacture of a gearbox and use. This year I have been researching Model 77  and Nomad production years. Your box appears in my notes around September 1957. So it could have gone into an 88, 99, Nomad or 77.

Thank you for the second time tonight.

Main issue was pre or post 64, so you have answered the question. (For the overhaul kit)

Further, I think we are now a bit wiser as to how this came about regards earlier AMC boxes.

Thank you.

Maybe I should have stripped the box down first, before ordering parts?

But Phil's response was educational too.

Thanks.

Internal gear ratio's changed  pre 60  sometime .

I usually run with what is in the box, but start with a 20T gearbox sprocket.

Then if not right I can either go back down to 19T or change the engine sprocket.

Works for me.

Robert is quite correct about the internal gear changes which created the AMC 2 box used in the post 1960 Dominator range. Attachment shows revised gearing. The outer, inner and kickstart spring plus its fixing position also altered. The problem with these AMC 1 & AMC 2 gearboxes is how easy it is to mix and match chunks. Like with the Norton Timing Cover there are multiples of options for the gearbox outer cover if you include some AJS/Matchless, Commando, Dominator and Mercury versions. The clutch cable entry point wandering all over the place to begin with.

I once purchased a Norton box which the owner had dismantled and could not remember how to re-assemble. He said that it was an AMC 2 box. It wasn't but for a £100 it was still a bargain and the gears and bearings all turned out to be in mint condition. A small investment in different outer and inner covers plus a new kickstart spring and 23 tooth output gear converted it to near AMC 2 status and suitable for my 650 Cafe Racer.