Lightweight gearbox number prefixes

[Ozmadman]

Just a thought, I have posted some info for a member all to do with lightweight main shaft/changes and part numbers based on gearbox number but does anyone know how to tell in the first place whether the box is from a 250 or a 350 as the actual numbers could be from either if there are no other identifying marks? is it to do with the prefix. For example, I have a spare gearbox which came with the bike(I was told it was from a 350) and which I have rebuilt, ready to put in the bike at some point, then I will rebuild the other one. The gearbox number is M3043 and presuming that the internals are original, this would put it into the early type (early type main shaft)for both a 250 and a 350. If it is from a 350 then it should go straight in as my other box is also an early one. If it is from a 250 then I am stuffed and will have to pull it apart again to change the main shaft. Is there really no other way to tell which it is except by either measuring the main shaft dimensions or finding out the hard way and removing the old box only to find out you have the wrong main shaft. Also, maybe an idiot question but I presume that the diagrams in the workshop manual pertain to the clutch end of the main shaft bearing in mind both ends are threaded.

Many thanks

Paul

[les ward]

During my time as machine dating officer I learnt that 250 gearboxes had the prefix G and the 350 had the prefix M. Why they used M is a puzzle, as it is also the prefix for the heavyweight AMC gearboxes.

Your number looks early 350cc to me and I would guess late 1960 or early 1961. I would get in contact with Roy, as machine dating officer, and he should be able to look it up for you.

[Ozmadman]

During my time as machine dating officer I learnt that 250 gearboxes had the prefix G and the 350 had the prefix M. Why they used M is a puzzle, as it is also the prefix for the heavyweight AMC gearboxes.

Your number looks early 350cc to me and I would guess late 1960 or early 1961. I would get in contact with Roy, as machine dating officer, and he should be able to look it up for you.

Thanks Les, very helpful

Paul