Upright gearbox, top fixing bolt

There is a proper spanner for the job.

I also have a1948 es2 and struggle with altering the primary chain tension! Where can this spanner be purchased ? Presumably the number quoted is a suppliers reference number, it would be very useful to know where such supplier can be located please.

I've always managed to get on my 1934 Inter with a regular combination spanner. The angle on the ring spanner end is just right to clear everything. I'm guessing the post war Nortons had wider mudguards though, so could you warm up and bed a spanner to suit the job?

My tool kits are full of specially modified tools, and it's always worth picking up a few of the more common sizes at autojumbles so they can be modified as and when.

The number that I had scribbled on the background is the pre-war Norton part number for the toolkit spanner. I believe that the post-war number was A2/576

I don't know of anyone making and selling them. Beaulieu or eBay are the best options or perhaps Vintage Tool Company has some ?

Some have 'Gearbox Top Nut' cast on them.

The extended nut on the gearbox top mount should be fitted on the left hand (primary chaincase) side. Some battery boxes make it easier than others to get in there (WD16Hs are particularly limited).

I have a 35 Inter and a 37 mod 50 with dolls head gearboxes. It is indeed convenient for adjustment to have the nut behind the battery carrier but if you want to remove the gearbox, you have to get the bolt out of the top bracket. This is prevented by the dolls head and will need removal of outer and inner cover first!. Best to have the nut behind the dolls head. I bought a £1 combination spanner from Kempton jumble and ground away the open ended 'ears' until I could get a bite on the nut and a fraction of a turn. Working from in front of the oil tank, put the gear linkage into fourth gear to give more movement/clearance. Slow job but works, as I found out in a pub car park on our 'mouth to mouth' 2000 mile run!. Probably possible to work from behind and in front of the oil tank. Seem to remember no clearance to use the ring end...cut it off. I also think that there is a flat on the gearbox casting to indicate that this is the correct way round but may be wrong and the bikes are too oily to look.

Excellent! In times past there were numerous different shapes of spanner. Now they are all made to one standard design and proportion. Not really an advance on olden days!

My 1947 has the nut on the chaincase side, slackening and retightening is easy, just remove the battery and use a standard open ended spanner. I later bought a 1948 Inter with the nut on the gearlever side. What a pain to try and adjust. When I had the bike stripped down I took the opportunity to change things around. Unfortunately to reverse the direction of the bolt you have to remove the gearbox inner cover, but this is well worth doing as it gives you the chance to inspect the gearbox innards at the same time. Once this is done, primary chain tensioning is so easy.

I know that assembly line techniques have changed dramatically over 80 odd years but I assume that the factory built complete gearboxes and then installed them into frames.  I cannot see them assembling gearboxes in the frame, which would be necessary if the nut were on the left. That is the reason I fitted the upper bolt nut on the right side. With the angled tool  it is possible to adjust. Engaging 4th gear gives a bit more wriggle room around the linkage.

I know that the WD1H book has a line drawing showing it on the left but there is no text instruction to remove or refit the battery. Was this a wartime fix to overcome the fact that the cranked spanners got lost or were misappropriated?

I I can see merits to both arguments.  Down to the individual I guess.

I was lucky to find the correct spanner on Ebay. It does make adjustment easy. Mine does have  'Gearbox Top Nut' cast on it.