Gearbox questions

... which is a good item - generally robust with a slick gearchange. It does have its weak points - particluarly the layshaft bearing in the inner casing. You can find exploded diagrams all over - try here: https://andover-norton.co.uk/en/shop-drawing/516/gearbox from Andover Norton.

I can't remember what the threads on those screws are but helicoils will fix them. Please use the correct thread for the age of the box ie BSF / Whit / BA if it's pre-Commando.

Oil? Straight 40 is a good starting point.

It mentions a box with a number quite close to yours.

https://www.nortonownersclub.org/node/4639

Also, this thread may help disperse any concern that your box is off an AJS or Matchless:

https://forum.jampot.com/viewtopic.php?t=22851

I note Ian's suggestion, but you might also want to consider that the recommendation for AMC boxes fitted to Commandos is EP90.

The box  is probably a  late 1950's Norton box  and  could have come from one of several types of bike . I would get the inspection cover threads welded up and drill/retap back to std .The small plug is the level . drain is underneath. SAE 40 is a good option. Change the oil.

... I use Tracy Tools: https://www.tracytools.com/ For nuts and bolts Nooky's Nuts are reasonable - but not top - quality: http://www.nookysnuts.com/catalogue/catalogue1.html but if you want stainless there are various specialists eg Middleton: https://www.stainlessmiddleton.co.uk/

As already said, inspection cover 2BA. Which I on less precious bikes (BSA) has retapped to M5 (BA2 dia 4.7x0.81mm vs M5=5x0.80). On the RGM website, in section gearbox, they kindly tells dimensions and threads of fittings. Sadly I didn't make notes on threads on latest AMC box I rebuilt. Except that the drain plug is 3/8BSF and the sprocket lock washer screw is 2BAx3/8. About oil. Factory spec was same as engine oil, but gearbox oil EP90 has about same viscosity as 50 engine oil. I use 75W90 gearbox oil in my Nortons.

No idea, just remove the oil level screw and fill until oil starts dripping out. Of course with bike vertical. I guess with both wheels on level ground.

The books say 1 pint.  A touch over half a litre.

I put the bike on the centre stand and fill to the required level ( of ST 90 or Classic EP90 )  by looking at the level plug. I leave the plug tight, so not leak oil, same for topping up. I understand that EP 90 is about the same viscosity As SEA 50, good for Singles engines but the other two I mentioned earlier, better for gear boxes IMO.

Philip H was very helpful with identifying my last project G box (Not matching) It appears these  boxes were made in batches. N for Norton and M for AMC. prefix. So they could be sitting around a while.

What is the engine? asking as you may need proper rebuild manuals for engine and gearbox, depending on what you plan to do in the longer term.

The earlier 5 stud (pulling down the head) speedway engine had an alloy conrod which over time got longer, increasing compression and finally broke. Around -48 or maybe -49 came the 4 stud sporting a steel conrod. Had a 5-stud as my first speedway bike. Later exchanged my 99 for a JAWA. Superior frame and less maintenance.

Gearbox N12664 dates to early 1959. I cannot help with the model of Norton.

Am I right in thinking that an AMC box with the 1960-on closer ratios is stamped N2, then the box serial number?