Atlas gear box?

Have a used gear box. Number stamped on it is NA20709. Not on the lug like a Commando but on the side of the case. Casting is 040122. Any idea what year it is and what years and models it is compatible with, like Commandos?

Hey Htown16, yep believe that’s an Atlas box. Have one myself ; understand the only difference is a Commando main shaft is slightly longer - for circlip engagement - but as it’s interchangeable with Atlas you can have yourself a good to go spare . Jobis on my “to do” list.
Those with greater knowledge will confirm or correct my “info”.
good luck
TBW

TBW said:

Hey Htown16, yep believe that’s an Atlas box. Have one myself ; understand the only difference is a Commando main shaft is slightly longer - for circlip engagement - but as it’s interchangeable with Atlas you can have yourself a good to go spare . Jobis on my “to do” list.
Those with greater knowledge will confirm or correct my “info”.
good luck
TBW

Click to expand...

The Atlas top lug is the same width as the bottom one, when the commando top one is 1/8 (ish or 3mm) less so needing the same width spacer , tus allowing the gearbox to wiggle easily , that plus the different mainshaft , and may be (according to years ) the different kick spring , and different gears teeth number (still according to years ) ..............

marinatlas said:

The Atlas top lug is the same width as the bottom one, when the commando top one is 1/8 (ish or 3mm) less so needing the same width spacer , tus allowing the gearbox to wiggle easily , that plus the different mainshaft , and may be (according to years ) the different kick spring , and different gears teeth number (still according to years ) ..............

Click to expand...

And if it has the earlier kick start spring, then a different outer cover ( it will already have the hole threaded clutch cable)

I have am earlier gearbox. The lugs are the same width top and bottom, and the same as the rear mounts on the 850 motor.
You have a choice - either replace the mainshaft with one from a Commando, or fit an earlier clutch with a single row primary chain and engine sprocket which is what I did. When I bought the 6 speed TTI box, I found the main-shaft was that bit longer, so I had a sprocket carrier made, and now use floating Jawa speedway sprockets as the engine sprocket. For racing, there is a need to change the overall gearing quickly, so I have got 4 with one tooth more on each as they get bigger The biggest one has 24 teeth. The earlier clutch copes quite well - I have never had a problem with it.

Don't forget the outer cover for a commando box has a slightly different clutch cable entry point than the earlier box

So the case can be used in a Commando if you leave the spacer out?

htown16 said:

So the case can be used in a Commando if you leave the spacer out?

Click to expand...

Basically yes
It'll be harder to fit in the gearbox cradle though I'd guess

Earlier main shafts are longer do not have a provision for the drive side nor do the later shafts, the main shaft can be replaced, I think, with the Commando m/s. The outer case cover has a clutch cable entrance/exit hole that is aft of the Commando hole such that the cable will hit the battery box. Additionally there may be a gear set or two that are not compatible with the Commando m/s, 'can't say as I have not (Yet) tried to mix one with the other.

There may be other differences that members will be more familiar with, but this will be a tough row to hoe and could be expensive.. I'd be interested in how this episode concludes.

Best

baz said:

Don't forget the outer cover for a commando box has a slightly different clutch cable entry point than the earlier box

Click to expand...

This is so true... trying to fit the cable with the entry directly below the rear ISO is a real bugger... i replaced the incorrect cover in the end

It's just a spare bare shell. I was going to put it on ebay. Just wondered what it fit.