Gearbox with ARRT gear?

[Alex kettle]

I bought a spare gearbox to play around with as my kickstart jams badly and this one came my way cheap.  I’m not the most confident in my skills and never had a gearbox apart so this was new territory for me. I shouldn’t beat myself up so much as now Ive had this one apart and back together it’s not so scary. Still young and learning I suppose. I want to get to know my a10 better so I can build up my confidence.  Whilst having things apart I noticed that some one has penned this gear with 29t  “H” ARRT. Looks like the box has been overhauled and unused it appears to be in good nick. The case is stamped as std so I’m guessing has someone swapped the internals? I’ve heard of the RRT gearbox but not a ARRT. Anybody shed any light?

[JulianS]

ARRT not to be confused with the close ratio RRT box.

The chart below from 1963 gives details.

[Alex kettle]

Thanks Julian that’s a really helpful and interesting chart I’ll have to look and see what else is in here.

[JulianS]

The ARRT box mainshaft has the 14 tooth "G" gear cut as one piece with the shaft -non detachable which does cause a problem finding a replacement if the gear wears.

[Alex kettle]

Julian you are correct about it having a 14tooth “G” gear cut as a one piece shaft and it looks on great condition. The rest of the gears are standard. Does this give me a short first gear then?

[trevinoz]

Same as the STD2 first gear. Good for wheel stands.