commando/amc gearbox options/compatability

84ok · Mar 20, 2018

i'm always on the lookout for gearbox/parts suitable for commando use but not clear on what all parts may be compatible?

just looked at an ebay ad that showed a box for use on commando 68-74 understanding the e/start 75 is diff from the rest

that mean an atlas, or other norton model use of the tranny wont work? or other uses of the tranny in other makes & models that use it, or any other parts?

i think the cases or mounting shells when used on other makes can be incompatible with commando

what all is usable for commando years 68-74?

some info
http://www.petersclassicbikeparts.nl/contents/en-us/d142.html

ASSOCIATED MOTORCYCLES ie AJS, Matchless, Norton, Francis Barnett and some smaller makes designed this gearbox and used it on most machines 1956 on. (Also the big Enfield twins) This is probably by far the best transmission for a British bike. Most parts are available new

http://preservationcycle.com/index....-norton-commando-gearbox&catid=86&Itemid=1739

https://www.nortonownersclub.org/

https://www.accessnorton.com/NortonCommando/gearbox-identification.18335/

https://www.accessnorton.com/NortonCommando/commando-1974-gearbox.17821/

- edit: tranny is short for transmission, apparently often used, even alone in ads for norton boxes, or bikes in general

acotrel · Mar 21, 2018

The AMC box which is used in a Commando has a longer main shaft (about 6mm) to accommodate the diaphragm clutch.

84ok · Mar 21, 2018

will that mainshaft fit an atlas or other boxes? along with the other commando internals, then bolt on to a commando?

baz · Mar 21, 2018

84ok said:
will that mainshaft fit an atlas or other boxes, along with the other commando internals, then bolt on to a commando?

Someone else should chime in with the differences in earlier gearboxes ,
I really can't remember what the differences are?
But in answer to your question about the atlas gearbox yes you can fit a commando main shaft into the atlas gearbox, all i actually changed was the main shaft it still retains the atlas gears etc have done this myself in the past , I hope this helps

84ok · Mar 21, 2018

baz said:
Someone else should chime in with the differences in earlier gearboxes ,
I really can't remember what the differences are?
But in answer to your question about the atlas gearbox yes you can fit a commando main shaft into the atlas gearbox, all i actually changed was the main shaft it still retains the atlas gears etc have done this myself in the past , I hope this helps

absolutely! tx!! exactly what i'm after, key info new to me that tells me what i can make work with commando,

prior to this, my searches for g/b parts was limited or 68-74 specific,

acotrel · Mar 21, 2018

I'm pretty sure any AMC box will fit into a commando and the internals are all similar, except for the mainshaft. On my bike, I use a TTI gearbox with a single row primary chain with a Manx clutch. The TTI is intended to be used with the diaphragm clutch, so the mainshaft is too long. I get around it by using Jawa Speedway engine sprockets floating on a splined carrier I had manufactured. It depends on what you use the bike for - I would not do that on a road bike.

acotrel · Mar 21, 2018

Many of the pre-1960 Matchless and AJS had AMC boxes which can be used in a commando, if you change the mainshaft or use an early clutch .. If you don't change the mainshaft in the earlier box and use the diaphragm clutch, there is an alignment problem of about 6mm.

triumph2 · Mar 21, 2018

acotrel said:
Many of the pre-1960 Matchless and AJS had AMC boxes which can be used in a commando, if you change the mainshaft or use an early clutch .. If you don't change the mainshaft in the earlier box and use the diaphragm clutch, there is an alignment problem of about 6mm.

The main gearbox casting used in AJS and Matchless gearboxes had the mounting lugs in a different location to the Norton boxes.

Ron L · Mar 21, 2018

The Atlas and other slimline featherbed gearbox cases are wider at the top boss for the fixing bolt. The Commando uses a spacer here while the Atlas does not. You could mill the top bolt boss on an Atlas case to match the Commando and use the Commando spacer. I don't think you can fit the Atlas case in the Commando cradle without milling it.

The Atlas and G15/N15/P11 outer gearbox covers are threaded to accept the clutch cable adjuster and is located further rearward than the Commando cover. All inner gearbox covers are the same for Atlas, Commando, N15/P11.

84ok · Mar 21, 2018

from above link
http://preservationcycle.com/index....-norton-commando-gearbox&catid=86&Itemid=1739

The casing on the Commando was also reduced at the upper mounting bosses to make installation easier. It was thinned and a separate spacer was fitted between the engine mounting cradle and the box. Leaving this out can distort the cradle, so be careful!

In 1968, at number 128646, the high gear pair was modified for strength and durability, and these gears must be a matched set. The tooth profile and number was altered and they will not mesh properly if they are mixed. This also raised the ratio of first, second and third gears. Later on the 850 Commando, the second gear pair was altered starting at number 306591 to enable the bike to pass tougher noise regulations. The test involved passing a noise meter in second gear at a certain speed, so the gearing was altered to allow this to happen at lower revs. Clever those Brits.

lcrken · Mar 21, 2018

Also some more info on the same question here:

https://www.accessnorton.com/NortonCommando/amc-gearbox.3955/

Ken

lcrken · Mar 21, 2018

And more info on gear ratios here, including a table of them that I posted:

https://www.accessnorton.com/NortonCommando/commando-gear-teeth-thread.18349/page-4

Ken

hobot · Mar 21, 2018

Rest assured Atlas shell is identical to Commando except the Atlas shell does not force ya to fart with the stupid thick wedge spacer, just fit gearbox align holes, shove in bolt nip up done. Atlas shells are about 1/2 cheaper last time I shopped 15 yr ago. I've a Qualfe shell that Icrken Canaga did a bolt hole weld up repair for me. I like its beefy looks. Did not use as eventually afforded a New Zealand ITT 4 spd.

So far no cost effective way to restore wallowed out AMC bearing bores so eventually will run out. About 15 yr ago called world wide looking for Commando gb to learn the major shops each had a big pile of cases that by now likely scraped out. The only place I know that still has piles of good Commando and Atlas shells, plus other Commando items, is Baxters Cycles.

marinatlas · Mar 22, 2018

Do not forget also the inner cover is different in some manner of fixing the kick spring , (between Cdo and early Atlas ), as the Cdo one is fixed to a "stud" and the earlier one have a peg going into a hole in the inner case , the springs are different , the late model is far better , more positive return action , and less possibility of going off .......

oldmikew · Mar 22, 2018

marinatlas said:
Do not forget also the inner cover is different in some manner of fixing the kick spring , (between Cdo and early Atlas ), as the Cdo one is fixed to a "stud" and the earlier one have a peg going into a hole in the inner case , the springs are different , the late model is far better , more positive return action , and less possibility of going off .......

Yes , and the AMC box fitted to the Model 50 had a shorter mainshaft than its contempories

pierodn · Mar 23, 2018

a

triumph2 said:
The main gearbox casting used in AJS and Matchless gearboxes had the mounting lugs in a different location to the Norton boxes.

and the lugs tunnel (not for Atlas) are thin instead commando one so you must drill to enlarge.

84ok · Mar 23, 2018

overhaul pdfs & info buried in other threads

http://www.archives.jampot.dk/Technical/Transmission/AMC/AMC_Gearbox_Stripdown_and_Rebuild__(Classic_Mechanics_1987).pdf

http://www.archives.jampot.dk/Technical/Transmission/AMC/AMC_gearbox_Overhaul__Roy_Oliver.pdf

http://www.archives.jampot.dk/Technical/Transmission/AMC/

84ok · Mar 23, 2018

hobot said:
Atlas shell is identical to Commando except the Atlas shell does not force ya to fart with the stupid thick wedge spacer, just fit gearbox align holes, shove in bolt nip up done. Atlas shells are about 1/2 cheaper last time I shopped 15 yr ago.

related post from another thread
https://www.accessnorton.com/NortonCommando/gearbox-identification.18335/page-2#post-272972

The main difference I could detect from N to NA is the kick start shaft return spring and length of the bush in the intermediate cover are different.
The cases DID grow beefier as time went on. With at least 3 grades within the commando series alone.
Different/improve hardening of the gears (AH) within commando .
I own 15 AMC gearboxes on the shelf and another half dozen in bikes through MKIII 75. I am missing the 50's versions but have at least one "N" and several "NA".

Personally I would never use an early gearset or case in one of my commandos. 73 & 74 are the best, 75 is too specialized for general commando use. IMO

new topic related to thread
https://www.accessnorton.com/Norton...ce-bulletin-mixing-gears-or-made-pairs.24865/

84ok · Mar 23, 2018

marinatlas said:
Do not forget also the inner cover is different in some manner of fixing the kick spring , (between Cdo and early Atlas ), as the Cdo one is fixed to a "stud" and the earlier one have a peg going into a hole in the inner case , the springs are different , the late model is far better , more positive return action , and less possibility of going off .......

http://preservationcycle.com/index....-norton-commando-gearbox&catid=86&Itemid=1739

The kickstart spring design was changed in 1962 (64 for Norton)

hobot · Mar 23, 2018

In my newbie ignorance after world wide vendor with decades seasoned experts via expensive phone call pestering for replacement of Commando AMC gb shell i got good 1/2 price Altas used shell that all the '72 Cdo parts fit in finer than cdo numbered parts. Solved it for me to move on to other issues. I just want to be a pilot so your call how to get there too. I had so many issues with original AMC Cdo gbox I ran out of gaskets so just splaped together with goop to find out that solved the lay shaft shim issue to boot.