Gearbox Identification

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Stephen Hill

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I picked up a gearbox that externally looks like a Commando box. The case is stamped N5176. Looking at Bacon's Norton Twin restoration guide, N in an ENGINE number could mean 1958. Elsewhere, he says that Norton gearbox cases are identified with an N or NA.
Any ideas what I have? And how much of this will fit a Commando???

Stephen Hill
 
AMC gearboxes don't have year letters, like you say.
N or NA is Norton dommie, M is Matchless (the housing mounting lugs are different).

Pre Commando, the early boxes had less strong gears.
And the mainshaft will fit a single chain AMC clutch, not the Commando clutch.
The case was strengthened for the Commando at some point too.

So, short answer is it won't really suit a Commando at all.
With a change of internals, it could be made to work.
Thats why it was cheap ??
Cheers !
 
How were the internals made stronger in the commando box ? The earlier AMC boxes have been run behind supercharged Vincent twins. I think the only time there is a problem is if a heap of revs is used in getting the bike off the mark, and the primary drive ratio is too low - then the main shaft might bend.
 
The root thickness of the gear teeth was increased.
You can't mix gears of the AMC and AMC Mk2 gearboxes.
Thats why they always advise to only ever change gear PAIRS....

This wasn't for the Commando though, this was sometime in the early 1960s.
For the SS dommies, perhaps. Or as a result of (?).

The gearbox was the archilles heel of the JPN race Nortons in the 1970s,
if you wade through the race reports.
Outrigger bearings solved it a little in the later ones.
And quaife boxes etc had the strengthening ribs incoporated around the box.
Nortons were always playing catchup with the strength of gearbox components... ?
 
Outer cover of the pre Commando gearbox has the clutch cable attachment further to the rear and the hole is threaded. Something I noticed when rebuilding a '61 ES2.
 
Your ES2 would have had a 1/4" drive chain sprocket. ?

Where somewhere later, the sprocket became for a 3/8" chain,
as the Commando also used.
 
Rohan said:
Your ES2 would have had a 1/4" drive chain sprocket. ?

Where somewhere later, the sprocket became for a 3/8" chain,
as the Commando also used.
Click to expand...

My point was the location of the clutch cable insertion point on pre Commando outer covers as an identifier. I believe up to the Atlas, the outer cover was the same '57 onward as that was the first year of the AMC box.
 
Different subject.
Did your ES2 gearbox have the 1/4" sprocket/chain size ?
 
Yes, my ES2 has a 1/4" wide chain.

Gearbox Identification
 
Another 'subtlety' is the Commando gearbox casing upper mount is machined narrower on the primary side to enable fitting in the Commando cradle - hence the need for a spacer when fitting the upper mounting bolt.
 
Stephen Hill said:
Does anybody have a link to a detailed evolution of the AMC box?
Click to expand...

Hasn't been done yet, that I have noted anyway.
Unles you count the above here...

The NOC has a page or 2 on the various gears and shafts that were fitted to Norton boxes over the years.
 
illf8ed said:
My point was the location of the clutch cable insertion point on pre Commando outer covers as an identifier. .
Click to expand...

It could be commented that Norton boxes had that threaded adjuster on the gearbox cover on the clutch cable,
going back prewar on the early AMC, laydown, upright, and dolls head/WD boxes.

The adjuster was trapped/incorporated in the clutch cable - which meant it was difficult to make and slow to change a cable.
But the adjuster couldn't get lost ....

Not relevant to Commando's, which had the adjustment for the clutch cable at your fingertips, right at the lever.

BTW, Commando boxes are stamped on the top mount with the same 6 digit number as the engine,
so you know the approx details of any Commando box you come across.
 
Rohan said:
The root thickness of the gear teeth was increased.
You can't mix gears of the AMC and AMC Mk2 gearboxes.
Thats why they always advise to only ever change gear PAIRS....quote]
Gidday Rohan. hope u r well. Mate, I do have a very keen interest in this subject and am always learning. so could you please enlighten me further on this.

What do you mean by root thickness ?.
Do you mean root fillet instead?.

increasing the root fillet would indeed add to the tooth ability to handle contact stress .

The danger point still remains though, especially in a case hardened gear.
So accompanying this should have been other tooth modifications as well.

Were these other modification applied to the tooth as well?.
I am a bit confused as to what you mean here mate. Your explanation will be of enormous help in my understanding.

Mixing MK1 & MK2 gear pairs..

does this have anything to do with the modifications made to the Ratio of the second gear pair to comply with noise emissions control. this would prohibit interchangeability of the second gear pair only depending on method used..
The centre distance is constant. Tooth profile modifications alone may not necessarily affect interchangeability. It depends on the method used to modify the teeth.
Have I got this wrong?.

I have a previous post called bad teeth. I reckon that this modified tooth profile will fit straight in to the existing space with considerable advantages.. mesh perfectly with the existing gear. Totally different tooth shape to the original. Does not require the replacement of the other gear at all. U can change only one. (assuming both gears are new). No changes are required to the geometry of the other gear.. what does change is the ratio of the gear PAIR.

Am I correct in this assumption ?.

So if essential dimensions are the same, and the action is conjugate, what prohibits interchangeabilty?. There must have been a change in essential dimensions. Do you know what they were.?.

Changing gears in pairs. yes, it should be done.

The main reason to do this is because of the likelyhood of the existing gear having wear and surface damage. the wear may contribute to rough and noisy running, but more important is the increase in stress and resulting damage to the new gear, or even failure of the Pair of gears. .

Taken to extremes, tooth breakage will occur. Sooner rather than later. Where have I got this wrong mate?.

I am not trying to wind you up. I have a passionate interest in these boxes. Any information increasing my knowledge is greatly appreciated. I am fair dinkum here.

If this is off topic , would you please start another thread. best wishes Aussie bradley.
Click to expand...
 
B.Rad said:
Have I got this wrong?.
Click to expand...

Yes.
Early and later AMC gears CANNOT/SHOULD NOT be mixed, they are not the same tooth form.

Gear PAIRS are OK to use togther.
Commando gears can even be used back into quite early gearboxes.
As long as that gear pairing is adhered to.

Ask the new phone support guy at AN if you want any more details,
they have all the eng drawings and blueprints.... ?
 
Norton boxes stamped N#### were built from 1957 - 1962.
Norton boxes stamped NA#### were built from 1963 - 1968.
Commando boxes had the engine number stamped on them starting in 1968.
My Mercury gearbox is stamped with the engine number followed by an N. Go figure.

According to Roy Bacon, the AMC 1 box was built from 1956-59.
The AMC 2 box was build from 1960 to 1973. The internal gearbox ratios changed on these dates.
Note that the N or NA stamping has little to do with the AMC 1 or 2 stamping.

In Norton Twins Restoration, Bacon identifies a number of changes to the box, but the information does not seem exhaustive.
Mick Hemmings in this article also identifies a number of changes: http://www.archives.jampot.dk/Technical ... 987%29.pdf
Putting the two souces together would probably capture most of the changes.

I plan to use the N#### gearset in a Commando. I may use the N#### shell as well. I keep hearing the gears and the shell are too weak. Can somebody please point me to where these weaknesses are documented, and when or how they were rectified? As far as I can find out, the early gears and shell are no weaker than those used in the first couple of years of Commandos.

Stephen Hill
 
The tooth form was altered in the Mk2 AMC box.
If you have the earlier box, they are less robust.
Whether this will be a problem only you will find out.
You also will need a Commando mainshaft, or the Commando clutch won't locate.

The shells were thickened and strengthened, quite a number of times.
The 850 gearbox shell is thicker than earlier, when you examine it.
"Thicker' being a relative term, the housing has to fit into a defined space,
and the gears need to fit inside. The increases were very modest.

It has oft been discussed that a few kilos of extra thickness in Nortons castings could have improved reliability, considerably.
But that sums up the entire brit motorcycle business, ultimately. ?
If only....
 
Rohan said:
B.Rad said:
Have I got this wrong?.
Click to expand...

Yes.
Early and later AMC gears CANNOT/SHOULD NOT be mixed, they are not the same tooth form.

Gear PAIRS are OK to use togther.
Commando gears can even be used back into quite early gearboxes.
As long as that gear pairing is adhered to.

Ask the new phone support guy at AN if you want any more details,
they have all the eng drawings and blueprints.... ?
Click to expand...

Gidday Rohan. Thanks for your prompt reply. Exactly why can they not be interchanged?.
and what do you mean by tooth form. I think you mean profile and pressure angle.. There may have been a change in pressure angle but I dont think so. I will research and find out.

Tooth form is a meaningless term when referring to interchangeability. all gears of same tooth size but different tooth numbers have a different profile. look at 17 T and a 50T profile. they will still have conjugate action but very very different looking profiles.
So to support your claim you must give the specific reasons leading to the conclusion that they are not interchangeable.

Was it a change in pressure angle. And when. I wiill check this out.

If any 2 gears have the same centre distance, DP, pressure angle, and same porportions regarding addendum, working depth and so on they will interchange. gee, they sometimes even have different addendums and still have conjugate action.

tooth shape has very little to do with interchangeability.

All AMC boxes after 1950's are 10 DP 20 degrees pressure angle. I have not comfirmed this yet.Some pairs have long addendums and these will not interchange with standard addendum's. .

Some very very early boxes may have 14 1/2 degree pressure angle. it is now almost obselete. this makes a difference. But I reckon after about 1940 or even 1950 all AMC boxes run 20 degrees pressure angle. all twins will be 20 degrees so any twin box gear will interchange.

so it depends on what u mean by early. They never did change the centre distance and that is a telling point.
if there is no change in pressure angle, the gears will interchange if proportions are the same. Again the definition of interchange becomes important.

mate you still have not rebutted my claim that the main reason not to interchange a pair is because of the consequences of wear. technically an old and new gear will mesh and run.
but for reasons previously described the mixing of old and new is all about the consequences of wear, not interchangeability. As to gear pairs are ok to use together, technically can I make at home a 12 tooth pinion of correct proportions, and run it with a new AMC 28 T gear ?. the 12T replaces a14T.

of course I can. the new 12T and standard 28T are now a pair.

Mate, gearing is an incredibly complicated subject. it is very very difficult to have a discussion about the technical aspects in one or 2 paragraphs here. Volumes have been written on gear design.

By trying to reduce discussion to a short format, it is so easy to have the subject taken out of context.

And we still have not discussed your claim about " root thickness" being the main reason for more strength. and durability is just as important as strength. It is important not to give did\sinformation to interested lay persons.

In any discussion on gearing, it is absolutly essential to use the same precise terms used in the gear engineering field. comparing apples to apples. terms like long addendum, drop tooth, pressure angles, base circle, strength and durability ,tooth profile shift are essential to any discussion about gearing.

You cannot have a simple debate about technical aspects of gearing. So much is inter related.

So the debate about interchangeability comes down to one question .

"Did AMC ever run 14 1/2 degree pressure angles". This should be very easy to establish.. Then the discussion can continue once this is established for certain.

I will start a new thread on this very subject as it is too easy to hijack this one.
I do thank you for your reply and look forward to further discussion in another thread. Best wishes Aussie bradley
 
hobot said:
[video]https://www.youtube.com/watch?v=WYcqJ5HdxA4[/video]
Click to expand...

YES, they do indeed. hobot thank you for supporting my point that gearing is a very complex subject. well illustrated.

to go to extremes, there are eliptical gears driving a spur pinion AT VARIABLE SPEED, used to be used in very old large clocks.

But a point to remember with these unusual gears like this. they do mesh and turn. However, the load carrying capacity is very low indeed. not meant for big HP. a novelty item really.

Thanks again mate Aussie bradley
 
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