Norton Gearbox

Wonder if someone can help me with this?

Can second gear mainshaft AHA or AHB be used with AH layshaft second gear?
Is that a viable match?
What's the difference between AHA and AHB?

Cheers, George.
BC, Canada.

scotnort75 said:

Can second gear mainshaft AHA or AHB be used with AH layshaft second gear?
Is that a viable match?

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Not AHB.

scotnort75 said:

What's the difference between AHA and AHB?

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They're a different ratio (18/24 and 18/23 'AHB' 850 Mk1A-on) although both main shaft 2nd gears are 18T, there's a dimensional difference so don't attempt to mix the two types.

Thank you L.A.B.

Of course if you had a copy of the Norton Owners Club Commando Service Notes book you could of read on page 6 and I quote....' From Engine No. 306591 a new pair of 2nd gears were added 064639 and 064640 fully interchangable with previous pairs 040418 and 040019. On NO account mix the gears, pairs only. The reason for the change ? The factory said ' to provide a more graduated set of ratios ' actually it was to up the ratios therefore lower the revs in 2nd gear to pass noise restrictions'. I heard it was to pass USA noise level restrictions wher of course most bikes were sold generating the most cash flow to keep them afloat..after having totally failed to introduce the new models we were told to be produced when the Atlas Mk3 or Commando as they later named the lumps whiuch were intended as a 2 year stop gap bike to bring in cash while new models were designed developed and introduced.....Yess of course we laughed.....we knew all about the problems AMC were having with the new 800cc double overhead cam motor being developed......No point in drinking with a friend every Saturday night who was serving his apprenticeships at AMC if you didnt hear the latest cock up tales......
If you do not have a copy of said notes I would suggest you obtain a copy and read them. For example it actually gives, unlike the manuals as I remember them, apart from the late Mk3 manuals, the torque value to use when tightening up the rear wheel....80 ft lb. We simply used a long spanner and stood on it thereby stretching the threads......It also tells about the rear wheel spacer that had a material change to ensure rear wheels no longer came loose in use .......etc

Going back a zillion years I remember later Commando gears being stamped AH and with a line machined into the face of the engaging dogs.
Also and this really is strtching the memory banks one gear was increased by one tooth and the other retained the same number of teeth but the pitch diameter of the toothform changed and the difference in pitch diameter was not really noticable to the eye but it was when you shoved two rollers between the teeth on each side of the gear and measured across the rollers which if i remember correctly is how one checked the gears to the drawing. Something tells me the rollers were shown on the drawing as something like 0.24 inch diameter but I am lucky if I can find my way home on my own these days...... Does anyone have the drawing? I know someone who will have but I aint going to drag himout of the machine shop simply to look up the drawing and the other person, now retired, who I phoned a few minutes ago to ask said he had not bothered to copy them before he left.... yes of course I gave him a bollocking for not doing so.
I SUSPECT that for the new gears being manufactured since NVT went base over apex or arse over tit they will be stamped up to distinguish between the early and late gearsets Ie AHa for the early version gearset ???? and AHB for the late version gearset ????? That seems logical but I learnt decades ago to NEVER assume anything so can someone confirm or correct PLEASE.

J. M. Leadbeater said:

Of course if you had a copy of the Norton Owners Club Commando Service Notes book you could of read on page 6 and I quote....' From Engine No. 306591 a new pair of 2nd gears were added 064639 and 064640 fully interchangable with previous pairs 040418 and 040019. On NO account mix the gears, pairs only........

I SUSPECT that for the new gears being manufactured since NVT went base over apex or arse over tit they will be stamped up to distinguish between the early and late gearsets Ie AHa for the early version gearset ???? and AHB for the late version gearset ????? That seems logical but I learnt decades ago to NEVER assume anything so can someone confirm or correct PLEASE.

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Although, of course :roll: the NOC Service notes doesn't actually mention how to identify the individual gears so anyone seeing AH, AHA, or AHB on odd gears would be left none the wiser seeing as both mainshaft gears are 18T after all, you're not entirely sure yourself, but seem to have been marked AHB before they went bust!

J. M. Leadbeater said:

The reason for the change ? The factory said ' to provide a more graduated set of ratios ' actually it was to up the ratios therefore lower the revs in 2nd gear to pass noise restrictions'. I heard it was to pass USA noise level restrictions wher of course most bikes were sold generating the most cash flow to keep them afloat.

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Strange, that, as the new "Low noise emission" 850 Mk1A & 2A models were sold on the European market and the US kept the noisier non-A Mk1 & 2 models, although both Mk2 and Mk2A models got the higher ratio 2nd gear.

The "newer gears" can be identified by grooves in the face of the dogs. I just swapped a "new" set in my '75 for an older pair and I like the "old" standard ratio combiation better.

Deets55 said:

The "newer gears" can be identified by grooves in the face of the dogs.

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Indeed, the AHB gears had the groove but again the NOC Service Notes make no mention of it.

The answer is that the gears marked AHA are the early Dommy / early Commando gears and the ones marked AHB are the later 820 2nd gears 064639 and 064640 which have to be used as a pair and should not be mixed with the earlier gears.
As for the NOC Commando Service Notes not mentioning things they dont even mention the stress raiser they left during manufacturing inside the crank so cranks would break more easily but I do note that bronze plate clutch users are advised to use Castrolite in their chan case. Not that Castrolite, a straight 10-40 oil, as advised for chain case use on BSA A65s incidentally, is avalable these days but either Silkolene or Morris oils flog, or did flog when I enquired, in quart pots a straight 20 oil that would be far more suitable than the oils so many exspurts advise.....oils with friction inhibitors for example which are the last thing required when the friction dependant clutch is already, and here I am being VERY polite, prone (hah hah)to clutch slip problems due to oil....as the Commando Service notes mention in passing....... I note they mention that bronze clutches should be taken apart and the black gunge that forms on the friction interfaces causing clutch drag problems (the result ofheat generated by clutch slip burning off the oil on the friction interfaces) should be removed by cleaning in petrol...gosh reminds me of my youth when our little gang had a pot of petrol used specifically for washing oil off of our clutch plates at very regular intervals to cure our clutch slip problems which were probably the result of using the threottle fully most of the time OR overfilling our chain cases as my Norton Dommy manuals state on the problems page!!!! Ok delete 'most' and insert 'everywhere possible' !! Amazing how so many actually survived.....not that all did but they were the lucky ones the unlucky ones were often in a wheel chair or brain dead for life..... They did not sign part of the old A20 DEATH HILL for no reason!! (Or Gorse Hill as it is now named with ' FORMALLY DEATH HILL written beneath) Bet the local residents objected to their postal address..they should go live in Pratts Bottom a few miles away !!

J. M. Leadbeater said:

The answer is that the gears marked AHA are the early Dommy / early Commando gears and the ones marked AHB are the later 820 2nd gears 064639 and 064640 which have to be used as a pair and should not be mixed with the earlier gears.

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I thought we had already ascertained that long ago with regard to the 2nd gear pair. :roll:

Commando gears were (and still are) generally marked AH (including the original 2nd gear pair) except layshaft 4th (marked with what is either a '6' or a '9' but AH now).

J. M. Leadbeater said:

As for the NOC Commando Service Notes not mentioning things they dont even mention the stress raiser they left during manufacturing inside the crank so cranks would break more easily but I do note that bronze plate clutch users are advised to use Castrolite in their chan case...............

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Do you think perhaps we could go a week or two (or even longer) without you continually attempting to steer subjects off-topic and onto Commando clutches?