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Jez Nemeth

Well Known and Active Website User
VOC Member
Bit of advice sought here. Putting together a Comet, slight mods, but nothing much more than standard really 8:1 piston, ported, carb. Just rebuilt an Atlas gearbox for it and now puzzling over primary drive.

Box is set with adjusters as advised in that excellent article by Conrad Osborne, edited by David Dunfrey "fitting an AMC/Norton Gearbox to a Comet".

We have a complete Commando clutch for Triplex chain + mainshaft (fitted to box), Vincent Comet main engine sprocket -single chain, springs and gubbins as per standard.

Choices are as follows as to what happens next:
  • Fit a Norton beltdrive clutch basket system, fettling an alloy pulley for the Vincent mainshaft at the front, AT10 belt - can just about get a 1.6 tooth ratio, near standard. Problem is that with this there's no cushdrive in either the Commando clutch centre or rear hub, not really enough 'give' if at all in the system -from what I understand belts are tighter than a chain too, short lived gearbox is what I'm sensing, as nice as the Newbie's Clutches are, rather not stretch that far if possible.
  • Option two, Ditch the commando clutch, get an old AMC one with cush drive rubbers and run a standard single primary chain.
  • or thirdly, one I'm leaning towards financially -forget belt. Use Commando clutch, fit a twin sprocket set up on the crank end with triplex chain -done.
Any experience, advice, advisories, warnings, thoughts, all appreciated.
 

vibrac

Well Known and Active Website User
VOC Member
Dont worry about primary ratios there is leeway on the back sprocket choice
Dont understand your worries about belt drive my Newby's (I have two on Vin singles)belts will turn 90 degrees mid run and one has no adjustment at all I just buy a new belt one each year or so.
I was going to use a twin sprocket to drive a duplex chain to reach the albion clutch on my Flash but Im glad I ditched the chain the newby on the Albion is smooth and it allows the albion to actually change gear
 

Jez Nemeth

Well Known and Active Website User
VOC Member
Good advice -even talked to Bob a time ago -it was just the most expensive of the three options I rekkoned -but if its the best option in the scenario, then bite the bullet and I'll order a set from him -they do seem to be the best way to go for simplicity and maintenance free running.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
Just like to know that my thinking was not too far off centre with the other options. Had folx employed any of those methods with a Norton box and did they work? -Be going the Bob Newbie route, appreciate the very good advice Vibrac, I'll start saving the pennies, but as said, just for knowing...
 
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greg brillus

Well Known and Active Website User
VOC Member
1.6:1 Ratio is for the twins, singles are 1.8:1 might be over geared to buggery's if you use the twin ratio. i'm just assembling a Comet 600 with AMC box and Newby belt primary, need to have the gearbox hard up against the engine to get any slack in the belt. Like you say, no cush drive, and i still worry about the non sealed hub bearing in the Newby clutch center as to how long it will last in a road bike without stripping yearly and relubricating the bearing assembly. If I twist this belt to 90 degrees, it would fall off in service, more like 45 at most. Belts need the same adjustment as per a chain, not too loose and not too tight.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
Thanks for that -1.8 sounds more workable! No cush rubbers in a Newbie Clutch I'm assuming then? Those belts, particularly the newer AT10's steel reinforced would have less 'give' than a chain I'd have though... 90/45 twist -is that how the tension is checked? -or am I having a dull moment here...
 
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greg brillus

Well Known and Active Website User
VOC Member
Some think that a belt has some "Give" in it to soften the drive, but that is not the case. There is no cush center in the Newby clutch center, they are a fabulous assembly, although primarily for racing. I just don't believe they are entirely maintenance free, as far as the center bearing goes.
 

Jez Nemeth

Well Known and Active Website User
VOC Member
Some think that a belt has some "Give" in it to soften the drive, but that is not the case. There is no cush center in the Newby clutch center, they are a fabulous assembly, although primarily for racing. I just don't believe they are entirely maintenance free, as far as the center bearing goes.
Curious to measure that centre bearing against a sealed Commando belt drive system bearing ...just a hunch Greg....

So, if there's no "give', and it works regardless, not destroying boxes before their due dates, could I just buy a Norton Commando Belt toothed clutch basket (and sealed bearing), use the clutch plates/diaphram I have, work out the right length belt -in 8mm or AT10, profile/pitch, and fettle a £30 correct ratio 1.8 pulley for front crankshaft fitting?
Save a bundle if that's the case...and get pretty close to a spot 1.8 ratio
 
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Jez Nemeth

Well Known and Active Website User
VOC Member
Like yer thinking...Strangely, the twin ESA -when I had one lying around, and curiosity grabs you, as it does - well, it fitted cleanly under the cover -the chain I don't know. But my good friend mr Dremmel tells me it would fit fine...
 

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