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C: Clutch Comet Primary Drive Q's?


Jez Nemeth

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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

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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

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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

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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

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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

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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

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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

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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

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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...
 

Chris Launders

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Cheapest method and possibly best, get a steel front pulley and machine/weld to the comet sprocket centre then alloy clutch basket, so you will still have the cush drive and a pocket full of cash. you don't run a belt tighter than a chain (see above) and certainly won't destroy a Norton box. I've been running a twin motor/ belt drive/Norton box over 15 years.
 

Jez Nemeth

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Often the sweet scent of low price is outlasted by the bitter taste of low quality, but that sounds pretty realistic Chris..be some measuring involved. So welding to the ESA sleeve then, or turning down the Vincent sprocket -welding a steel pulley to it -using the ESA + spring set up with a belt? That's kindof ideal. Got to be careful, need to be running a 32 toothed steel pulley on the shaft -be tight. Any adverse issues with the belt bunching under gear changes? F08466E4-97E9-4D33-A85A-D02EDDBB5910.jpeg...
 
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Chris Launders

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No No No, I don't have a Comet but you should be able to work out a way of turning the sprocket down and the pulley out so you can weld them together and keep the ESA., in effect the inner of the sprocket with the outer of the pulley.
 

Jez Nemeth

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Chris, my curiosity and bank balance thank you for this...will be looking into the parts tomorrow -RGM Norton and a few others are good sources for the bits. Must admit, was curious about doing something of this ilk -glad to hear it works and well -sounds best of both worlds.27400
 
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oexing

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Best option is NOT to install the Vincent ESA and you will never have any problem there. What that crap device really does is braking even triplex chains - as is well known.
Where do you think will shocks develop, from the rear wheel, from the primary drive ?? The crankshaft is quite heavy and will not induce any big shocks into the drive within one cycle. Chain drives are not as rigid as shaft drives like on Guzzis or BMWs. So , as Neville Higgins has found out, that non-elastic shock absorber slams onto both limits when accelerating or braking the engine, no damping at all due to its shapes. I bet nobody has ever snapped a belt in a non ESA setup, or a decent chain in no-ESA bike.

Vic
 

davidd

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Jez,

You have confused me with so many choices!

Greg rightly points out that the single primary ratio is higher than the twin and with the 36T Newby engine pulley and the 68T clutch the primary ratio is very close at 1.89. Like Tim, I prefer the quality and reliability of the Newby. It is difficult for the other options to match the overall performance of the Newby. The extra cost should pale when compared to the performance and reliability of a Newby.

These belts have no give in them. They are the same as timing belts and you cannot have give in a timing belt. I do think that racing may prove to be somewhat easier on the primary than stop and go driving. But, on the other side is the excellent clutch. I believe it is a better shock absorber and it is able to be slipped often without any damage.

Finally, the Newby fits inside the Comet primary with some mods to the inside of the primary. That saves a little cash and protects the whole primary.

David
 

Chris Launders

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I must admit mine has no has no cush drive anywhere and consequently is a bit harsh, I have a picture of what I consider an ideal one , although I am considering changing my Manx back wheel for one with a cush drive in it.
 

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Jez Nemeth

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David, You put it succinctly -and yes, indeed I am similarly a little confused -its why felt the need to post initially, but less so now. Belt drive would seem the way to progress, unless the conversation heads towards a "Chain vs Belt" -for and against conversation then we're into another ball game...Newby does seem to be a fully sorted well tested system -highly regarded by everybody, and yes quality comes at a price...choices!
 
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Jez Nemeth

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One other consideration that may ultimately swing it -Norton Commando clutch basket fits, with very little room but it does. If running 58 tooth clutch, AT10 Belt, the front pulley diameter for 1.8 ratio = 32 teeth (32.2) + Flange is 4" 3/8 total diameter, fits with a bit of dremmeling, but tight...represented here with correct sized card disk. The Newby I'm assuming is a better fit and possibly an easier clutch? (Been watching Comet Mongrel avidly on how to make a Norton clutch easier on the lever). Great advice, and considered responses truly appreciated -learnt a lot in a few short hours.

So it seems to come down to either a home grown belt solution, or the Newby system. That's a big step forward from where the thinking was.27402
 
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Chris Launders

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You could easily go down on the engine pulley size, there are a vast range of gearbox sprockets for the Norton box to take it back up and you're nowhere near the Hp/torque figures of a Commando.
 

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