What type of clutch is this ?

The belt shown is an HTD type tooth profile. The clutch type is commando diaphragm. The center diaphragm is probably aftermarket due to non standard components. Likely a commando gearbox main shaft....

Hi Mike,

The clutch content I expect is pure Norton - however you clearly have a belt conversion - a good thing.

I expect its either a RGM or Norvil - I've fitted a few RGM and the teeth look different, so expect its an Norvil - others can confirm.

Regards - Paul.

Just picked this thread up Mike it is a commando clutch. In order to protect the longevity of the gearbox, they should have fitted a commando rear wheel and cush drive, as a belt has no cush drive properties which protects the gearbox bearings and gears especially when changing gear, 

People often claim that belts are too stiff to provide shock absorber properties. But the belt manufacturers claim their shock absorber properties to be a principal advantage over chains. No fabric (not even Kevlar) is as stiff as the same weight of steel, and I suspect that belts aren't much heavier than chains, and the belt teeth are rubber anyway. Do owners of belt drive bikes Dommies actually find that their drive is problematic?

It's almost certainly a Norvil belt drive. The front sprocket looks like the one on my Commando and they sell a kit that comes with a Commando clutch that is modified to fit the Dominator gearbox mainshaft. I think the benefits of a belt drive outweigh the loss of the cush drive in the clutch. As David says, the belts are claimed to have an element of shock absorbing in them.

The two important things to note are - make sure the sprockets are in line and don't run the belt too tight.

Ian

hello this is the commando  diaphragm   clutch  and they need special tools to remove  the outer clutch mechanism ,  Bob Newby clutches  are Better  in many ways         yours  anna j 

Hi Mike and all

I agree with all the above.

Would like to stress what Anna drew attention to. Do NOT attempt to dismantle / assemble this style of clutch without the correct Commando clutch diaphragm spring compressor tool. It's very dangerous and care needs to be made re-seating the diaphragm spring on assembly. Some aftermarket ones are not as well machined as those fitted to original Commandos. Pay attention to the groove for the huge diaphragm spring circlip .

Interested in the comments re; no cush-drive and introducing a rear wheel with cush-drive.

A friend into "parading" laps [read ex - racers having fun, legally!!] they "lost" [read trashed] 2 gearboxes in one weekend. 

So [from high-mileage riders] are we to understand that for normal road-work the designs are sound and the belt itself has sufficient "give" to protect the gearbox? 

I would be very interested to hear your [road] experiences / mileages etc. 

Regards

Tim S

Guess what the only Commando's that failed to get home from Austria this year were using, I'll stick with the chain. 

Mike, Tim and others. I certainly do NOT agree with all the above.

AJD seems a proponent of BN coil spring clutches,

Some have reservations, considering many are Brits:

https://www.accessnorton.com/NortonCommando/norton-vs-bob-newby-clutch.21901/

Seems using the right tool would go without saying.....?

Mikes clutch is commando diaphragm "style" and yet may not actually have one norton (manufactured) part. barnett friction and clutch plates? QPD diaphragm-after all it is not OEM in appearance?

RGM and others use AT-10 type belts so those are out. This one is easily identified as HTD style. Norvil being only one maker among many.

Gearbox longevity VS cush drive VS clutch/chain mass

While I had to take BDM insults for almost 20 years, He did seem to agree with some of my concepts about commando primary drive attributes. 

The triples chain and very heavy clutch basket were problematic when not set up to perfection.

My observation of open chains on race bikes show the chain whipping about in a crazy fashion at a variety of rpms. All this whipping about is causing the crazing of the gear faces. with a heavy commando clutch/chain it is like beating the gear faces with a sledge hammer.

I own 23 AMC gearboxes, many in commandos and featherbeds and also am no stranger to RGM and Norvil belt drives. Talking to a highly successful norton racer, I conclude that regardless of the kevlar (HTD) or steel (AT-10) cords having no cush that primary benefit is the lightness of the belt and basket and my preference for the solid fiber friction plates as the weight/mass is MUCH less.

I have noted the lighter atlas chain/clutches have much less gear damage than with the heavy stock commando triplex chain/clutch.

A noted local commando racer early in his racer day was drag racing, sprinting for you . He would be rebuilding his gearbox after every weekend of racing. He switched to a norvil belt drive and would then go for the whole season only rebuilding in the off season. This was in 1988 and at that time I installed a street norvil belt on my overhauled/reconditioned combat.

Personally I tell local club members to put a belt drive if it is a bike you will use and "drive".... show bikes don't need it. The heavy chain whip is eliminated and makes the bike much more pleasant to ride and even more importantly it reduces gearbox damage.

Dave... Do you go so far as to advise feathered owners to fit a (costly) Commando rear hub to recover the cushion drive? Your post suggests to me it is not necessary.

I am only passing on my experiences and what I have learned and from other credible folks.

IIRC from way back when the cush inserts seemed to be a bit rubbery, they might have actually done something. Todays rock hard inserts don't inspire confidence they actually do much "cushing" at all. I myself would not persue adding a cush drive commando rear wheel to any of my 4 featherbeds. I have or will be using one norvil HTD and one AT10 RGM commando style clutch on 2 of them. If I can get some time, one may get to try a 920 with Drouin supercharger for a while for sprinting/drag racing....

cheers

Putting a cush drive in the rear hub has got nothing to do with protecting the gearbox from the engine. If you remove the cush drive from the clutch and the rear hub there is nothing to absorb the energy created in the chain. The energy created when you take up the drive is like the rear sprocket being hit with a hammer. This energy created on the hub travels through through the rear sprocket to the chain onto the gearbox sprocket which puts a strain on the gearbox bearings. If used like this it will wear the sprockets and the chain, and eventually affect the gearbox. The cush drive is not meant to be a work of art it is designed to absorb the energy created when you let the clutch out.