belt drive 2nd failure

Keith1069 · May 22, 2015

Thanks for that Dero........took a closer look at the pulleys and the drive one is horrible, badly worn, squarish profile to the teeth (instead of a nice radius). With the tight wrap around that, the belt cannot have been having a good time with the teeth digging in every revolution. What surprised me about these belts is that while on paper they have a tensile strength and torque/speed beyond what the engine puts out thats in the belt itself. The teeth are only moulded in place with no steel re-inforcement. I'd not realised that till the first one broke. These pics show the wear. I'm going with a new pulley and Contitech belt for now....I did say earlier that there was no reinforcement in the teeth but a close look shows some material there but most of the tooth is rubber and only a few strands of 'cord' barely embedded in the tooth. Conti diagrams show only tension cords in the flat belt and nothing in the teeth so is it really only the shear strength of the teeth that resists failure?

Pics re-added.......

swooshdave · May 22, 2015

I vote for new pulley too. :mrgreen:

Hobot · May 22, 2015

In above photo note the sloped uneven teeth wear which implies the clutch basket or crank shaft not stable so more belt tension/load on outside. Also note the rough surface and under cut wear which a rubber belt can not do w/o grit involved. I really abused Ms Peel sealed belt drive to wipe sneers off sport bikers reactions before intense joy rides yet only saw smoothly polished off anodizing and even teeth wear except inside broken out teeth notches left by processing crank nut through teeth a few loud times before thrown out the way. Would of re-used Peel well worn belt drive but feared it not up to blown big block power and is not factory numbers so not for Trixie Combat.

Only photo I can find so far for how evenly polished off Peel belt teeth were near end of her life, here about 500 miles after the over rev event that seized up with a slight clinking sound coasting a few mph into shed. Thinking the worse started tear down with primary to find was only a side plate screw vibed out to jam lightly between plate and case so put back in for another 1500 mile of so depressing normal Combat power I gave up on her.

Onder · May 22, 2015

Pre MkIII have no cush. You would have to speak with Madass and get his cush rear.
Id not worry about failure unless it was unplanned. In other words if you have a interference belt drive cam in head like a Honda Civic you dont change it when it looks bad you change before it does on mfg's schedule.

Keith1069 · May 23, 2015

Thanks for that Dave, I moved the pic to the folder. Yes its a mess and seems to be more worn on inside edge (case side retainer is more worn than outer since I added a second adjuster). It always used to run off the outer a little and settle with 25% belt off the pulley when turned by hand. I may have overdone pulling the box round a bit. On the oil front I did find the tiniest nick in the seal lip, just felt with a finger. That and all the sump oil may have done it. The belt is a Contitech and the original a Gates. The Gates had more abuse and lasted 3 x longer. Still can't understand why the Conti' still drove stripped of teeth and covered in oil when the Gates wouldn't even get going dry and that still had 1/3 of its teeth left. On the wear side of things the neutral colour Brecoflex belts are claimed not to dig in like the conventional black ones.

worntorn · May 23, 2015

Onder said:
Pre MkIII have no cush. You would have to speak with Madass and get his cush rear.
Id not worry about failure unless it was unplanned. In other words if you have a interference belt drive cam in head like a Honda Civic you dont change it when it looks bad you change before it does on mfg's schedule.

I thought this too and was corrected on another thread (MK3 changes) It is fair to say that the 1971- 1974 pre MK3 hubs have a sort of a cush, though it is a pretty wimpy looking affair and I'm not sure how much cush it actually offers. From my reading, pre 1971 bikes do not have any cush in the rear hub.

Glen

swooshdave · May 23, 2015

Do you have dual adjusters on the gearbox?

B+Bogus · May 23, 2015

swooshdave said:
If you are wet sumping it shouldn't be getting into the primary case. What is your breather situation?

I don't think the oil is the primary cause of the failure. Are you SURE the belt isn't too tight?

I was thinking the same thing with regard to the breather. I've had issues with the crank seal in the past, and although ( as it turned out :roll: ) somewhat contentiously I believe the standard steel-cased seal to be a weakness area.
Both bikes I've used them on have let oil past, and my Combat was forcing oil out of the primary until I replaced the seal with a 100% rubberised one - similar to the ones supplied by Steve Maney.
It also had a PCV fitted, so it clearly doesn't take much.

Another possible leak path is the primary mounting bolts.

The belts I run are from RGM and are oil resistant AT10 Synchroflex - definitely not rubber, which may or may not be oil resistant?
I have my suspicions, but no first-hand experience of them.

http://www.rgmnorton.co.uk/shop/search. ... earch.y=16

pete.v · May 23, 2015

B+Bogus said:
The belts I run are from RGM and are oil resistant AT10 Synchroflex - definitely not rubber, which may or may not be oil resistant?
I have my suspicions, but no first-hand experience of them.

http://www.rgmnorton.co.uk/shop/search. ... earch.y=16

Just a side note, to run an A10 belt you will need A10 hubs. I think the A10 system is the key attribute for the RGM unit.

Onder · May 23, 2015

Recently I was crying about oil leaking from the crankcase into the primary. I was using the metal type seal. Even tried Jim's idea of using epoxy on the edges. No joy despite several tries and careful installation.
Went to the all rubber type and completely dry now.

Yes, there is a cush in the later 750 and 850 pre MkIII rear hubs. It works when the buffers are new I suppose better than nothing but nothing is what
you will have in short order. Putting the wheel back with new buffers is tough too. Doubt they last more than a few thousand miles. As soon as they
get a little use you get slop in the drive line. Make do short term thinking.

Proper cush drive would seem to be worth it if you drive hard or use the bike on rough roads.

Hobot · May 24, 2015

Space craft looking solution Ludwig mean while best I can come up with is slicing cushions out between piles and sidewalls.

Onder · May 24, 2015

Ludwig, how do you change out a flat on the side of the road? I guess you demount the whole wheel-drum
together?
About what you have to do it if the standard buffers are new .

marinatlas · May 24, 2015

Hi Jan, so clever system ......!! must do that .....!

Hobot · May 24, 2015

hehe clever Ludwig upgrade that adds spun and unsprung mass, to humorously nic pic.
Belts transmit more shock loads than chains references say d/t the chain many micro oil layers compared to continuous non forgiving belt fibers so only belt slack flop and its small rubber layers engaged in teeth absorbing some. There are other innate cushions in Commando besides the rear hub. oil layers in gear box, isolastics inline of tire pulsed drive and tire rubber patch too. Peel may need a chain tensioner d/t her 2 inch longer shocks angling the swing arm down more but Water Buffalo hub has very robust permanent cushion. There are racers who get away w/o cushions but they do not spend much time in lugging slow pulsing states.

B+Bogus · May 24, 2015

I'd never given the cush drive any thought with regard to premature failure until I changed the back tyre yesterday - 2 of the 'rebound' rubbers had bounded off somewhere else altogether, and the remaining one was looking pretty sorry, so it's definitely worth regularly replacing them or following Ludwig's properly engineered solution... Or Madass' 'proper job' cush hub, which is looking rather attractive at the moment.

I suppose 31 years is a lot to expect from those little rubber blocks, but it's certainly made me think about including them as a consumable in a regular maintenance schedule.

Keith - I hope you've got a way forwards with your belt drive - I seem to recall it being mentioned somewhere... :wink:

Brooking 850 · May 25, 2015

Ludwig, very clever, what is the wafer thin piece for the back lash made of?

Any mechanical noise once the springs loose tension and do you need to use 3 x preload bolts with a tapered tube to mount the wheel onto the drum brake stubs?
Regards Mike

Brooking 850 · May 25, 2015

Thanks Ludwig, I tried using 2 x equal size pieces of pink shutex rubber on the race bike, as I have a small sheet of it and the right thickness when two pieces are put in that hub space just makes it easy to get the tangs in with a firm push, even though it is supposed to be high impact, they tore up quite quickly.
Racing yesterday here in New Zealand , another competitor on a Briggo, it is a similar frame to a Norton featherbed but modified to accept a Jawa 500 speedway type motor.He stripped 2 x belt drives and threw away a chain , no cush drive seemed to be the main issue as well as being a big single. He is working on that !!!

Regards Mike

Keith1069 · May 26, 2015

Keith - I hope you've got a way forwards with your belt drive - I seem to recall it being mentioned somewhere... :wink:

Ha ha and yes!!! A minor hi-jack is no problem as long as it leads to something useful :lol: Found the tiniest nick on the seal lip, very small and hardly noticeable without a magnifier but probably enough with more than tickover revs and a fullish sump to do the business. I always seal the three inner primary screws with sealant

and have recently blocked the inner ends with epoxy. Now waiting on Norvil to mail me the new pulley and belt.

Hobot · May 26, 2015

If ya tend to deal with inner primary now or in future I suggest replacing fumble bolts with red loctited permanent studs. Save thread wear tear and and no weeps with chain case off and slips on held aligned too.

Keith1069 · Jun 1, 2015

Fitted new front pulley and belt. Norvil decided their advertised list prices were out of date so added a bit more for luck! That and a 300% markup on the belt + snail mail at next day prices meant I only got it back on the road for the weekend. Turns out the belt is HTC brand, unknown to me (same as failed part) but can't find any info on them other than $18 from UK supplier now I know what it is, but $63 from Norvil :x Seems it was worth changing the pulley as a 110 mile run didn't show any rubber dust from the new belt and the rubber housed seal kept things dry in there. It was an easy push fit so it has been fitted with 'Superglue'. Yes its going to be a pain to remove and cleanup but here's hoping it'll last.

belt drive 2nd failure

Similar threads