Triumph T140 Bonneville

▲ Here's what can happen when a Triumph T140 primary drive belt gives up the ghost. It happened on a sixty mile trip from London to Brighton. First there was a soft ping. Then another. And then no drive at all. No roadside fix was possible, and the bike was recovered. The entire clutch, alternator and engine sprocket) had to come off. And then the fun began...

▲ The internal wires were entangled everywhere, and fragments of red plastic/fibre littered the housing. Helluva mess, but nothing else was damaged. This one had covered maybe a thousand miles. Or less.

▲ We've fitted another Hayward rubber band (spare one). So far, the T140 is still running. In theory, you can run these belts wet or dry. But if you run dry, the Hayward kit doesn't supply a sealed clutch bearing, so you'll have to factor in a lot of maintenance with an oil can.

Note that if you run a belt dry on a T140, you'll need an oil seal  on the end of the crank where it exits into the primary chain case, and you'll need to glue-up the three oil-return holes (also inside the primary chain case). You could then refit the primary cover and splash a little oil in the primary case manually (maybe an eighth of a pint or so), and regularly check the level. That will separate engine oil from the oil lubricating the primary case/clutch bearing. But then you've got to revise your breathing (which, on a Triumph T140 or T120, is pulsed through the drive side main bearing and into the primary case, and then out through a breather hose). Problems. We've got a breather pipe connected to a stub screwed into the top-dead-centre locating hole behind the barrels. It works, but not well. And it occasionally squirts a little oil through the breath pipe that exits at the rear of the pipe. We'll be returning the set-up to standard asap.

The problem

Triplex primary chains on British bikes are heavy and sap power, and they can wreck your engine when they break. That's the orthodoxy. So after many years of dithering, we finally decided to fit a belt drive to one of our T140s and see if they were all they're cracked up to be.

Our system was designed and sold by Tony Hayward. Tony's been in the business since Noah floated his boat, and over the years we've got to know him and have always considered him a straight-shooter. And we still do.

We had an older kit that Tony doesn't sell anymore (a different pitch or something; possibly 14mm). The engine pulley is cast steel. The clutch pulley is aluminium alloy.

Tony helped us upgrade this kit with a new clutch and we installed it in the usual way. We also fitted Tony's "red belt" which, as we understood it, was top of the range. However, within less than a thousand miles it failed and left us jammed up for hours on the A23 London - Brighton road awaiting a recovery truck.

▲ One of Sump's long-suffering T140s. Trusty. Hardworking. And indefatigable—until we fitted a belt drive.

The Solution

Not so much a solution this time as some observations. We brought the bike home and kicked it a few times and went to bed. The following morning, it became clear that it wasn't simply that the belt had snapped. The internal wires had sprung loose and had wrapped around the engine sprocket, the alternator and the clutch drum.

Additionally, the plastic/fibre "meat" of the belt had disintegrated and had deposited the pieces everywhere. A total primary strip and clean out was needed.

One of our concerns was that the stresses had damaged a bearing, but we couldn't find any evidence of that. None of the clutch plates were damaged, and the alternator was fine. So we phoned Tony to ask what the hell had happened to cause the problem.

He asked if we had fitted the kit properly, which we thought we had. There are, after all, only so many ways that it can be fitted. Actually, just one. And yes, it seemed to be lined up properly, etc. But if it wasn't, there's no possible adjustment.

We were offered a replacement belt, gratis, but we declined and put it down to bad luck. Instead, we fitted another belt that we had kicking around. That item was quite old, but unused. However we wanted to try it as an experiment. Why? Because Hayward doesn't know what the shelf life is. But he recommends replacing them after a handful of years.

We might have upgraded to his current (closer pitch) design. But we'd just fitted a new clutch that wouldn't fit the new system, and we wanted to get some value out of it. So we opted for trying an older (standard) belt as opposed to the top-of-the-range belt that had failed us.

The second rubber band went on without trouble. We looked for any way that we could fit it wrong, but the options were few. Actually, they were zero. It's now been running for maybe 500 miles, mostly in London traffic, so plenty of stop-start riding. Plenty of short journeys too. And plenty of heat down there in the primary case.

After we fitted it, we called Tony again. He said that our peculiar problem had never happened before, certainly not with a relatively new belt. Indeed, he spoke of customers running the same belt after many tens of thousands of miles and a decade or more of riding. Ours, therefore, must have been faulty (we've since been sent details of an identical failure).

However, ignorant as we are of primary transmission design and manufacture, it's difficult to see what fault could have been there that wasn't apparent when we fitted it. We hadn't damaged anything during assembly. It's a standard T140 motorcycle. We followed the instructions (fit and forget). And the high-tech band broke long before its time.

▲ When the red belt failed (main image, top of the page), we fitted an older Hayward item. It's still running on our Triumph T140. But we're grimly awaiting the end.

The Conclusion

When this one fails or dies of old age, we're returning to a triplex chain. We've since learned that these belts can fail "hydraulically". What happens, apparently, is that if you run one within an oiled-primary case, the oil is pumped up twixt the plastic/rubber/nylon teeth and the pulley. That adds stress. Additionally, the pulleys, being metal (steel and aluminium) expand. It was a fairly hot day when ours snapped, and we'd been in heavy traffic weaving in and out with plenty of torquey moves.

Is it possible therefore that the combination of these factors conspired to snap that high-tech primary "chain"? We think so, but we're not sure. Either way, we're pretty much done with this system. After fitting this one, there was no obvious improvement in acceleration, noise levels, smoothness, etc. Maybe that was hoping too much. But we expected some kind of improvement. However, all we got was failure.

And consider this, after years of running chains, we've never had a failure, and have never met anyone who has. Yes, a snapped chain can wreck an engine. But you will pretty much always get some warning that things aren't right. Moreover, we think that primary chains have more latitude, and they'll expand together with the sprockets.

But it's your call.

Other riders, we know, swear by belt drives and have racked up plenty of satisfied miles. But some of those guys are running dry clutches, thereby precluding the "hydraulic" problem. And if you're running a T140 dry, you're going to have to regularly strip the primary to manually lubricate the clutch bearings.

We don't for a second believe that Hayward doesn't have genuine faith in his product. But his faith isn't matched by our experience. If you're looking to go this route, we suggest you speak to him, and other suppliers, and ask about our experience. We might just have been unlucky. And we might be unlucky again if and when this belt goes west. But we won't be unlucky a third time. We'll be letting the chain take the strain.

Sump visitor feedback

Hi Sump

I recently had a bit of an ‘event’ with my 1978 T140V which had me researching the above mentioned belt drives. I see you also have had an incident with one of the ‘heavy duty’ belts so though I would share my experience.

I fitted my first Hayward belt drive back in Oct 1995 after reading good reviews and reaching the point where the plates on my triplex chain clutch were wearing out. The original belt was great. It fitted exactly as Tony Hayward's instruction sheet said it would. I had to remove the rubber off the primary chain tensioner, but other than that it went on no problem.

Fast forward to Jan 2012. I have, in the interim, moved to Australia, bringing all my bikes over with me, and after covering several thousand miles I checked the clutch. A couple of the friction plates were giving up, so, being as Tony doesn't seem to do any online stuff and calling from Australia is not easy with the time difference, nor cheap, I got my 80-year old mum to talk to Tony and send new plates and also a new belt, as the old one had been on for a long time.

When she came over (bringing the items with her), I fitted the belt and plates and went on my merry way—until today, Oct 2015, when I was left stranded in the middle of nowhere with a loss of drive.

I plan to put the old belt back on, seeing as I have new plates in the clutch. I would contact Tony as I said, but he makes it quite hard from here. So I will see how the old standard non-heavy duty belt wears, and get it all back together.

Just thought I would let you know, as in your story you say Tony claims yours was a bit of a one off. Well he was wrong!!

I attach a photo of the belt taken just before I stripped the whole thing apart to clear away all the bits of red rubber and strands of steel belt!

Regards

Mark Stidever

Queensland, Australia.

Editor's note 1

We had a number of questions regarding this issue and asked Mark for clarification. Below is his response:

In answer to your questions, I have tried to scan Tony’s fitting instructions, which I received with my belt drive kit way back when. I have attempted to lighten/darken the scanned sheet, which is very faded having spent 20 odd years tucked into my workshop manual! I hope you can read it OK. I will type out as much as I can read from the paper copy here in front of me.

So yes, I do still have the primary chain tensioner installed. And as per his instructions, the rubber was burnt off, and the face of the blade polished so as not to damage the belt.
I run the belt in oil. I thought about running it dry, but reading in various forums I see that that has heating problems and issues with lube for the clutch bearing rollers.

Also, with the engine breathing through the primary chaincase via the little holes through the crankcase, I could never see how to block those off and allow the engine to breathe from somewhere else. I did try once. I blocked the holes with tiny screws and modified the exhaust rocker inspection cover to allow the engine to breathe that way. Wasn’t really successful. Didn’t want to go drilling cooling holes in the primary cover so that remains complete. I use thinner oil in the primary rather than the heavier oil I have in the engine.

Editor's note 2

The T140 engine breathes through the drive-side engine bearing into the chaincase. As standard, there's no oil seal there. Therefore, oil is also fed into the primary chaincase through that same bearing. The three tiny holes in the bottom of the primary chaincase are intended to return the oil to the crankcase and maintain a suitable level. You can retrofit an oil seal against the drive-side main bearing. But the three return holes must be blocked. Araldite will do it. If a drive-side oil seal isn't fitted, there's no point in using thinner oil in the primary chain case. It will simply mix with the engine oil.

On one of our own T140s, we've got an oil seal on the drive-side main bearing, and the three holes are blocked. But we still run the primary case in a little oil via the top inspection cap. We've never heard of using the primary chain tensioner with a belt.
 

The instructions read:
1. Do all you can to get front pulley to fit well inwards – like removing any engine sprocket spacers – which some engines used.
 

2. You must use your standard rotor spacer at back of rotor as normal. The back face of rotor should clear the front face of the front pulley by 1 to 5 thou.
 

3. Make sure that the front face of the clutch drum is well clear of the l/hand gear change spindle. You may have to grind a little off the spindle rod if it fouls the front face of the clutch drum.
 

4. Belt tension at hot running temp. After 15 or so miles should be 3/16” total slack (free play) and not 3/8” free play as per primary chain. At running temp (HOT) the max free play is 6mm and minimum free play of belt is 3mm:
 

5. If the belt is too tight for your particular engine I can supply a smaller clutch drum.
If tension is too slack you’ll have to use your standard slipper blade – you must burn/bake off the rubber off the slipper and polish the part that would rub on the belt.
 

Any problems get back to me.
P.S do not damage/bash the teeth on the pulleys.

Hope that is of some use to you. The belt drive I had fitted originally covered thousands of miles, I would check the tension when servicing but didn’t have to adjust at all, the slipper just helped achieve the correct tension in the first place. As I said, I plan to put the first belt back in. I only changed it for the new ‘heavy duty’ one as I thought it would be better/safer than one that had been used for 20 odd years! Found out yesterday that is not the case!!
 

Andrew Kilty's feedback...

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