Dynamo belt tension

[MG]

Hi to all!

I just returned from a little trip on the A10, had to return back home after I heard a very weird, flapping noise coming from the timing side. It disappeared as suddenly as it came, and I got no more charge, so my first assumption was a broken dynamo belt.
So off with the timing cover and bingo, there it was, disintegrated to it's basic atomic elements  

It's been in there for 800miles now, last time I checked tension was 400 miles ago since I had the timing cover off to fettle with the oil pump. I have adjusted it according to SRM's instructions, saying you should be able to twist it by 90° easily (i.e. without applying great force), holding the belt between two fingers. This appeared a bit loose to me, but as it wouldn't have enought play to touch anywhere, I thought I'd better do as instructed (for once in my lifetime, ha!).

So my question is: Any similar experiences out there? How do you set those things up?

Electrical system is bog standard 6V with mechanical regulator and 35W headlamp, and I'm doing 90% daylight riding with only the pilot and rear light on. So the belt shouldn't feel too stressed in there. The dynamo is turning nicely and freely when spun by hand. I will try to motor it, to make sure it is okay.

P.S.: Since there has been some discussion about it recently: The felt washer behind the large sprocket is still in excellent nick after 800miles, no signs of wear or damage whatsoever.

Cheers, Markus - off to the shed again, the large belt drive pinion needs two threaded holes for ease of removal next time!!!

[a10 gf]

Have you tried super-glue  ?

Maybe send a PM to our resident SRM member, and ask him to post some comment or hints.

[bikerbob]

Hi there I think it unlikely that the belt will have snapped but are the pulleys inline or maybe too much end float which would allow the belt to rub against the side of the pulley and the over 800miles it maybe rode over the pulley and came off one pulley and then came apart.

[MG]

Thanks for the comments, chaps, I shall try the super glue if I can find all the lost teeth  

There's no end float and pulleys are nicely in line, that's been the first things I have checked when fitting the belt. Regarding the noise it made it has been mangled through the pulleys quite a few times to make it look like that.

[alanp]

MG there's info on the forum on the subject of dynamo belt failure. Try searching for 'dynamo belt' on the home forum section. Mine lost most of its teeth but didn't break. My guess is that yours lost teeth and the teeth went under the belt around a pulley and over tensioned it and mayhem ensued. I've gone to a 15mm wide belt and all is well so far.
Alan

[MG]

Hi Alan!
Thanks for the info, looks like it happened to some of us already, while others last for years. I'll try to contact SRM tomorrow and send them a link to the ongoing discussion here. Tomorrow's one of those fancy religious holidays here (don't ask me which one), I assume it is a normal working day in Blightey though?

I think this is the link you were referring to, Alan? I've even posted there, but forgot about it, senile is the word...

http://www.a7a10.net/forum/index.php/topic,3748.0.html

The 15mm belt kit lloks brilliant, but honestly I'm not too keen on spending money on another two sets. I might try another SRM belt with a bit more tension than recommended in the instructions to avoid teeth chafing somewhere and see how that works.
I was wondering what happened to a belt that was bent during transport, with some of those internal wires breaking? Could be an issue with pre-mature failure.

Cheers, Markus

[muskrat]

G'day Marcus,
                   exact same thing happened to me last weekend. Teeth missing, snapped belt. About the same miles too, and that's the second one on the '51. I'm using Gates belts on it, and the red Synchroflex on the cafe (lost teeth on that one too). And guess where I ran out of battery (electronic ignition), right at the spot I had my tumble last month on the same bike !!
 Pulley's line up, belt runs to the inside of one and outside of other but no marks on side of belt. Dynamo runs free, just a tad of end float on the idler shaft (no felt or cork, no oil in compartment). I may have an overcharging problem in that the amp gauge always reads 4-6 amps at revs, drops back to 0 at slow speed and -3 at idle. Might be a problem with the DVR2. That's all I can think of for my problem.
Cheers

[trevinoz]

My chains don't do that!   

  Trev.

[MG]

Ha, I'm not alone, thanks Musky!

right at the spot I had my tumble last month on the same bike !!

spooookyyyy  


Trev, good point, I am already strongly thinking about fixing the loose rivets on my old chain sprocket and putting the chain back on.
If it's no up to the occasional 7000rpm blasts, then it's not for me  

[Brian]

I'm another one who has stuck with the chain. I thought about going to a belt but have heard too many problems.

[wilko]

I'm surprised no one has a 1/4 inch chain and sprocket conversion on the market like Matchies use as standard on their generator drives.

[bsa-bill]

Just to be awkward (who me never), I'm happy with the belt, to be honest while I do less miles than many of you I've had more trouble with the chain and it can do a lot more damage in there when it goes.
I do set it a bit tighter than SRM suggest, 90 deg twist OK but not easily, should remember that even with steel cords it will stretch a bit from new.
And as I've mentioned before due to a befuddlement (senior moment) I managed to get the dynamo section of the timing case fill with oil - belt never slipped, dynamo charged throughout.

btw  - befuddlement - much to my surprise is a genuine word the - spell checker passed it first time of asking

[jjbsa]

hi, I'm quite concerned  to read about these problems with timing belt dynamo drives, as about 200 miles ago I fitted one to my bike, which I converted to 12 V electrics at the same time.    (The belt drive was fitted in good part because it spends the dynamo faster).  I suspected that there might be the odd problem with this type of drive because  before deciding which kit to buy,I noticed that Hawker Electrical now offer their kit with a pair of toothed belts and also Dynamo Regulators Ltd stress that their belt is wider than some.  For this reason I bought a belt kit from Dynamo Regulators Ltd. and can only report that so far it is okay.  My belief is that these belts should be tensioned quite tight and that the "Bend through 90°" test should require a modicum of  effort.    However, I must admit I can't help but feel that I would like to have a rather more objective measure of tension, such as X amount of effort to deflect the belt at its midpoint by so many millimetres.    It  would be helpful to get a feel for how common the problems with these kits really are.  I don't really want to go back to a chain drive, because should it fail it will make quite a mess. the thing that concerns me about the belt drives is the question about will they cope with the loading when one changes up with the motor is about 7000 rpm?  I have wondered about trying to squeeze a little metal to metal clutch in there, like they have on Magdynos, but right now that is project number 349.

[A10Boy]

Bad luck Markus. I fitted one of the Dynamo Regulators, 15mm jobbies a few weeks ago, so far so good. I'm still running 6volts and rarely venture out at night. [Well you wouldn't would you], so I imagine it's not under much load.
It occured to me while I was fitting it that it's like a car engine cam belt in miniature. I've fitted several of those over the years and used that experience to judge the tension on the belt, it should twist 45 degrees fairly easily, 90 with a bit of effort, and you should still be able to feel some play / flex on its long length, just.

[MG]

Gary from SRM just responded, here's the chain of emails:


Hello Markus,
 
it is not a common problem, as i rarely sell spare belts.
 
Looking at your belt it seems very dry? It seems failure was more than likely over tensioned, remember always check belt tension after engine is at running temperate, also these belts can be run in oil and grease, and the timing cover of an A10 is a very hot place , so best to put some grease in the cover to help keep it cooler and some lube.
I did the same on my A10 years ago with a clutch belt drive with similar type drive belt , i run it dry with tension on the tight side, at high temperature the belt failed, similar to yours in appearance, i fitted a new belt with a slacker tension and run in oil, i never had a problem after that.
 
Regards Gary

Hello Gary!
 
Thanks for your reply! I haven?t checked tension with the engine hot, but when cold set it up as instructed (belt easily twisted by 90°). I shall try to adjust with engine at operating temp. If you don?t midn, I will post your response on the forum?

Hello Markus,
 
yes no problem, it is a consideration that heat expansion affects the dynamo pulleys and engine casings, so always best check belt tension when engine is hot, same goes for clutch belt drives.
 
Regards Gary