The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: MG on 14.08. 2011 17:38
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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 *eek*
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!!!
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Have you tried super-glue *smile* ?
Maybe send a PM to our resident SRM member, and ask him to post some comment or hints.
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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.
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Thanks for the comments, chaps, I shall try the super glue if I can find all the lost teeth *lol*
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.
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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
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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 (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
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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
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My chains don't do that! *smile*
Trev.
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Ha, I'm not alone, thanks Musky!
right at the spot I had my tumble last month on the same bike !!
spooookyyyy *eek*
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 ;)
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I'm another one who has stuck with the chain. I thought about going to a belt but have heard too many problems.
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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.
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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 *yeah*
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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.
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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.
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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
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Since I don't feel too confident about running the belt in either oil or grease, and since I'm positively sure it was not over-tensioned, and since some others run those things for 15000+ miles without problems (hi groily *wave*), I wanted to get at the bottom of this, so today got Conti's design tool and fed the geometry and power data into it to see whether the belt is basically up to the intended purpose.
So for those interested, that's the calcs and results:
belt type: Conti AT5 GenIII, 420mm length
pulley1: driving pulley (intermediate pinion at half engine speed), 46T
pulley2: driven pulley, 17T
The calculations are based on a power of 100Watt (0.1kW) on the driven pinion (assuming 60Watt electrical power output and 40% power loss in the dynamo, which I think is quite reasonable for a DC brush-operated design) at roughly 1900 generator rpm (this being the design rpm stated in the Lucas service sheet), thus resulting in the highest driving torque over the operating rpm range.
The results show a maximum transferable power of 0.52kW on the driven pulley, so we are facing a safety factor of 5.24 here. The belts are designed to work in temperatures up to 100°C, reduction of maximum power above 50°C is not taken into account in these calculations, but with a safety factor of more than 5 there is plenty of room there.
So the good news is that these belts should be more than up to the task and failure actually is very unlikely.
What is interesting though is the required pre-tension force in the belt, which is 18.5N (about 4.1pounds) in each span of the belt. This is quite some tension, imagine an 8.2 pound weight hanging on the belt, and the "easy 90° twisting-thing" from the mounting instructions misses the point here imo.
So I'm led to believe that my belt failed because it wasn't tensioned sufficiently, I shall give it another try with a new one and this time rather trust my own judgement than the instructions (let's face it, probably t'was my fault this time) ;)
Cheers, Markus
edit: Lacking equipment to properly measure belt deflection or frequency of oscillation, this could be a neat idea to get the pre-tension about right: Hang an 8.4pound weight on the belt using two discs similar to the pulleys in diameter and twist the belt by 90° to get a feeling for the necessary force, and then apply same to the mounted belt. *idea*
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Brilliant analytical work Markus, as ever!
But I'm embarrassed to say mine is indeed going strong on at least 15000 miles. Probably rather more, but speedometer repairs have never been a priority for me.
Not ridden it at your or Musky's 7000 rpm though, it has to be said, just normal boring backroad 55-65mph cruising with blasts up to 75 or so. It's only a cooking iron engine after all and it's done who knows how many miles. I am running an extra tooth over standard at the gearbox to keep things sweet on main roads, but that makes no odds to the dynamo. Had a look at the belt a few weeks back when doing some mag swapping. First time I've had the cover off in ages and the belt tension seemed the same as when I put it there. Those with long memories will remember a few years back I had nowt but trouble with the pulleys, but having resolved that by re-using the original drive sprocket's steel centre in a re-machined SRM pulley, no problems.
I've been darn lucky, this very tatty bike's bullet-proof - or has benefited from some sorcerer's sprinkling of magic dust. It can't run for ever, natch, but it continues to surprise me.
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Hi Bill
Good to hear of your 15,000 mile and going strong modified SRM belt drive. At the Loreley International I sold a Belt drive kit to one chap, whose dynamo chain broke the next day. And a Danish guy next door to our tent replaced his dynamo chain on arrival. There may well have been more. Then at our Hampshire BSA camp a member missed the run due to noise from timing cover which proved due to the eccentric sprocket issue which is very familiar.
Interesting guide calculation from Markus via Mulco. The Gen III belt is good for 100 C continuous so de-rating from 70 C is in order. So even more safety factor to allow for shock loads through the dynamo. I think it important to note that over-tensioning is warned against strongly by those who should know. Better a small amount of slack rather than too much tension. And the tension does increase markedly with the engine hot. Erring on the tight side when setting cold will lead to excessive strain on the belt. It certainly would be useful to come up with a better measure of tension that does not rely on expensively derived 'feel' as the belt is twisted.
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Thanks for the comments, manormike. I shall adjust at operating temp to be on the safe side.
I agree, proper measurement of the belt tension would be at order. Anyone got a good (i.e. cheap) source for those small frequency counters? ;)
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A forked rod slipped over the belt, with a force balance at a set length to allow torque measurement at a given twist. Might work to take away the subjectivity in setting tension.
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yeah, but then there is the problem of translating the required pre-tension force (or oscillation frequency for that matter) into the appropriate twisting torque, i.e. some sort of calibration will be required.
I have found a post on another forum, where one of the guys wrote a LabView program to measure the oscillation frequency of car engine timing belts, using a laptop and microphone, just like those small hand-held devices do it. Unfortunately the link is broken. *sad*
Anyone here good at Fourier analysis and software programming? ;)
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Markus, et al,
Not that I am anyone to challenge the belt manufacturer's or your (Markus's) mechanical engineering calcs, but I have a question. In the power calculating program, the number of teeth in mesh on the driven pulley is given as seven. The drawing would appear to support this, however, it seems to me that only half that many could be working a any given time, as the top run of the belt is in tension while the bottom is trying uselessly to push. Then, I wonder if more than even the first couple of meshed teeth are truly working, the work having been mostly done before getting to, say, the third meshed tooth. If correct, would this change the results for maximum power that the belt could tranfer?
On the question of oil or grease in the case, i can't see how it would hurt, as the belt can't possibly be depending on static friction from the face of the teeth to avoid slipping around the pulley. At the same time I don't see how it would help.
Richaed L.
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Hello Richard!
You are right about the bottom of the belt being more or less uselessly "pushing" the pulley, hence the need for pre-tension in the belt to keep as many teeth as possible in mesh and avoid slipping of the belt. The higher the load on the belt, the higher the pre-tension (and width of belt). These effects are taken into consideration in the calculations, should be at least, that is the problem with such design tools, you can't be sure what it is doing in fact.
Gates' tool (called design flex pro iirc) for example also offers the possibility to distinguish between constant and periodic/intermittent loads, thus reducing the maximum transferrable power by 50-100%.
That is also the main concern I have about grease or oil in there, reducing friction in critical situations, like insufficient tension plus a torque impulse or resonance effects.