Dynamo belt knacked

[Greybeard]

After fitting my new battery I checked the ammeter and saw no movement 😕

Today I had the chance to get the bike up on the hoist and had a look at the dynamo. I took out the spark plugs, put the bike in gear and rotated the back wheel to check that the dynamo was turning. I noticed that the dynamo rotation was irregular! A screwdriver applied to the armature shaft screw allowed the dynamo to easily turn.
Next step was to take the timing side cover off. I found that the dynamo belt was loose and stripped of teeth. The case was liberally covered in dust. When the belt was removed I could see that the toothed pulley on the dynamo shaft had almost no teeth left!

I want to use the bike tomorrow so I've put the spare belt on that I bought with the original order. I'll order another belt and a new dynamo pulley.

The belt kit, from Dynamo Regulators, was installed in 2012.

[dave55]

Hello, how many miles do you reckon you have done since it was fitted ? that does not look good though,methinks i would have put chain back on. 
 

[RDfella]

That's a small dynamo pulley. If it's steel, no worries, but if it's aluminium probably only good for 5,000 miles or so. The belt on my M21V2 (15mm wide) had done thousands with no sign of belt or pulley wear (they were steel - now alloy with the change to electric start).

[Greybeard]

I don't know how many miles I've done since I fitted the belt conversion 10 years ago. I'm going to guess at 1k miles a year so 10k miles.
I went for a drive after fitting the spare belt. The ammeter is doing what it should be doing so the knackered pulley is working at the moment. I've sent DR a message asking if I can buy the dynamo pulley and another spare belt. The kits are now sold by Steve McFarlane so I may need to contact him.
There was an incident  😕 while I was out which I'll write up in the appropriate department.

[muskrat]

G'day GB.
I had trouble with my belts stripping until I put a good lump of grease in the compartment.
You've done well at 10,000 miles and 10 years dry!
Cheers

[Brian]

I have done 22,000 miles on my Dynamo Regulaters belt drive and the pulleys show no sign of wear at all. I have replaced the belt once, at about 15k I think it was and I think that was my own fault. I had to take the gen off so removed the belt but I didnt mark the direction of rotation of the belt before I removed it. when I put it back together the belt self destructed almost immediately so if you remove your belt mark the direction of travel and put it back on the same way.

[bsa-bill]

the belt looks a tad slack GB, which might be due to small pulley wear or tensions being lost at some point and belts slipping which would account for the wear on the pulley.

[Greybeard]

the belt looks a tad slack GB, which might be due to small pulley wear or tensions being lost at some point and belts slipping which would account for the wear on the pulley.

The belt was extremely slack when I opened the case but then it had lost all its teeth 😁

[Black Sheep]

I'm reminded of the advice given by one of the overland Land Rover gurus when asked about modifications are needed for an expedition. Leave it standard - that way you can always get spare parts.
Our A10 has passed the 100,000 miles now. No dynamo chain problems in that time.

[Swarfcut]

 Its not the teeth that transmit the power, it is the tension on the belt. A slack belt will shear the teeth off. Why the belt slackened off could be due to the soft dynamo sprocket, or simply movement of the dynamo. I mark my dynamo/crankcase and it is a simple matter then to check the marks stay in line. Like all belts, they need checking from time to time, tho' it is tempting to fit and forget.

 Swarfy.

[Greybeard]

Our A10 has passed the 100,000 miles now. No dynamo chain problems in that time.

The main reason I fitted the belt was to quieten the hen🐔gin

[muskrat]

G'day GB.
The correct tension is to be able to turn the belt 90 degrees easily. The problem is if it looses tension for any reason it can rub on the screw boss. With grease in the compartment it won't hurt much but with a boss that has chain damage (most I've seen) it will eat a belt in no time. DAMHIK
Cheers

[Greybeard]

G'day GB.
The correct tension is to be able to turn the belt 90 degrees easily. The problem is if it looses tension for any reason it can rub on the screw boss. With grease in the compartment it won't hurt much but with a boss that has chain damage (most I've seen) it will eat a belt in no time. DAMHIK
Cheers

I checked the instructions. It says to tension the belt to get approx 45° twist each way. Is that what you mean Musky?

I'd like to emphasise that I am not complaining about this failure. The belt has been on for 10 years. I'm happy to be told that my action or lack of attention has caused this to happen.

[muskrat]

G'day GB.
The SRM instructions say 90 degrees. I take it as in one direction.
Cheers

[Dynamo Regulators Mike]

But note that the Dynamo Regulators drive kit differs in this respect from SRM's. Its wider 15 mm belt should twist 45 degrees each way easily from its free position. 90 degrees each way would make it way too loose. The adjustment may seem a little slack with engine cold but the centres move apart with heat so running slack is reduced.

An interesting suggestion regarding a benefit of adding grease to the chamber Musky. Agreed that screw boss is more often than not scored by the chain and contact would readily damage the belt teeth. Certainly running too loose will make the belt jump the pulley teeth, and cause wear at the belt tooth tips. As wear progresses the steel cords between the belt teeth contact the pulley teeth wearing the alloy. Greybeard's photo shows advanced wear from the steel cords. I had never had such wear reported before in 10 years plus of selling the kits.