SRM dynamo belt drive

[Slide]

Hi
I very recently fitted a toothed belt kit restoring my first BSA  - an A7SS. I used the kit from DynamoRegulators. I checked it after only 100 miles when fixing an oil leak and noticed a bunch of hairy metal (looked like wire wool) that had collected around the end of the dynamo shaft.  It was held there by magnetism and was steel reinforcing stripped off one side of the belt, presumably due to the edge of the belt rubbing somewhere. From this short experience I'd say it is not only important to make sure the pulleys aer aligned, but also check the sides of the pulleys are good and are not distorted or sharp-edged. I've now done some precautionary smoothing/rounding of the pulley flanges with emery after what happened. It's back together and running, belt itelf looked ok and was re-usable.
I noticed the sides of the small pulley on mine are made of thin alloy which is easily bent out of shape. I found it is important to use a proper screw-in puller when removing the small pulley to avoid damaging it..

Final bit to add: Because the large pulley attached to the idling gear is oversized with these kits, I found there is very little clearance to the casings. I had to do some trimming of the timing cover internal surfaces in places, to get the cover to fit nicely withouit fowling the edge of the large pully - another potential souce of belt damage.

Happy two-wheel motoring

Mark

[RichardL]

Well, this seems like the topic I need to be in. On the possibility that noise would be reduced by installing a dynamo belt drive, I am in the process of installing the SRM version. I think this might have turned into an if-it-ain't-broke-don't-fix-it project.

There is, maybe, an interesting story of trials and tribualtions to come out of this but, right now, I have a question. The nut retaining the dynamo sprocket didn't come off that easy. With the dynamo on the bike, I improvised an impact-wrench approach (whacked a socket speeded with a sledge hammer), which worked due to the strength of the chain tranferring the force to the engine. So, with the belt drive, what happens when you want to remove the SRM nut? Is the belt as strong as the chain when it comes to this kind of abuse?

Richard L.

[bsa-bill]

it's a taper as you know, if you can get an L shaped lever behind the sprocket/pulley and apply some force by levering against the inner case then a light tap with a hammer will spring the taper.
Always worked for me

[RichardL]

Bill and all,

It really surprised me how tight the sprocket was on the dynamo. It took a s***-load of puller tension and a bit of torch heat to get it to let go. I was surprised that the sprocket didn't get bent in the process. BUT, that wasn't the question I was asking. What I was wondering about was how difficult is it going to be to remove the nut that secures the SRM belt sprocket to the dynamo? I am wondering if the belt can provide all the holding force when loosening the belt-drive nut like the chain did for the chain sprocket nut?

Richard L.

[Briz]

The best way is to lock the sprocket with a diagonal bar between the sprockets. Works fine on belt drives too; just be sure not to damage the ally teeth.
When pulling obstinate tapers off, dont just use puller force. Crank some tension into the puller, then hit the centre bolt with a hammer.

[RichardL]

More about this dynamo belt conversion:

• Decided that that the dynamo drive-end bearing felt worn, so decided to replace both.
• Harder than removing the chain sprocket - removing the tiny circlip that retains the small bearing. Found that my hands did not want to cooperate when trying to operate the circlip spreader in such tight quarters on tiny wire ends. Ended-up getting a very pointy awl under one end and slipping it off. This explanation does not do justice to how much sweat was coming off of me while going through all the experiments and struggling to hold still the armature and circlip in a position in which it could be attacked and while wincing from the awl hole in my finger from a failed attempt.
• My puller was almost useless on the small bearing. Ended-up whacking it with a sledge hammer (are you detecting a theme?) to break the outer race and, then, using a Dremel to grind most of the way through the inner race until its grip was weakend.
• Turns out the drive-end bearing was probabaly fine but, hey, what better time to replace it than while the dynamo's all apart and the new bearing is in hand.
  
• Before starting the changeover to the SRM dynamo belt drive I made a fairly technical audio recording  (you know, with viewable wave-forms) of the engine running with the chain-drive dynamo. More on this when I have the recording with the belt drive.

OK. Back to work.

Richard L.

[RichardL]

Good tip. Thanks, Briz.

[trevinoz]

Richard,
                it sounds as though you should be wearing a blue and white striped apron!
When you reassemble, use sealed bearings. The drive end bearing is usually loose in the housing so a little Loctite is advised.
Didn't you hold the armature in a vice to remove the comm end circlip?
Sometimes the comm end bearing can be levered off with two screwdrivers between the bearing and the commutator, after inserting steel packers.
If this doesn't work, a small bearing seperator does the job.

Trev.