Toothed belt 750 generator drive

sfcpiet

sfcpiet

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It seems for some, this would be a solution looking for a problem. For me, I have a very real problem with the stock vee-belt drive. The belts don't last long, start to slip and the inside of the drive cover is simply disgusting...

Despite fitting quality Gates belts, I've gone through about 8 belts over the past 30000km, which imho, is a pretty miserable track record. Both pulleys were in generally good condition, the alloy item on the generator showed a little wear, but nothing dramatic. Two generators were fitted during this spell, the first fully overhauled one was swapped out when the housing simply became an eyesore for another completely overhauled item. The first will again be rejuvenated.

The toothed belt conversion is pretty straightforward and I'm expecting it to outlast me... I'll carry a spare on long trips, but that's more for peace of mind. Total outlay was around ā‚¬90, the toothed belt costs about the same as the vee-type, but will probably be easier to source in the future, vee-belts are slowly but surely disappearing.

piet

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It looks like a nice setup. My MG Norge alternator runs a tooth belt and it stays tensioned and no belt dust or cracks after 70k km.
However this belt upgrade could lead to you to sacrilegious activity like replacing the ignition points with an electronic system.šŸ˜
 
You selling kits Piet?
I've had a 750 of some sort for 50 years now, collectively ridden probably well over 300,000 kays and can only remember replacing that V belt a couple of times. Maybe they don't make V belts like they use to. As the crank end is the starter clutch how do you change the V to a tooth?
I like the idea of the upgrade. Maybe someone could be bothered to make replacement kits if there was enough interest.
 
My original SF1 didn't chew up V-belts and I don't think I replaced all that many (usually when I saw splits on the narrow inside V section). When I 'upgraded' to an alternator it was running a 1.75:1 ratio, meaning VERY fast alternator speeds at redline, so i decided to run a Gates toothed belt. The first version was the narrow one you look to have fitted, Piet. It broke after a few months so I simply added a section of toothed pulley to the alternator and ran a wider Gates. This proved very reliable, but for some reason the 880 hotrod chews them out.

My solution was to change to a Gates mini-V. I dropped the ratio down a little to around 1.3:1 and it looks to have been very successful, no sign of wear or slippage, handled the high RPM of Phillip Island no worries. I'm even planning on dropping the ratio down further, as the ND alternator (from a GPX/Z Kawasaki) produces good volts and amps at idle. I chose the ratio based on my C-C spacing crank-alternator.

Pics show the wider toothed belt: the rooted one lasted only about 500km, the new one was looking like going the same way. My thinking is that the mini-V offers greater tolerance to the jerkiness of the crank at idle revs - the 270 crank no doubt exacerbates the jerks.
 

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Your micro-V I'd call a poly-V. Multiple driving surfaces. I've used a 1 in wide one to drive a supercharger - a 750cc Rootes type.
Blowers - like a large alternator - put the highest loads on the drive when backing off. A little slippage can be a good thing.
I've seen a chain driven Shorrocks shear the nose off a crank when backed off at high revs.
 
I've had a look, I have a toothed belt on my SF2 on the V pulleys. It's probably been there 25 years. It was sold to me by Phil Todd at the time.
I have a spare for the next century.
Paul
 
henrywillms said:
It looks like a nice setup. My MG Norge alternator runs a tooth belt and it stays tensioned and no belt dust or cracks after 70k km.
However this belt upgrade could lead to you to sacrilegious activity like replacing the ignition points with an electronic system.
Click to expand...
Err no it doesn't. Big block Guzzi's run a polyvee belt to the alternator not a toothed belt, see below.

I would be very concerned about fitting a timing belt where a polyvee belt would suffice. Toothed belts transmit all the torsional vibrations to the dynamo and with the two differing polar moment of inertias gawd knows what stresses might have been set up. Switch to a polyvee belt, they exhibit micro slippage that smooths out these torsional loads. Just look at the automotive industry and ask, how many cars have toothed belts (not for cam timing) driving alternators etc? None, there's a reason why that is!
 
Sheesh!! I'm positive this conversation was had less than a fortnight ago on here! You DON'T have a toothed belt, Paul. It might have slits in the inner section but that is NOT a toothed belt.
 
3crider said:
Err no it doesn't. Big block Guzzi's run a polyvee belt to the alternator not a toothed belt, see below.

I would be very concerned about fitting a timing belt where a polyvee belt would suffice. Toothed belts transmit all the torsional vibrations to the dynamo and with the two differing polar moment of inertias gawd knows what stresses might have been set up. Switch to a polyvee belt, they exhibit micro slippage that smooths out these torsional loads. Just look at the automotive industry and ask, how many cars have toothed belts (not for cam timing) driving alternators etc? None, there's a reason why that is!
Click to expand...
Yes, automotive use ribbed belts. Hmmm.
 
3crider said:
Ribbed, polyvee...the same thing. i.e. not a timing / toothed belt.
Click to expand...
Automotive ... the very reason I changed from toothed to multi, mini, micro, poly ... V. Seeing the toothed belt stripped of teeth was the decider. It did interest me that the toothed belt survived a lot longer in the old 750 270 crank motor.
 
An interesting topic. We will see if toothed belts with their rigid drive suffer problems. They are far a simpler job than fabricating a tensioner like all the ribbed belts use.
The belt in video felt tight but battery couldn't keep up. New belt fixed it.
 

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3crider said:
Err no it doesn't. Big block Guzzi's run a polyvee belt to the alternator not a toothed belt, see below.

I would be very concerned about fitting a timing belt where a polyvee belt would suffice. Toothed belts transmit all the torsional vibrations to the dynamo and with the two differing polar moment of inertias gawd knows what stresses might have been set up. Switch to a polyvee belt, they exhibit micro slippage that smooths out these torsional loads. Just look at the automotive industry and ask, how many cars have toothed belts (not for cam timing) driving alternators etc? None, there's a reason why that is!
Click to expand...
Well, time will tell. Until then, the toothed belt will remain.

I've run a toothed belt magneto drive on my Matchless single over the past 12 years/22000km without issues. This replaced the rattly chain, which I wasn't willing to tolerate. The magneto platform can be pivoted, providing tension adjustment for the belt, or the previous chain.

Timing belts in both car and bike engines seem to hold up pretty well, cams don't exactly run buttery smooth... they transmit all manner of alternating loads into their drive train.

I did consider a poly-vee belt, but the necessity of a tensioner providing constant tensioner put me off, next to the non-availability of a half-decent fitting belt, either far too long, or too short by a fair bit. I juggled around with pulley ratios and belt lengths, but couldn't find an acceptable solution. If I had wanted to come up with some sort of tensioner, I may as well have stayed with the vee-belt. :rolleyes:

As it is, the toothed belt is adjusted by shims under the generator mounts. Two engines were thus modded and while one engine required no shims, the other required 0.5mm to get the tension right. Seem to be quite high tolerances in the mounting surfaces on the engine cases and/or genny mounts. The armature of the Bosch generator may have a larger mass than the armature of the Lucas magneto, but I'm fairly confident the belt will cope OK, despite being the same width and pitch as the one in the thumper. Like, we're not talking 20000+rpm, a fairly leisurely 5-6000 should be well within the scope of such a drive train.

Toothed belts are used in all sorts of manufacturing machines for bed and tool feeds, also lots of backward/forward movement, day in - day out, year in - year out. These also need to withstand shock loads, seem to cope OK to me.

The main reason imho that toothed belts are only used where absolutely necessary is cost. The belts themselves may not be much more expensive than the poly-vee type, but the pulleys certainly will be! Where production costs are tallied in cents, this would be a very major consideration. If you ever get a chance to have a peek under the bonnet of a '80s DTM car, you will find toothed belts all over the place, driving just about everything that rotates. Oil and water pumps, ignition rotors, FI pumps, alternators.

piet
 
piranha-bro2 said:
Sheesh!! I'm positive this conversation was had less than a fortnight ago on here! You DON'T have a toothed belt, Paul. It might have slits in the inner section but that is NOT a toothed belt.
Click to expand...
So, this is not a toothed belt?
Whatever, it's been on the bike for the last 80 000 km. Works fine.
Paul
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