Alton starter with RGM belt drive

biker_smith · Sep 26, 2020

Hi all - I've just bought an Alton starter kit and running an existing RGM belt drive primary. The instruction with the Alton are not that specific, other than you have to turn up your own spacer for both an RGM or Norvil belt drive. I've measured the gap between the face of the front pulley (when both the sprag spocket and the starter motor sprocket are inline) and the sprag at around 6mm (no room for the front pulley keeper - so removed that). The supplied spacer has a 4.7mm recess which ensures the sprag has a minumum air gap and when tightened grips on the centre diameter. I can envisage a new spacer to work with the RGM belt drive of 6mm thick with the 4.7mm recess (same as that supplied) and with a large outer diameter of 100mm several mm's thick to act as the front keeper for the belt.
So my questions (at last) - has anyone made this before and have all the correct diamentions for me to machine up?
Can it be made of ali, or needs to be mild steel, due to the torque of the crank shaft nut?
Anyone have a simpler solution to the above?
The bike is a '72 Combat 750 Roadster.
Thanks all - Paul.

baz · Sep 26, 2020

biker_smith said:
Hi all - I've just bought an Alton starter kit and running an existing RGM belt drive primary. The instruction with the Alton are not that specific, other than you have to turn up your own spacer for both an RGM or Norvil belt drive. I've measured the gap between the face of the front pulley (when both the sprag spocket and the starter motor sprocket are inline) and the sprag at around 6mm (no room for the front pulley keeper - so removed that). The supplied spacer has a 4.7mm recess which ensures the sprag has a minumum air gap and when tightened grips on the centre diameter. I can envisage a new spacer to work with the RGM belt drive of 6mm thick with the 4.7mm recess (same as that supplied) and with a large outer diameter of 100mm several mm's thick to act as the front keeper for the belt.
So my questions (at last) - has anyone made this before and have all the correct diamentions for me to machine up?
Can it be made of ali, or needs to be mild steel, due to the torque of the crank shaft nut?
Anyone have a simpler solution to the above?
The bike is a '72 Combat 750 Roadster.
Thanks all - Paul.

I have an Alton with a norvil belt drive
I have the 30mm wide belt
I have a slightly different arrangement on mine as the kit I bought from Yves (a member on here) had modified the sprag to drive the engine sprocket, rather than the original alternator keyway
I modified it in the same way to drive the norvil front pulley
So I had to also remake the front pulley keep
So in answer to your question, I made the front pulley keep from mild steel
I put the radius back on that the original aluminium one had
It works fine
I also upgraded the starter chain to an iwis chain, the iwis chain is slightly wider
If you do this with the 30mm belt you will find the chain runs very close to the belt
A 28mm belt would probably be better
Hope this helps

1up3down · Sep 26, 2020

I have an Alton with a Norvil 30mm belt, I did not have to make up any special spacer or parts, very easy installation

Just recently after 8 years of perfect starting I did have to replace the "plugs" as they had finally sheared and the motor would not turn over $25

biker_smith · Sep 26, 2020

Thanks for the info guys. Regards - Paul.

Dukepaul · Jan 22, 2021

Hi biker-smith,
what was your final solution, I am just in the process of fitting an Alton starter and I also have the Norvil 30mm belt frive with the pulley keepers on both sides, however when I offer this up in a dummy set up ut appears the the sprag sprocket isnt aligned with the starter sprocket, it appears the outer pulley keeper will have to be removed, so I would be interested to hear from you or any one else if they have had the same or similar issue and how they overcame this, has anyone ran the alton starter and norvil belet drive without the outer pulley keeper plate?

Cheers
Paul

Nortoniggy · Jan 22, 2021

I fitted the Alton with Norvil belt drive and used the instructions from Alton to machine the pulley and use their supplied spacer. It worked fine.

Dukepaul · Jan 22, 2021

Hi Nortoniggy, thanks for the response, I had seen this on another post and this will probably be my first go at the setting up, but I find the Alton instructions rather confusing and the ones I received with my kit appear to show a different spacer set up to your method, just one futher question, how far does the spacer protrude from the face of the pulley keeper face? looking at the pictures I am guessing it is only about a millimeter?

Nortoniggy · Jan 22, 2021

I think it was around 1mm. It needs enough to have a clearance between sprocket and sprag, and also for starter chain alignment. I'll try to find the instructions tomorrow.

Nortoniggy · Jan 23, 2021

These are the instructions I followed that came with the starter kit. They are pretty good at replying to email questions if you need clarification.

Dukepaul · Jan 23, 2021

Thanks, I am off to my mates in the next day or so to use his lathe, these instructions are different to the ones on the Alton web site, which shows the spacer for the norvil belt drive is totally different to the way you have done yours and as shown in the instructions you sent me, so I will copy the way you and many others have already done with success.

Dukepaul · Jan 29, 2021

Hi Nortoniggy, just a quick note to say hanks for your support, I have now completed the fitting of my Alton starter and had the old gal firing off the button today.

all the best
Paul

Alton starter with RGM belt drive

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