RGM belt wheel alignment issue.

fiatfan · Mar 24, 2026

850 engine and a "bitsa" gearbox, all restored, all in it´s place. When I use a straight edge on the clutch wheel and measure the distance from that in to the outer edge of the front belt wheel, it turns out that the clutch wheel is 1mm further out (0.04"). I don´t have any schims behind the clutch, just the spacer. There is an 11mm edge on the clutch wheel outside the teeth, but there is 12mm from the straight edge to the outer edge on the front wheel teeth. How can this effect the belt, if it at all will?

concours · Mar 24, 2026

fiatfan said:
850 engine and a "bitsa" gearbox, all restored, all in it´s place. When I use a straight edge on the clutch wheel and measure the distance from that in to the outer edge of the front belt wheel, it turns out that the clutch wheel is 1mm further out (0.04"). I don´t have any schims behind the clutch, just the spacer. There is an 11mm edge on the clutch wheel outside the teeth, but there is 12mm from the straight edge to the outer edge on the front wheel teeth. How can this effect the belt, if it at all will?

Pics please.
Where are the belt guides located on the sprockets?

baz · Mar 24, 2026

fiatfan said:
850 engine and a "bitsa" gearbox, all restored, all in it´s place. When I use a straight edge on the clutch wheel and measure the distance from that in to the outer edge of the front belt wheel, it turns out that the clutch wheel is 1mm further out (0.04"). I don´t have any schims behind the clutch, just the spacer. There is an 11mm edge on the clutch wheel outside the teeth, but there is 12mm from the straight edge to the outer edge on the front wheel teeth. How can this effect the belt, if it at all will?

The front pulley has the belt guides there's none on the clutch
You need to spend some time with the double adjuster on the gear box getting the belt to run true
As long as the full belt is on the clutch and it doesn't wander you are good to go

Metisse11 · Mar 24, 2026

I run a couple of RGM belts on two of my Commando's and always set up the alignment with the inner primary chaincase removed and also us a double sided tensioner.

cliffa · Mar 24, 2026

fiatfan said:
850 engine and a "bitsa" gearbox, all restored, all in it´s place. When I use a straight edge on the clutch wheel and measure the distance from that in to the outer edge of the front belt wheel, it turns out that the clutch wheel is 1mm further out (0.04"). I don´t have any schims behind the clutch, just the spacer. There is an 11mm edge on the clutch wheel outside the teeth, but there is 12mm from the straight edge to the outer edge on the front wheel teeth. How can this effect the belt, if it at all will?

Do you have the spacer behind the clutch in the correct way round? The recessed side should face the sprocket, covering the circlip on the shaft.

fiatfan · Mar 25, 2026

cliffa said:
Do you have the spacer behind the clutch in the correct way round? The recessed side should face the sprocket, covering the circlip on the shaft.

Yes it´s the right way around.

fiatfan · Mar 25, 2026

To everyone; it´s not a question of not having the crank and gearbox shaft aligned, that is sorted. It´s the clutch belt wheel that is slightly too far out compared to the front pulley. It´very little, so I ´m not sure it matters at all. But I can´t move the front pulley outwards, and I can´t get the clutch further inwards, towards the gearbox. Tomorrow I´ll install everything in the primary and turn the engine and see if the belt behaves itself.

concours · Mar 25, 2026

fiatfan said:
To everyone; it´s not a question of not having the crank and gearbox shaft aligned, that is sorted. It´s the clutch belt wheel that is slightly too far out compared to the front pulley. It´very little, so I ´m not sure it matters at all. But I can´t move the front pulley outwards, and I can´t get the clutch further inwards, towards the gearbox. Tomorrow I´ll install everything in the primary and turn the engine and see if the belt behaves itself.

This has already been answered, above, by Baz.

"As long as the full belt is on the clutch and it doesn't wander you are good to go"

His words are accurate. I've got 45 years experience setting up cog belt drives and sprockets. I agree.

Andy Higham · Mar 25, 2026

Does the belt overhang the clutch pulley?

kommando · Mar 25, 2026

The belt has not been fitted, once it has the Baz identified penny will drop.

Schwany · Mar 26, 2026

The clutch basket/pulley should be out further than the crank pulley. Don't worry about it.

Read what Roger's instructions say about tensioning the belt once you get to that point. Kind of important, since the AT10 belt is a little different from other kits with more flexible HTD belts.

RGM belt wheel alignment issue.

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