Primary belt phenomenon

robs ss

robs ss

VIP MEMBER
Joined
Aug 16, 2016
Messages
3,244
Country flag
Not sure if any of you have seen this before...
It happened just now (9600 miles) and about a thousand miles ago.
When I check the final drive tension, and it is on the loose side, I immediately suspect the primary (belt) has gone a bit tight.
Almost always right.
In earlier miles I would have to play with the (RH) adjuster - no room for LH adjuster with the cNw E-start.
The last couple of times I have not had to touch the adjuster - loosening the lower pivot bolt and the upper bolt immediately gives the desired "play" in the belt (I use the 90 degree twist method - but let's not go there). So, I retension the lower and upper bolts (in that order - does it matter??) and all is great.
I suspect what is happening is the gearbox mounts are able to move slightly, like a spring, on the powder coated cradle, to an extent it slightly loosens the rear chain. Loosening the bolts allows it to spring back to where it should be.
If I'm right, it's an argument against shiny/hard surfaces on the cradle.

Anyone else seen this on their bikes.
It would almost certainly happen in primary chains too (if I'm right :rolleyes: )
Cheers
 
Edit: It's the only bad point (that I know of) about the cNw E-start.
The internal alloy bracket completely obscures any view of the belt through the (middle) chain tension checking port.
Just means the primary cover has to come off.
No biggie, no oil!
Cheers
 
robs ss said:
Edit: It's the only bad point (that I know of) about the cNw E-start.
The internal alloy bracket completely obscures any view of the belt through the (middle) chain tension checking port.
Just means the primary cover has to come off.
No biggie, no oil!
Cheers
Click to expand...
Is there no room at all for a twin adjuster?
I have a belt drive with my Alton
I fitted the left hand adjuster facing backwards for access
 
baz said:
Is there no room at all for a twin adjuster?
I have a belt drive with my Alton
I fitted the left hand adjuster facing backwards for access
Click to expand...
No.... unfortunately there is no room - that I can see anyway.
Maybe someone cleverer?
 
baz said:
No I have an Alton
I had to re drill a new hole and run the adjuster backwards
Click to expand...
Maybe there is someone clever out there but, even reversed, I can't see a LH adjuster working with the cNw.
I know Nigel (@Fast Eddie ) now has one (after that video) maybe he has a perspective?
Cheers

...but my point was more about the gearbox apparently "springing" back into the correct position without playing with RH adjuster.
 
Last edited:
robs ss said:
Maybe there is someone clever out there but, even reversed, I can't see a LH adjuster working with the cNw.
I now Nigel (@Fast Eddie ) now has one (after that video) maybe he has a perspective?
Cheers

...but my point was more about the gearbox apparently "springing" back into the correct position without playing with RH adjuster.
Click to expand...
Yeah I fitted two adjusters, not sure it’s necessary tho?

I cut some of the cast in chain-guard away in the rear of the inner primary case. It’s tight, but just about accessible.
 
Fast Eddie said:
Yeah I fitted two adjusters, not sure it’s necessary tho?

I cut some of the cast in chain-guard away in the rear of the inner primary case. It’s tight, but just about accessible.
Click to expand...
Two adjuster's has been necessary on my commando
Because twice the top gearbox bolt has come loose
I'm pretty sure the twin adjusters saved the belt
 
Belts do not stretch and they are 'repeatable', i.e. a new one of the same spec is the same length. You can change the belt and use the same tension location.

So, once you have the correct shaft distances set, you don't need an adjuster!

So what you can do is remove the threaded adjuster and fit fixed plates. For a Commando I would suggest one each side. The plates can be made from 1/8" mild steel, with a hole for the Gearbox mount and a second hole for a 5/16" or 8mm bolt.

Manufacture and fit the plates. Set the shaft centres. Mark for boltholes in the gearbox plates. Drill holes! (Probably needs a fair amount of disassembly to do this).

Insert bolts. Bolt tight. Gearbox will never move again!

This is a Rickman, it was their method and only used one plate. But you get the idea.
 

Attachments

  • Primary belt phenomenon
    2014-03-29 13.13.45.1.jpg
    274.8 KB · Views: 103
Last edited:
SteveA said:
Belts do not stretch and they are 'repeatable', i.e. a new one of the same spec is the same length. You can change the belt and use the same tension location.

So, once you have the correct shaft distances set, you don't need an adjuster!

So what you can do is remove the threaded adjuster and fit fixed plates. For a Commando I would suggest one each side. The plates can be made from 1/8" mild steel, with a hole for the Gearbox mount and a second hole for a 5/16" or 8mm bolt.

Manufacture and fit the plates. Set the shaft centres. And mark for boltholes in the gearbox plates. Bolt tight, gearbox will never move again!

This is a Rickman, it was their method and only used one plate. But you get the idea.
Click to expand...
Yep when I changed my belt I never adjusted anything
But the top gearbox mounting stud has come loose twice
Having said that it actually hasn't come loose since I removed the maney outrigger
 
SteveA said:
So what you can do is remove the threaded adjuster and fit fixed plates. For a Commando I would suggest one each side. The plates can be made from 1/8" mild steel, with a hole for the Gearbox mount and a second hole for a 5/16" or 8mm bolt.

Manufacture and fit the plates. Set the shaft centres. Mark for boltholes in the gearbox plates. Drill holes! (Probably needs a fair amount of disassembly to do this).
Click to expand...
That is what I did for my N15.
My Commando has a custom-made engine cradle with a fixed position for the gearbox, so doesn't need it.
One on each side:

Primary belt phenomenon


Primary belt phenomenon

The elongated hole for the small bolt allows for a final adjustment of 0.5 mm.
 
ludwig said:
That is what I did for my N15.
My Commando has a custom-made engine cradle with a fixed position for the gearbox, so doesn't need it.
One on each side:

Primary belt phenomenon


Primary belt phenomenon

The elongated hole for the small bolt allows for a final adjustment of 0.5 mm.
Click to expand...

Did you threads cut into the engine cradle hole or...run the bolt through a smooth hole with a nut on the other side?
 
Last edited:
going back to original symptoms: have you tried tensioning the rear chain strongly while doing up lower gearbox bolt:
to make sure box will not go further back when in use, and THEN see if primary goes tight straight away?
 
jan nelder said:
going back to original symptoms: have you tried tensioning the rear chain strongly while doing up lower gearbox bolt:
to make sure box will not go further back when in use, and THEN see if primary goes tight straight away?
Click to expand...
No, I have not, but loossness comes back into the belt when I slacken to top bolt. The bottom had already been loosened.
I like your thinking though - a bit like activating a drum hard whilst tightening an axle. đź‘Ť
I think I'll have a go at the solution offered by @SteveA and @ludwig .
I think the LH side is the problem - but it can wait till I'm in the mood to pull the inner primary off!
Cheers
 
ludwig said:
Threaded hole, no nut.
Click to expand...
I would say the threaded hole is definitely the right choice in steel plates.

Rickman of course has alloy plates. I think I feel happier with the nut, but I doubt threading the high quality aircraft spec material of my plates would be a problem.

The exhaust mounting behind it is 8mm threaded hole, but of course less force is anticipated.

Plate material generously supplied and laser cut to CAD design by an aircraft company in Northern Italy....whilst no one was watching!
 
The rear chain always torques the gearbox backwards and that tightens the primary chain, It's best to start with the primary drive tight then adjust it forwards to get the required tension. This takes all the slack out of the adjusters and prevents it tightening up.
 
robs ss said:
No, I have not, but loossness comes back into the belt when I slacken to top bolt. The bottom had already been loosened.
I like your thinking though - a bit like activating a drum hard whilst tightening an axle. đź‘Ť
I think I'll have a go at the solution offered by @SteveA and @ludwig .
I think the LH side is the problem - but it can wait till I'm in the mood to pull the inner primary off!
Cheers
Click to expand...
Just had an epiphany (I think??) on the "lock plates" used by @SteveA and @ludwig .
In order to give a bit of adjustability to those nice plates - maybe inclusion of a snail-cam in the design.
See pic below where Y would be a "bit" less than X.
Cheers
Primary belt phenomenon
 
You must log in or register to reply here.
Back
Top