Notched clutch centre?

Fast Eddie · Sep 24, 2024

SteveA said:
Norman uses a Commando centre as a base for his. That means to me that he gets them from AN. The one I have predates 2016 by a couple of years, my clutch was built in 2014.

The modifications firstly remove the dependence on a standard Commando mainshaft circlip. Essentially a washer is welded to the centre and is clamped by the but onto the mainshaft end.

In my application with a TTi mainshaft I don't think this approach is as necessary, since the mainshaft has a step to it's larger diameter and that step normally retains the clutch centre.

The other part is a little more critical to clutch function. Norman puts a spacer inside, between the clutch centre and the clutch drum bearing. Suitable sized to ensure engagement of the friction plates on to the centre. This is required to ensure the proper engagement of all of the friction pales with the centre and I understood from Norman that the spacer thickness and therefore new circlip groove location may vary between applications. Depending on the application Norman uses 3 or 4 friction plates as required by the specific bike and intended use, basically I guess it depends how much power the clutch is handling.

Mine is a race bike and has 4. This spacer affects the installation of the centre bearing retention circlip, so he machines a new groove based on the required location.

If I use a standard clutch centre I most likely would need to machine a new groove as required.

The harder the centre, the harder this groove will be to cut. I suspect on a CNW item in particular, it would need to be ground.

So, your old one pre-dates the new harder wearing type… and it still lasted 10 racing years !

Your fix seems simple to me Steve… send your old one to Norman and ask him to make a new replacement. Add in new clutch plates for good measure at the clutch will most likely out last your racing career …!

SteveA · Sep 24, 2024

Fast Eddie said:
So, your old one pre-dates the new harder wearing type… and it still lasted 10 racing years !

Your fix seems simple to me Steve… send your old one to Norman and ask him to make a new replacement. Add in new clutch plates for good measure at the clutch will most likely out last your racing career …!

Norman will happily do that. Certainly, he prefers I send it to him so that he can set it up.

10 racing years is a significant exaggeration due to health and stuff like Covid, but it has had plenty of use.

But he says normally they can be quite heavily notched and not pose a problem. At the moment, I think a new set of steels and pressure plate may be all I need, other than a few track sessions to verify.

However, Norman also tells me that come November 2025, when the lease is up on his premises at Thruxton he will shut shop. So if I am going to the UK in the coming months, I think I should take the clutch and get a centre sorted as insurance

As much as anything, I was hoping guys might share their experience and symptoms of a notched clutch centre.

mdt-son · Sep 24, 2024

SteveA said:
Thanks for the input. I guess what seemed obvious to me wasn't.......35/65 is 35 tooth front pulley to 65 tooth clutch drum, it's an 8M belt profile. Maney drum and others are around 68 teeth.

A 65T clutch drum makes it an interesting option for G15 and P11 bikes. Thanks for the clarification. Sorry to hear Norman will close his shop in a year.

- Knut

SteveA · Sep 28, 2024

mdt-son said:
A 65T clutch drum makes it an interesting option for G15 and P11 bikes. Thanks for the clarification. Sorry to hear Norman will close his shop in a year.

- Knut

Custom, built to my primary ratio requirements. Norman is reluctant to take on new customers now due to the impending retirement, from memory he will be 76 or 77 (he is about 5 years older than me I think) when he closes, so retirement well deserved.

Strictly speaking he is already retired, I remember 2015 I think it was when he told me he was just getting his Norton occupational pension!

However, note that the clutch drum is machined from a third party supplied blank, and that comes with the teeth already machined. If I recall, it was about the limit due to plate size. So you can make your own!

I'm noting a couple more subtleties in the design now I have actually pulled it all apart again. The bearing is inserted from inside the drum, and secured by a plate, rather than circlip. Unlike others that are more like the standard Norton drum and have the bearing inserted from the rear (outside) secured by another circlip. I had forgotten that.

I can see that by using the Norton centre and a pre-cut drum blank, Norman minimises the complex machining to mainly milling/drilling/boring.

SteveA · Sep 30, 2024

marinatlas said:
NORMAN WHITE NARROW CLUTCH CENTRE

TOOTH LENGTH: 3/4"BOSS LENGTH: .770"BOSS DIAMETER: 1 1/4"NO. OF TEETH: 25ALL DIMENSIONS ARE NOMINAL

www.rgmnorton.co.uk

Hi Steve , hope all is well at home , I had seen that on RGM , may be it could help ??

I measured my clutch centre thickness at the external splines and of course it is 3/4" and the boss length is 0.77", as the RGM given dimensions for this part. So it is the same. What isn't mentioned is the circlip groove location.

What I don't know however is the thickness of the external spline and boss sections of a standard Commando clutch centre? Anybody know, have one to measure?

SteveA · Oct 1, 2024

acotrel said:
I have never raced very often and my clutch does not receive a beating. With the Commando 850 motor and a 2 into 1 exhaust, there is never a need to slip the clutch to get out of hairpin bends. The slowest corner on Winton Raceway is a tight hairpin. I usually go around it at about 50 MPH in second gear in the close ratio box, losing traction as I accelerate out. Gearing with the Commando engine can be very deceiving. I once had the experience of building expansion chambers for a two stroke which delivered too much torque. You do not usually realise how much torque you have, until you raise the overall gearing. But if you do that with a wide ratio gearbox, the bike becomes impossible to ride well. A Seeley frame is a major advantage - everything can be done faster. If you are in a corner and struggling to get around, slipping the clutch with a peaky motor is not good.
That notching you mention must be on the face which accepts the load. If your gearchanges are not smooth, the problem might be worse. I usually change up at a bit over 7000 RPM, by backing the throttle off and pressing the lever. I only use the clutch on down-changes. So on up-changes, there is not much impact.

I'm sure you are right Al.....I have no idea how to ride a motorcycle!

BTW, is this the 6 speed close ratio box that you have never actually used?

robs ss · Oct 1, 2024

Sorry Steve to hijack your thread (maybe?) but I just cleaned my clutch and noted that notching of both the centre and basket is getting gradually worse. It is a dry (belt) primary. This is counter to @Brooking 850 's experience (post #7). I use it fairly hard but nothing like racing.
It is a cNw with a bit over 13,000 miles on it.
I am considering buying a spare clutch so that I have spares for everything. I am interested in @Madnorton 's comments (post #19) on different centres. I wonder where Matt's fit in that?
Notching in the basket is not as severe but still clearly evident.
Any helpful advice?
Cheers

SteveA · Oct 1, 2024

robs ss said:
Sorry Steve to hijack your thread (maybe?) but I just cleaned my clutch and noted that notching of both the centre and basket is getting gradually worse. It is a dry (belt) primary. This is counter to @Brooking 850 's experience (post #7). I use it fairly hard but nothing like racing.
It is a cNw with a bit over 13,000 miles on it.
I am considering buying a spare clutch so that I have spares for everything. I am interested in @Madnorton 's comments (post #19) on different centres. I wonder where Matt's fit in that?
Notching in the basket is not as severe but still clearly evident.
Any helpful advice?
Cheers

It's OK, you can redeem yourself by measuring that clutch centre, or the standard one you took off!

robs ss · Oct 1, 2024

SteveA said:
It's OK, you can redeem yourself by measuring that clutch centre, or the standard one you took off!

Sure - what measurement(s) would you like?

SteveA · Oct 1, 2024

robs ss said:
Sure - what measurement(s) would you like?

Thickness at the external splines and the boss length

The equivalent to those shown here:

NORMAN WHITE NARROW CLUTCH CENTRE

TOOTH LENGTH: 3/4"BOSS LENGTH: .770"BOSS DIAMETER: 1 1/4"NO. OF TEETH: 25ALL DIMENSIONS ARE NOMINAL

www.rgmnorton.co.uk

robs ss · Oct 1, 2024

SteveA said:
Thickness at the external splines and the boss length

The equivalent to those shown here:

NORMAN WHITE NARROW CLUTCH CENTRE

TOOTH LENGTH: 3/4"BOSS LENGTH: .770"BOSS DIAMETER: 1 1/4"NO. OF TEETH: 25ALL DIMENSIONS ARE NOMINAL

www.rgmnorton.co.uk

The OD (outside of teeth) is 82mm
The length of teeth is 27.5mm
My plate stack height (loose on bench) is 25.3mm - that's 5 friction plates & 6 steel plates.

Helpful?
Cheers

SteveA · Oct 3, 2024

robs ss said:
The OD (outside of teeth) is 82mm
The length of teeth is 27.5mm
My plate stack height (loose on bench) is 25.3mm - that's 5 friction plates & 6 steel plates.

Helpful?
Cheers

Partially, I think the 27.5mm (1.083") compares to the 3/4" (19.05mm) of the Norman White and RGM supplied part. If you look at the linked RGM item it gives two measurements, this and the boss length.

I wanted to know the equivalent numbers of an AN Commando part, taken from the centre only.

I guess what I should take from this is that your original centre is still in the drum. Thanks, it looks like the Norton part is deeper as suggested, consequently my stack height, since the stack also has fewer plates, that is 4 steels and 4 friction plates, will be much less. The inner steel takes the place of the standard clutch backplate.

robs ss · Oct 3, 2024

SteveA said:
Partially, I think the 27.5mm (1.083") compares to the 3/4" (19.05mm) of the Norman White and RGM supplied part. If you look at the linked RGM item it gives two measurements, this and the boss length.

I wanted to know the equivalent numbers of an AN Commando part, taken from the centre only.

I guess what I should take from this is that your original centre is still in the drum. Thanks, it looks like the Norton part is deeper as suggested, consequently my stack height, since the stack also has fewer plates, that is 4 steels and 4 friction plates, will be much less. The inner steel takes the place of the standard clutch backplate.

Yes - Have not pulled the basket & centre off the bike.
Sorry if this does not help you.
Cheers

SteveA · Oct 8, 2024

Madnorton said:
There are 3 types of Commando clutch centre out there, early types were not case hardened, later 850 types were case hardened, but used the early soft core material. The type sold since around 2016 are case hardened with a tougher core material.

I have corrected post #20. The centre I have is not the same design as the AN supplied standard part.

SteveA · Oct 8, 2024

Brooking 850 said:
I use these in both my race bike and road bike, very good quality and no notching !
The manufacturer sent me one before they went to market to test in my race bike running a Maney belt drive with standard Norton bronze clutch plates . No issue to date

cNw Clutch Center

Direct replacement for any stock type clutch baskets, chain or belt 4340 steel Vacuum heat-treated After the heat-treat process, the bearing surface is machined to ensure that this surface is perfect Finish of gear teeth are of highest standard and far beyond any others we have seen available...

coloradonortonworks.net

I have corrected post #20. The centre I have is not the same design as the CNW supplied part.

Notched clutch centre?

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