Notched clutch centre?

I have a TTi box and a Norman White belt drive and clutch. The clutch centre is a modified Commando item that Norman uses, the mods relate purely to the location on the gearbox shaft. Everything else is different to Commando, but enough is similar that similar issues are possible.

As it gets hotter, read after maybe 4 laps of Carole which short but has 2 hairpins.....so the clutch gets some abuse.....and even hotter if you have to slip it in second out of the hairpins.

It gets progressively more difficult to select first gear, which is a bugger because you need it twice. Though it's possible the issue is affecting all down gear changes, it doesn't become an unmanageable problem until it can drop in to neutral instead of first, where it stays.

The last time I stripped it, I did note some notching on the clutch centre. Lots of other things in life got in the way, like health, so here we are at least a couple of years later, possibly 'rediscovering' the issue.

Has anyone had similar symptoms?

What did you trace them to?

What plates are in the clutch? (Type/brand)
Any discoloration on the steels?

concours said:

What plates are in the clutch? (Type/brand)
Any discoloration on the steels?

Click to expand...

Norman uses the AJS Stormer plates, they are sintered bronze coated steel. These are pretty much what he used on the JPS bikes in the '70s!

They are smaller than Commando items, the ratio is 35/65. The main benefit of his clutch is it's smaller and lighter, less rotating mass.

Steels seem OK, though possibly a little new discolouration over last time (I've just pulled them out, I need to do a more thorough examination).

Friction plates are recent in as much as they were replaced when the bike was last used in 2022, it had been slipping under load due to wear beyond minimum thickness.

There does seem to be a build up of friction material where the steels meet the drum. Needs a good clean. Replacing the steels is certainly a consideration anyway.

There is notch marking on the centre, but it's not 'severe'.

SteveA said:

Norman uses the AJS Stormer plates, as he did on the JPS bikes in the '70s! They are smaller than Commando items. The main benefit of his clutch is it's smaller and lighter, less rotating mass.

Steels seem OK, though possibly a little new discolouration over last time (I've just pulled them out, I need to do a more thorough examination).

Friction plates are recent in as much as they were replaced when the bike was last used in 2022, it had been slipping under load due to wear beyond minimum thickness.

There does seem to be a build up of friction material where the steels meet the drum. Needs a good clean. Replacing the steels is certainly a consideration anyway.

There is notch marking on the centre, but it's not 'severe'.

Click to expand...

As a test, Try NOT abusing the clutch and see if the (clutch) performance degrades, or stays consistent.

I've seen some friction material swell when heated.

Buy some new parts, racing gobbles up parts.

Difficulty in finding first can be caused by a tight primary chain, so worth checking that and if a belt then the heat build up may be getting that too tight too.

SteveA said:

Norman uses the AJS Stormer plates, they are sintered bronze coated steel. These are pretty much what he used on the JPS bikes in the '70s!

They are smaller than Commando items, the ratio is 35/65. The main benefit of his clutch is it's smaller and lighter, less rotating mass.

Click to expand...

The quoted ratio is the ratio of areas, I guess?

The NW clutch appears to be unsuitable for the circuit you are racing on! Why not replace the NW clutch by another full-size clutch, e.g., the Steve Maney clutch?
Is the reduced mass moment of inertia worth the trouble you are experiencing? For a clutch basket made of aluminum or even titanium, the drive torque (= change in angular momentum) required to accelerate each of them will likely be subordinate to the momentum required to accelerate the crankshaft.

Change of angular momentum is: delta_D = M*t = J * delta_Omega

D angular momentum (Nm*sec)
M*t drive torque (Nm*sec)
j moment of inertia (kg*m^2)
Omega angular speed (1/sec)

The flywheen of a Norton (approximated by 2 discs ø10in and 0.5in thickness each) has a moment of inertia of J = 0.25*m*D^2 = 0.163 kg*m^2
(the rotating mass is 22.3 lb in this example).

Now, what's the moment of inertia of your clutch? And J of a standard Norton clutch?

- Knut

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

mdt-son said:

The quoted ratio is the ratio of areas, I guess?

The NW clutch appears to be unsuitable for the circuit you are racing on! Why not replace the NW clutch by another full-size clutch, e.g., the Steve Maney clutch?
Is the reduced mass moment of inertia worth the trouble you are experiencing? For a clutch basket made of aluminum or even titanium, the drive torque (= change in angular momentum) required to accelerate each of them will likely be subordinate to the momentum required to accelerate the crankshaft.

Change of angular momentum is: delta_D = M*t = J * delta_Omega

D angular momentum (Nm*sec)
M*t drive torque (Nm*sec)
j moment of inertia (kg*m^2)
Omega angular speed (1/sec)

The flywheen of a Norton (approximated by 2 discs ø10in and 0.5in thickness each) has a moment of inertia of J = 0.25*m*D^2 = 0.163 kg*m^2
(the rotating mass is 22.3 lb in this example).

Now, what's the moment of inertia of your clutch? And J of a standard Norton clutch?

- Knut

Click to expand...

Love it when we resort to physics equations to explain things!

ilikevelos said:

Love it when we resort to physics equations to explain things!

Click to expand...

I'm a Duh , but amusing .

ilikevelos said:

Love it when we resort to physics equations to explain things!

Click to expand...

Yeah, what wrenches work best on an equation.