Commando 750 clutch set up on a N15CS - bad clutch slip

I’m just finishing the restoration of a Norton N15CS, the motor and gearbox have been rebuilt and it has a Commando clutch assembly fitted.

It’s easy to start, runs well and has plenty of power. But there's one thing that has me completely bamboozled and frustrated. The clutch slips like crazy as soon as warms up a little.
All the clutch parts are new - mainly from Andover Norton.
The clutch worked fine for about 30 miles - then started slipping.
There is no oil on any of the fibre or steel plates, I put in 200ml of 20/50 oil.
I’ve had the clutch out and back about 10 times, with different configurations, but the same result - lots of clutch slip. Here’s what I’ve tried so far:

Setup 1: 7.05mm pressure plate; 4 3.60 mm barnett fibre plates ; 3 2.00mm steel plates; 1 1.80 mm steel plate - total 26.92m
Setup 2: 7.05mm pressure plate; 4 3.60 mm barnett fibre plates ; 3 2.00mm steel plates; 1 1.80 mm steel plate - total 29.23mm
Setup 3: 2.71mm pressure plate; 5 3.60 mm fibre plates ; 2 2.00mm steel plates; 2 1.80 mm steel plates - total 28.34mm

For the life of me, I can’t work out what I’m doing wrong. I have an 850 Commando with the same clutch and have never had any problems at all.

Can anyone shed some light on how I might be able to resolve this? Its driving me nuts!

Are you certain there's no oil on the plates?
As you no doubt know 20/50 motor oil can make the clutch slip
ATF is recognised as being best in a chaincase

I'm assuming you have a commando main shaft in your gearbox?

markaust18 said:

Setup 1: 7.05mm pressure plate; 4 3.60 mm barnett fibre plates ; 3 2.00mm steel plates; 1 1.80 mm steel plate - total 26.92m
Setup 2: 7.05mm pressure plate; 4 3.60 mm barnett fibre plates ; 3 2.00mm steel plates; 1 1.80 mm steel plate - total 29.23mm

Click to expand...

Same plates but different totals?

Sorry you're right - the 1st one only had 3 2.00 mm plates

Taking that N15CS outer primary cover off 10 times would drive anybody nuts. I often do the same thing over and over again inside the P11 primary expecting different results. Basically, I spend a lot of time verifying the definition of insanity. Just one of the many super powers I have.

If the 20/50 oil is synthetic, you are going to have to degrease the plates. Synthetic was too slippery with my clutch. I used a nasty water based degreaser, but I would listen to someone that actually has a Commando for cleaning off the plates, and not me so much, since I still have a 6-spring NEB clutch in it, not a Commando clutch.

This next bit is a little off topic. How did you fit a Commando clutch in the N15CS primary? Did you swap out the stock N15 primary covers for early Commando primary covers? Or, was there enough width inside the stock primary to fit the clutch and 3 row chain? Also as baz mentioned did you install a Commando mainshaft in the gearbox? I don't know if a Commando clutch can be installed without the circlip on the mainshaft, so am curious.

Personally, I'm real tired of wet clutches on my Norton, so am looking at Matt's Commando clutch for my P11. He uses the narrowest belt out there in a kit clutch. Expensive, but may let me use my stock P11 primary covers without a lot of creative effort. My gearbox will have to be moved as far back as it will go, but I think there is enough room to get away with a Commando length belt. Other options exist (RGM for example) for a heck of a lot less money, but the belts would require a different set of primary covers.

Anything I say in this forum may or may not be irrelevant to some members here. I'm working on caring, but it is a hard row to hoe.

My experience with a Commando clutch in an Atlas was..... it was a three way battle to get easy clutch pull, no clutch drag, and no slippage.

Do you have a clutch push rod seal? I know you said no oil on the plates, but just a little oil from the gearbox may slip your notice, and may cause slip.

Do you have sufficient play in the lever? With insufficient play, your clutch push rod may expand when hot and push on the pressure plate.

Slick

Its not just synthetic oil that plays up on clutches but any of the modern car oil with friction modifiers. Use ATF which is designed for auto boxes which contain lots of clutches. You will need to clean the contaminated plates.