Clutch advice....

Bonzo · 2026-05-17T03:51:14-0600

'74 Mk2.

I've just got back from a return visit to the motherland (Wolverhampton).

The bike ran great. Better than it ever has since I've had it. Engine pulled strong with a wonderful, even tick-over at the lights. Handling is sublime, and I know that is down to the CNW head steady that I recently fitted, keeping things taught.

The only issue I had was with the clutch.

When I first got the bike 4 years ago, the original clutch was heavy at the lever. I then substituted one of the plain plates for an RGM 3mm and fitted a Venhill featherlight cable. It was fabulous! As light as a modern hydraulic clutch.

Over the past winter I did a few jobs on the Commando. One of them was to swap the original 20T gearbox sprocket for a 21T. While in there, I noticed that the clutch hub was notched and so bought a new hardened one from CNW. I thought I'd try the Barnett clutch plates as well and this too was a wonderfully light clutch. I use about 150cc of ATF Dexron is the chaincase, and this keeps the chain lubricated. Chain tension is right.

On my trip however, I noticed that, once warm, the plates would 'clonk' right at the bite point. Doesn't happen until the bike has thoroughly warmed up. Best way to describe it is, when approaching a T-junction on an incline, checking it's ok to proceed and then moving off, I'm giving the bike a few more revs than moving away on a flat, and as soon as the clutch disengages it clunks. I'm conscious that now I have a slightly higher gearing (21T) that I'm probably slipping the clutch a little more when moving away.

While in the Midlands, I called up the local dealer to enquire about trying some Surflex plates. He told me that rather than flog me a new set, try putting a plane plate in first and seeing if that makes any difference. I didn't try that as I have 5 x friction & 4 x plane in at the time. I had my phone boroscope with me and couldn't see anything frightening in the primary.

Anyway, I'm back home now and about to 'go in' and have a look inside the primary. I also have the option to put the original plates (with 3mm plain) back in.

Has any one else noticed this with their Barnett plates?

YING · 2026-05-17T04:33:20-0600

Bonzo,
You could try to email Matt at CNW to see if he has any thoughts on your clunk. I have the same setup as you and am trying to imagine the noise you are experiencing. I don’t think it has anything to do with going to a 21T sprocket as long as it was installed correctly.
Just my thoughts.
Mike

concours · 2026-05-17T04:37:23-0600

Bonzo said:
'74 Mk2.

I've just got back from a return visit to the motherland (Wolverhampton).

The bike ran great. Better than it ever has since I've had it. Engine pulled strong with a wonderful, even tick-over at the lights. Handling is sublime, and I know that is down to the CNW head steady that I recently fitted, keeping things taught.

The only issue I had was with the clutch.

When I first got the bike 4 years ago, the original clutch was heavy at the lever. I then substituted one of the plain plates for an RGM 3mm and fitted a Venhill featherlight cable. It was fabulous! As light as a modern hydraulic clutch.

Over the past winter I did a few jobs on the Commando. One of them was to swap the original 20T gearbox sprocket for a 21T. While in there, I noticed that the clutch hub was notched and so bought a new hardened one from CNW. I thought I'd try the Barnett clutch plates as well and this too was a wonderfully light clutch. I use about 150cc of ATF Dexron is the chaincase, and this keeps the chain lubricated. Chain tension is right.

On my trip however, I noticed that, once warm, the plates would 'clonk' right at the bite point. Doesn't happen until the bike has thoroughly warmed up. Best way to describe it is, when approaching a T-junction on an incline, checking it's ok to proceed and then moving off, I'm giving the bike a few more revs than moving away on a flat, and as soon as the clutch disengages it clunks. I'm conscious that now I have a slightly higher gearing (21T) that I'm probably slipping the clutch a little more when moving away.

While in the Midlands, I called up the local dealer to enquire about trying some Surflex plates. He told me that rather than flog me a new set, try putting a plane plate in first and seeing if that makes any difference. I didn't try that as I have 5 x friction & 4 x plane in at the time. I had my phone boroscope with me and couldn't see anything frightening in the primary.

Anyway, I'm back home now and about to 'go in' and have a look inside the primary. I also have the option to put the original plates (with 3mm plain) back in.

Has any one else noticed this with their Barnett plates?

No.

Bonzo · 2026-05-17T04:49:03-0600

Inside of the primary looks fine.

I'll pop the plates out and examine them. Might even try substituting a couple of the Barnett frictions for the original bronze ones. I'll see what the stack height is.

Bonzo · 2026-05-17T05:13:15-0600

These are the plates as they came out - I haven't cleaned them yet.

The friction plates look fine, but the plane looked marked (they're not scored at all)

concours · 2026-05-17T05:32:27-0600

That is material inconsistency from the raw steel coil. Many look the same. That won't cause the symptom you describe.

MikeG · 2026-05-17T05:57:53-0600

I never had a clonk noise but when my were new I would get a chirp like a bird being stepped on at engagement point. Same basic setup as yours but I had to have a 5th plain plate surface ground down to get proper stack height.

Bonzo · 2026-05-17T06:02:32-0600

MikeG said:
I never had a clonk noise but when my were new I would get a chirp like a bird being stepped on at engagement point. Same basic setup as yours but I had to have a 5th plain plate surface ground down to get proper stack height.

Cheers Mike, good feedback.

I'm off to attempt to capture a bird, purely for test purposes

franko · 2026-05-17T06:59:49-0600

I've had to work on my clutch and also the clutch on a retirees bike, that I got running for him again. The plain plates in both bikes needed to be dressed. I used sandpaper on plate glass. Working in a figure 8 pattern. I did it to remove all high spots. It took awhile. I removed some of my fingerprints. Having the plates flat made a big difference. I don't know if it made a difference, but both bikes are running the bronze friction plates.

Carl H · 2026-05-17T07:38:51-0600

I wouldn't think the aluminum Barnett plates could clunk . I would: Check for other issues. You could run the bike with the Primary cover off for a brief test to see if that helps you locate the sound and you could quickly do a few changes to the plate set up to see if that helps and even feel the how the clutch releases and how the clutch feel feels. **BEcareful with an open cover as you don't want to get any parts of your body caught in the chain /sprockets.

When you have all the plates out, turn the mainshaft and clutch center to see if you can make the clunk you hear. Is the alternator rotor clunking? Or an internal trans part? Is something clunking in the clutch release mechanism? Put the bike in different gears and see if that makes it clunk when you do the turning tests.

Also spin the rear tire back and forth to see if you can make it clunk with the bike in and out of gear. You just put a 21 tooth sprocket in the bike, so you need to double check your work.

I'm a firm believer in Transmission inspections , you never know what you will see. Late model 850s Mk2s can have the defective Lay shaft bearing in them. Draining the transmission lube might show metals in the lube.

Hortons Norton · 2026-05-17T08:19:04-0600

Those plates don't look like they have any oil on them? If they are still dry try wiping them down with a oily rag and see if that helps.

concours · 2026-05-17T08:48:53-0600

Hortons Norton said:
Those plates don't look like they have any oil on them? If they are still dry try wiping them down with a oily rag and see if that helps.

O.P.: "I use about 150cc of ATF Dexron is the chaincase"

To the risk of igniting a flame festival here, I use a LOT MORE than the factory specified amount, to the joy of my clutch, stator & chain.

No downside to doing this, filled to just cover the bottom chain run.

Bonzo · 2026-05-17T09:48:35-0600

So, I re-installed the clutch plates, after giving the Barnett friction pads a bit of a soaking in ATF for ten minutes and they drying them off. I replaced two Barnetts with original bronze plates and before I clipped them in, offered up the 3mm RGM plain plate to check the height. It fit in a treat and so I'm just back from a 15 mile demo run where I deliberately tried to get it to make the noise I was experiencing earlier, by pulling over on steep inclines and setting off again, etc. The upshot is that I couldn't get anything other than a perfect take off. Smooth, quiet and really light

I can only put it down to having an incorrectly adjusted clutch earlier

I don't know what the depth of the Barnett friction plates are vs the original bronze ones, but I'll check later, and maybe change back to the 5 Barnetts. It could be that all it needed was the 3mm plain in place of the standard.

I've also been thinking about my description as a 'clunk'. I don't know if that was what it really was. All I can say is that at the bite point, it was fierce for a split second.

Anyway, for now - all good

Thanks for your comments folks

Clutch advice....

Bonzo

YING

Pittsboro,NC

concours

Bonzo

Bonzo

concours

MikeG

Mikeg

Bonzo

franko

Carl H

Hortons Norton

concours

Bonzo

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