Wednesday, September 2, 2015

Clutch refurbishment.

Alright, it really was high time I got around to doing this, if nothing else because Witold has been bugging me about this for ssssoooooo long! (but you were absolutely right, and thank you for your usual assistance; thanks bro J)

On my Commando, the diaphragm spring, clutch centre and the metal plates are about the only original parts that remain from the standard clutch: a complete belt drive kit from RGM was fitted and I must say I've had absolutely no issues with it whatsoever, and would strongly recommend it to anyone looking for a belt drive conversion. This means the clutch basket is also a non-standard item.

When it came to putting the actual clutch back together, we went for 4 Surflex fibre friction plates with 3 plain plates and the existing pressure plate, which measures 6.something millimeters, and so should be the thicker type (part n.060745):

Unbeknownst to me at the time, this gave a stack height of 26.something mm, which is simply wrong for my set-up: the diaphragm spring is far too inward, making operation unnecessarily heavy.

Add to that about 20.000kms of use without the slightest bit of maintenance... it's clear that it needed a bit of work.

The new clutch plates, with the existing pressure plate, measure 29.5mm. This appears to be just right.

A note about clutch pressure plates: there are two available, 060745 (5.77mm) is the thick one that goes with 4-friction/3-plain plates, and  063768 (2.72mm) is the thin one that goes with 5-friction/4-plain plates. There are endless tech digest articles on the topic, but if in doubt just contact Andover and they'll help you select the right components.

You guys can do your own conversions to miles, yards, furlongs, rods and ells, millionths-of-an-inch and all that, I'll stick to metric this time.

Now, if I were running a standard clutch basket for the triplex chain, all standard parts in general, then there'd be no excuse for not following what the parts list and workshop manual say: adding extra plates, or tweaking parts in any other way is simply not correct.

But, once you start messing around with non-standard parts, then anything goes. You can take all the measurements you want, in the end what works is mix-matching until you can get the diaphragm spring to be as flat as possible so it can disengage with the least amount of effort. The spring "wants to" push against the plates, so maintaining enough pressure on the plates stack shouldn't be a problem, and the clutch shouldn't slip.

Having considered various options, I decided to follow Mario's advice based on his current experience on his lovely Roadster, and go for a Barnett clutch set, with the addition of a "Dyno Dave" clutch rod seal, a really nifty accessory: 5000+ Commando owners can't be wrong!

Time to get into this thing. The spring compressor is essential if you want to avoid maiming yourself; I've seen it happen and it ain't pretty, believe me.

The back of the clutch adjuster shows a good bit of wear.

The dimpled end of the pushrod is fine.

The other end of the pushrod is just about acceptable, but anyway both the pushrod and the adjuster will be replaced; more on that later.

Once into the clutch stack, the biggest problem is readily apparent: oil contamination, and lots of it.

Especially in the photo above you can see it pool at the lowest point of the clutch basket.
It's obvious that this is 80w90 gear oil, there is no mistaking that rancid smell.
Now, just to be clear, the clutch on the Norton Commando is meant to be a dry clutch, always. Even when running the original triplex primary chain in its oil bath, the clutch is still dry. The little bit of oil that's in the primary chaincase is there to lubricate the chain, not the clutch. And provided you keep the level where it should be (below the basket) there shouldn't be any issues.
Gearbox oil, however, travels the length of the mainshaft, along the pushrod, and eventually spills over inside the clutch. To remedy this, a clever little nut with an O-ring is available to effectively seal the mainshaft. Look for "DynoDave clutch rod seal" and you'll find all the info you need.
I forgot to take a photo of the nut in position, but you can imagine how it screws onto the end of the mainshaft, simple and very clever.
But I'm getting ahead of myself.
Upon inspection, the friction plates show a fair amount of wear, though I've seen much worse. The eccentric grooves were all gunked up with gear oil, while the metal plates were entirely coated. I've cleaned everything and put it aside since, as the mantra goes, "you never know".
The clutch center, or hub, is really not in bad shape, sure the splines show a few marks but there are no notches or anything that the plates can get stuck on:
Next, I gave the clutch basket and hub a proper clean, using a strong degreaser/brake cleaner and a clean cloth to get into all the grooves. This is tedious bloody drudgery but it has to be done, or you'll be back to square one before you even get started. I was careful not to spray any of the degreaser onto the belt just in case the material could be affected by the chemicals.
There, much better. Time to fit the new clutch plates, starting with a friction plate:
Normally, this clutch type with the 5 friction and 4 metal plates, plus thin pressure plate, was fitted to the later 850s, and starting with a friction plate, you also end the stack with a friction plate, followed by the thin pressure plate. However, in this case there is just enough room to fit the thick pressure plate and still be able to properly secure the diaphragm spring with the large snap-ring. This seems to make the diaphragm spring sit almost totally flat, but anyway I'll have to test it and see how it actually works.
Above, you can see the complete stack with the thick pressure plate but no diaphragm spring.
From an angle, to show the minimal room available to fit the diaphragm spring between the pressure plate and that groove in the clutch basket, which is for the large retaining snap-ring. This is an optimal arrangement for a very light clutch action with positive and reliable engagement.
Having removed the pushrod for inspection, a common problem occurred, which could leave you stumped if you don't know what has happened: you put everything back together, try the clutch lever... and nothing happens other than a horrible spongy sensation, but the clutch doesn't work. In all likelihood the clutch actuating arm is the culprit, and if you open the small inspection cover on the gearbox, you'll see that it has fallen down from where it should normally sit. This happens when the pushrod is removed, so frequently in fact that it is even detailed in the workshop manual:

There is no sorcery at play here, and you can fix it yourself without having to sacrifice a goat to whatever "specialist" tells you that only they can get your bike to ever work again. Screw the lot of them, sic semper tyrannis.
You can usually use one finger to push the actuator back in place without having to remove the gearbox cover.
In this case, I actually had to remove the cover to fix yet another problem: the entire clutch operating body was loose in the gearbox, and its lockring was coming undone! Who knows how long it had been like that but this is serious. Thankfully I noticed it and I can fix it.
First of all, with the gearbox cover removed (above), you can see the actuator in the wrong position, it has fallen all the way down.
And above, where it's supposed to be. To keep it there you have to maintain some pressure on the pushrod from the clutch side, or you'll have to start all over again. Getting a buddy to help you makes this a lot easier, but it is not impossible to do it on your own.
As for the clutch operating body, checking to be sure that it is aligned with the passage for the clutch cable, I can now tighten the lockring. I should have done this with a proper pipe tool, but I don't have one so hammer and drift it was.
While I was at it, I also inspected the ratchet mechanism and changed the gearbox oil.
With everything properly and firmly back in place, it's time to test the clutch lever: the result is definitely a lighter feel than before, and it seems to disengage by pulling with just two fingers, something that was impossible previously.

Now it's time for a test ride: I'm weary of hyperbole, but in this case I think it is appropriate to say that this doesn't just feel like a better clutch, it feels like a better motorcycle. Being able to operate the clutch so easily and so quickly means that shifting gears is a lot faster and it becomes something that happens "in the background" so you can focus on actually riding the bike. This was the case during our recent trip to Abruzzo, and it made for a much more enjoyable experience.

There is one more thing I will be fitting to the clutch to complete the upgrade, but first I want to use it like this for a little while, to see how the new clutch plates compare with the old ones in terms of smoothness of operation, engagement, etc. Once I'm satisfied with that I'll get back in there and fit a cool bit of kit...
It's not like me to brag, but I will this time: I've done "un ottimo lavoro" with this, it's much better than it was before.


Buck in Willcox said...

Hi John - The first Commandos had the severest clutch pull I've ever experienced. A lot of people tried a lot of ways of changing the geometry of the ball actuator and it's ramp/cable connect. We all carried spare clutch cables because more than one upper barrel would pull off during any group ride. The pressure plate never got to an over-center condition where the pull would slack off so unless you'd caught neutral before stopping at a light your forearm would be burning before the light turned green. I started experimenting with extra plates to get the pressure plate closer to or at the over-center point where it eased off considerably. That was a dance because too much plate thickness and it'd slip. Lots of time surfacing bronze plates. I did that a lot. Then one day I pulled a clutch to get at something else and the pressure plate was half the thickness of any pressure plate I'd encountered. There were two more plates stacked in standard fashion, not two drive or two driven as we'd had to do for our 'bodge job'. Called my parts supplier and he had a part number for 'em - I ordered 4.

Tales from before the Enlightenment. Buck
Good job you've done there...

Artie said...

Thanks for writing Buck! In the past I have also experienced exactly what you say: a very heavy clutch pull as standard on most Commandos, snapped cables and all the rest of it. The fact that I was able to improve my clutch so easily and so noticeably is down to the fact that so many have gone before me and worked out the kinks, so for example the Barnett clutch kit was a true "ready to fit" item that required no other intervention on my part. I talk about this in this other post ( and, to paraphrase Newton, it's undeniable that if Commando owners today have seen further it is by standing on ye sholders of Giants.
Ride safe and have fun!

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