Heavy duty Norton Commando Diaphragm Clutch Spring - is there such a thing?

On a lighter note:

Who only uses 2 fingers to pull on the clutch lever? And which 2 are you using? I know it's an irrelevant question. I just want to know what the cool kids are doing.

My diaphragm spring is slightly convex when installed, so purposely a high stack for a light pull at the lever. The clutch probably only works well currently because the frictions and steels are new. I can see myself getting the fat steel plate at the back of the drum surfaced a little in the future, or buying a thinner plate. For now I am enjoying the light pull. I end up using all my fingers on the clutch lever. Hence, I am not cool at all, and could never hang out with the cool kids.

My clutch hub is designed for use on a pre-Commando mainshaft. I think that is the primary difference between it at the diaphragm spring belt clutches used in Commandos. Still it could very well mean all my commentary is irrelevant, since it usually is. lol

Schwany said:

My diaphragm spring is slightly convex when installed, so purposely a high stack for a light pull at the lever. The clutch probably only works well currently because the frictions and steels are new. I can see myself getting the fat steel plate at the back of the drum surfaced a little in the future, or buying a thinner plate.

Click to expand...

As the clutch plates wear, the stack height will reduce. The spring clamping force, therefore, should increase although the clutch pull will also begin to increase once the assembly wears beyond flat and into 'concave'.

L.A.B. said:

As the clutch plates wear, the stack height will reduce. The spring clamping force, therefore, should increase although the clutch pull will also begin to increase once the assembly wears beyond flat and into 'concave'.

Click to expand...

That makes sense. I dropped the logic ball.

L.A.B. said:

Then please explain why not.

Click to expand...

The staggered fingers would be a design attempt to change the over-center point to a "wider" area of engagement (modern pundits refer to it as the "friction zone") for a more linear progressive clutch.

The forming dies are more complex (read that: expensive) to achieve the stagger.


Wether the cost/benefit ratio was justified, was a management choice.

concours said:

The staggered fngers would a design attempt to change the over-center point to a "wider" area of engagement (modern pundits refer to it as the "friction zone") for a more linear progressive clutch.

Click to expand...

Yes, as dynodave had mentioned some time ago...
"3. Flat Zone .45” to .55” of Deflection—The Flat Zone is whenthe diaphragm is approaching flat. This occurs when the two tiers of theclutch fingers are half (9 fingers) inverted and half (9 fingers) extended.This staggered arrangement helps broaden the Flat Zone."

...although I see no actual advantage in a broader flat zone of over-centre engagement if applied to the Commando clutch and I've not heard any reports of the new spring design having different engagement/disengagement characteristics to the original spring.

L.A.B. said:

Yes, as dynodave had mentioned some time ago...

Wayback Machine

"3. Flat Zone .45” to .55” of Deflection—The Flat Zone is whenthe diaphragm is approaching flat. This occurs when the two tiers of theclutch fingers are half (9 fingers) inverted and half (9 fingers) extended.This staggered arrangement helps broaden the Flat Zone."

...although I see no actual advantage in a broader flat zone of over-centre engagement if applied to the Commando clutch and I've not heard any reports of the new spring design having different engagement/disengagement characteristics to the original spring.

Click to expand...

You're right.
I haven't heard either. (If a tree falls in the woods.....)
A narrow engagement point clutch is good for drag racing.
My post was JMWO.

Thank you everyone for the great wealth of information provided. Very helpful indeed! I think I might have found at least part of my problem.....

So, I think some facts are finally starting to sink into my lead lined cranium! My apologies for being a slow learner: It would seem, that as a general rule, the lower the stack height, the greater the pressure applied by the diaphragm spring, the less risk of clutch slip, but consequently a heavier clutch action.

In my experiments I have pushed the limit of "convex", (diaphragm spring central boss pushing outwards) / highest possible stack height. Now I understand that it is actually the other end of the spectrum, "concave" that I need to investigate. The idea being that once I get a clutch that does not slip, maybe I can experiment with a higher clutch stack. However, I have been unable to implement a stack height lower than "flat".

Side note:- When "flat", I noted that the clutch diaphragm did not open correctly when the clutch lever was applied. The clutch diaphragm made a loud clicking noise and the diaphragm spring central boss skewed to one side, such that the pressure on the pressure plate was only partially relieved. I thought this meant that the stack height was too low. Apparently what it actually means is that the diaphragm spring central boss is defective or not centralized for some reason. Or perhaps there is an issue with the clutch actuating rod?

The reason I could not achieve "concave" (diaphragm boss pushing inwards) / lowest possible stack height - and this is the interesting bit - is that the nut on the end of the gearbox main shaft, with integral clutch rod oil seal, may be too tall? It would appear that I may be using the wrong nut! The one I am using is apparently for a Dominator. I think I need a standard nut and a slim type nut with clutch rod seal on top, please see photos attached.

Also, now that I am running a belt drive and consequently my primary case is dry, I see that the clutch rod seal I had installed was not working, as gear oil was clearly seeping from the gearbox into the primary, which is of course likely also part of my problem!

I am going to obtain a slim type clutch rod seal, standard nut, a new diaphragm spring and a few other bits and pieces and then play some more.

I will update this forum if I discover any additional pertinent information.

Kind regards,

James

Britstuff said:

Thank you everyone for the great wealth of information provided. Very helpful indeed! I think I might have found at least part of my problem.....

So, I think some facts are finally starting to sink into my lead lined cranium! My apologies for being a slow learner: It would seem, that as a general rule, the lower the stack height, the greater the pressure applied by the diaphragm spring, the less risk of clutch slip but consequently a heavier clutch action.

In my experiments I have pushed the limit of "convex", (diaphragm boss pushing outwards) / highest possible stack height. Now I understand that it is the other end of the spectrum, "concave" that I need to investigate. The idea being once I get a clutch that does not slip, maybe I can experiment with a higher clutch stack. However, I have been unable to implement a lower stack height beyond "flat".

Side note:- When "flat", I noted that the clutch diaphragm did not open correctly when the clutch lever was applied. The clutch diaphragm made a loud clicking noise and the central boss skewed to one side, such that the pressure on the pressure plate was only partially relieved. I thought this meant that the stack height was too low. Apparently what is actually means is that the diaphragm spring boss is defective or not centralized for some reason.

The reason I could not achieve "concave" (diaphragm boss pushing inwards) / lowest possible stack height - and this is the interesting bit - is that the nut on the end of the gearbox main shaft, with integral clutch rod oil seal, may be too tall? It would appear that I may be using the wrong nut! The one I am using is apparently for a Dominator. I think I need a standard nut and a slim type nut with clutch rod seal on top, please see photos attached.

Now that I am running a belt drive and my primary case is dry, I also note the clutch rod seal I had installed was not working and gear oil was clearly seeping from the gearbox into the primary, which is of course likely also part of my problem!

I am going to obtain a slim type clutch rod seal, standard nut, a new diaphragm spring and a few other bits and pieces and then play some more.

I will update this forum if I discover any additional pertinent information.

Kind regards,

James

Click to expand...

Also throw that soft mild steel tab washer away and use locktite instead

Britstuff said:

The reason I could not achieve "concave" (diaphragm boss pushing inwards) / lowest possible stack height - and this is the interesting bit - is that the nut on the end of the gearbox main shaft, with integral clutch rod oil seal, may be too tall? It would appear that I may be using the wrong nut! The one I am using is apparently for a Dominator. I think I need a standard nut and a slim type nut with clutch rod seal on top, please see photos attached.

Click to expand...

Yes, the tall pushrod seal nut could very well be the problem. RGM Motors used to sell a tall pushrod seal nut like the one you have for the Commando which was often found to be too tall and could clash with the spring boss.

It's possible you have one too many steel washers behind the nut. The early assembly had the nut and a spring washer. Your 850 would have had the tab washer (the one baz said to remove, up to you if you do?) and a hardened steel washer.

The stack height in your picture doesn't look too high so the tall seal nut could've prevented the spring from pressing fully on the pressure plate.

If you replace the seal nut you will also need the standard clutch centre nut (if you don't have one) when you fit the dynodave seal nut...
Edit: Deleted as you'd mentioned buying the nut.
...you might already have the hardened steel washer.

Britstuff said:

Also, now that I am running a belt drive and consequently my primary case is dry, I see that the clutch rod seal I had installed was not working, as gear oil was clearly seeping from the gearbox into the primary, which is of course likely also part of my problem!

I am going to obtain a slim type clutch rod seal, standard nut, a new diaphragm spring and a few other bits and pieces and then play some more.

I will update this forum if I discover any additional pertinent information.

Kind regards,

James

Click to expand...

More possibly useless clutch related information:

Below are images of the latest RGM Commando mainshaft clutch rod seal with nut. It measures .748" in height and the seal can be adjusted in or out inside the nut center. The pre-Commando rod seal nut is taller and what I am using with just the hardened steel washer and the tab washer on a pre-Commando mainshaft. No interference with the RGM diaphragm spring/adjuster cup combo. I used a high temperature silicon sealer on the brass rod seal threads. Probably wouldn't hurt to do the same or use blue loctite on the nut threads if one was to use this clutch rod seal.

Good to hear you're getting to the bottom of the problem.
I've never found the stack height to be that critical, provided the correct pressure plate is used for the type of plate set up, i.e. thick (and heavy!) 750 vs. thin 850.

I've found the old style RGM nut with oil seal needed around 1/8" machined off before it would allow the clutch to function correctly. I still use them, but I'm glad I have a lathe
The one in Schwany's post is definitely going to need machining down for Commando use. Beats me why they supply them like this?

Gear oil could be seeping in past the mainshaft high gear bushes, which could indicate some future gearbox refresh work.

Thank you L.A.B. and Schwany!

B+Bogus got me thinking.....

To date I have given some thought to stack height, but I have not really considered the constituent parts of the stack itself. I want, (at least for now) to try to lower my stack height to increase pressure on the pressure plate. I know I am going to use a thin pressure plate. However, how many fiber plates? Right now I have a couple of sets, one surflex and one Barnett, (both sold as compatible with 850), In both cases 4 plates only. Some out there in the big wide world would perhaps suggest 5 fiber plates for the 850? O.K. if that is so, the stack height is therefore going to be higher. So does using a 5th fiber plate, with presumed lower pressure on the surface of the pressure plate because of increased stack height, compensate for such because of the increased friction potential of a 5th fiber plate?

Anyway, the question is: on an 850 which is better, 4 fiber plates or 5? Or does this question only really apply to bronze type friction plates, (which I think have always been 4 for 750 and 5 for 850)?

Britstuff said:

I know I am going to use a thin pressure plate.

Right now I have a couple of sets, one surflex and one Barnett, (both sold as compatible with 850), In both cases 4 plates only. Some out there in the big wide world would perhaps suggest 5 fiber plates for the 850?

Anyway, the question is: on an 850 which is better, 4 fiber plates or 5? Or does this question only really apply to bronze type friction plates, (which I think have always been 4 for 750 and 5 for 850)?

Click to expand...

The 850 clutch would normally have 5 friction plates regardless of the type (not all are bronze now), 4 plain and the thin pressure plate.

The 750 clutch (prior to 212278*) would have 4 thicker friction, 3 plain, and thick pressure plate.

You can use the '750' 4-plate clutch in an 850 with the thick pressure plate.
The important thing is that the stack height is correct for the chosen 4 or 5-plate assembly.

*(The 212278-on 750 models had the same 5-friction-plate, thin pressure plate clutch as the 850)

May or may not be your issue, An overfilled gear box and storing the bike on it's sidestand will cause unnecessary migration.

I would remove the CR seal to remove from equation, clean all plates, flat sand the steels, set the height below the circlip.
Set bike level, remove trans level plug and let all excess oil drain, or completely drain it and measure the spec'd amount.
The spec'd amount on mine sits just below my level plug.

Once dialed in, decide whether or not to install CR seal. It's a luxury, not a necessity.

Hi MichaelB:

Thank you for your comments.

Upon checking my gearbox level it actually seemed quite low, maybe 1/4" or a bit more lower than the level plug. It was not that way when I set the level a few weeks ago! The amount migrating through the gearbox main shaft to the primary is quite significant. If I was still running a chain and wet primary I would probably not have known. But with the dry primary / belt drive it is painfully obvious.

I think, certainly with the belt drive, if I want a dry primary, a cr seal is going to be a must for me. Currently have ordered a dynodave type from Colorado Norton Works. But I might also try the new RGM type. After my own experiences I can definitely see why they designed it the way they did.

The following article sounds a lot like at least part of my issue / issues:

http://atlanticgreen.com/rodseal1.htm

Britstuff said:

Hi MichaelB:

Thank you for your comments.

Upon checking my gearbox level it actually seemed quite low, maybe 1/4" or a bit more lower than the level plug. It was not that way when I set the level a few weeks ago! The amount migrating through the gearbox main shaft to the primary is quite significant. If I was still running a chain and wet primary I would probably not have known. But with the dry primary / belt drive it is painfully obvious.

I think, certainly with the belt drive, if I want a dry primary, a cr seal is going to be a must for me. Currently have ordered a dynodave type from Colorado Norton Works. But I might also try the new RGM type. After my own experiences I can definitely see why they designed it the way they did.

The following article sounds a lot like at least part of my issue / issues:

http://atlanticgreen.com/rodseal1.htm

Click to expand...

That is a part of it.

1) use 5 Barnett fiber plates

2) use the stack height recommended by our long standing benefactor referenced in his memoirs.

3) Use the clutch rod seal.

4) Enjoy a slip-proof, non-grabby progressive feal clutch for a LOOOOONG time.

The end.