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

Hi:

Does anyone make a higher spring load / heavy duty diaphragm clutch spring for the Norton Commando?

I am having ongoing issues with a slipping clutch on my 1974 850 MKII. I have played extensively with different stack heights, different types of fibre clutch plates, (Surflex and Barnet) and recently fitted a belt drive kit - but my clutch still slips, especially in first at higher revs. While it probably does not help that I live on a fairly steep hill, there must be something I am missing / doing wrong?

I see quite a lot of information on the interweb refering to how to make a Norton Commando Clutch feel lighter. Mine is very light, two fingers or better. However, I would gladly trade a heavier clutch action for a clutch that does not slip!

Cheers,

James

If you have a two finger pull no matter what the stack height was, I'd think the diaphragm spring is weak and replace it with a new one. If the stack height is wrong you will NOT pull it with two fingers. It's possible someone left the spring compressed for a period of time, weakening the spring but looking new. IMHO

Hi Gene:

Thank you for your comment. Two fingers is indeed the heaviest I have encountered, regardless of stack height. This is my first Commando and the clutch slipped when I bought it, so I am definitely lacking experience on what is normal.

Somehow I have managed to accumulate three different diaphragm springs, all of which feel about the same and the clutch still slips. They could all be bad, sods law suggests it be so. It would certainly explain my continuing issues.

Cheers,

James

If you have gone to a belt drive (no fluid in case) from a chain and it still slips then that it very unusual.

Another possibility is you are setting the adjuster on the clutch pushrod with too little free play. Have you tried backing it off another half turn maybe.

Hi John:

Thank you for your comment. I went to the belt drive (no fluid in case) hoping it would solve my problems, but apparently not. Although I'm pretty sure I am going to stick with it as it seems to be a very well made piece of kit and the belt appears to run straight and true.

Been playing around with the adjuster every which way I can think of, (i.e. first fully slacken the control cable, tried 1/2 / 1 / 1 1/2 turns from stop, then take up slack) and have made a point of making sure I have way more slack / free play than I should need. I do not think that is my problem. I also have a Dominator and an AJS with the same adjusters and have no problems setting the adjusters on those. That said, the amount of stuff I have tried, it sure feels like I am doing something wrong. I Just have not found out what it is yet!

Cheers,

James

Britstuff said:

Two fingers is indeed the heaviest I have encountered, regardless of stack height.

Click to expand...

Did you make a note of the various stack height measurements?

I also don't know how you could have lowered the stack height without the clutch action feeling noticeably heavier unless it was abnormally high, to begin with.

Hi L.A.B:

Thank you for your comments.

Regrettably I did not record stack height adjustments. All I can say is I have had it so low the diaphragm spring is no longer convex / is flat and will not open cleanly as the pressure is no longer centered. Also all the way to the point that I can only just install the clutch spring retaining circlip and cannot get the clutch plates to break apart at all when the clutch lever is depressed. That and most every place in between with the aid of three different thicknesses of pressure plate!

I can honestly say, that through all of this, I have never felt the clutch became noticeably heavy. It does seem that this is significant. My Commando clutch is much lighter than my AJS, a bit lighter than my Dominator. It it is the lightest clutch I can remember having since I sold my Hinckley Bonneville some years back.

Kind Regards,

James

it sounds like you might have the thicker 750 friction plates. the giveaway was when you stated surflex. we need more info as to how thick the friction plates measure and how many along how many steel plates and thickness. the spring should be slightly concave. the closer to flat the less holding power the spring has but also the more concave it is the more holding power it has along with the harder it is to release. the stackup highth is a fine line as to easy pull vs slipping. take it apart and come back with measurements of the parts

Here is a steaming pile of advice you could probably do without:

I'm probably using a different belt clutch, but I back all the adjusters off. Then turn the one on the clutch in until it just touches the clutch push rod with no slack. Then back it out one full turn or slightly less. Once that is done, set your bar lever adjustment at the bar lever, or set it at the adjuster at the gearbox to get your lever adjustment. Either work, but I find it better to get the type at the gearbox up further away from the pushrod actuating lever. I set my lever at 1/4" of slack, but I am using Magura levers that pull a long way. If I set the adjuster at the clutch at 1/2 turn back my clutch does not work that well. It does not slip, but it takes way too long to re-engage and I end up slipping the clutch during launch. Annoying for me. Especially with a new clutch. At 1 turn out it's on the money for me. You may or may not like it.

If the Dominator and AJS have AMC 3 spring clutches in them, they will be noticeably heavier at the lever than your belt clutch. If they have belt clutches in them with diaphragm springs and are the same belt clutch that you have in the Commando, measure the stack in those clutches and duplicate it in your Commando belt clutch.

I often get stuck in an endless trouble shooting loop. After about the 7th try, the light bulb lights up and I have a solution. You'll get there.

The stack height on my belt clutch was figured out by RGM. Even though I complain a little about RGM, it is ideal with the proper clutch adjustment. I have not messed with the stack height, nor do I know what it actually is. The spring has to be very compressed to get it in.

Thank you Bill and Schwany. I think my next step is going to be to approach the manufacturer of the belt drive to verify the recommended stack height. What I have should be correct, (plates: plain, fibre (surflex) and pressure were supplied with the belt drive) but I think I will check.

I think that stack height is not the core problem, although that may well be adding to my issues. Anyway, verifying the recommend stack height sounds like a good way to reduce the variables. I think I might also try a new spring diaphragm. Sounds like nobody sells a high pressure diaphragm. So maybe I will just try one from a different supplier. It seems to me what is the most striking takeaway from everyone's feedback is that my clutch should, (at least under some circumstances) feel heavier than it does, which makes me think maybe the pressure applied by my current suite of clutch diaphragms is insufficient.

FYI. the AJS and Dominator do both have good old three spring clutches. Both are easy to mess with, easy to setup and actually work! I think the reason the AJS is heavier than the Dominator is primarily down to lever type fitted and their different geometry / fulcrum's.

I regret I am way past my 7th try, but at least with the belt drive, trying new configurations is a lot easier, and way less messy!

Come to me, oh sweet light bulb of wisdom!!!!! :<)

Have you checked condition of the clutch actuating lever and ball bearing inside the gearbox? When I had my 850 gb apart for all bearing/bush replacements, the actuating lever was badly worn out of shape. Have also heard Mick Hemings on his gb DVD state he's seen the clutch rod become welded to the ball bearing due to no slack set on the adjuster. I recall an old thread on this forum discussing using an actuator lever from a different model Norton with different pivot point/angles giving easier clutch pull. Perhaps you have an odd one?

For reference, I measured my stock clutch force at bar lever to be around 27 lbs to pull to bar. Then fit a 3mm solid plate from RGM in place of one stock thinner plate, got around 15 lbs pull force. A 4mm plate gave around 8 lbs but I found slippage at higher torque demand situation. Now run the 3mm plate, never any slip felt.

Britstuff said:

All I can say is I have had it so low the diaphragm spring is no longer convex / is flat...

Click to expand...

Under normal circumstances, the outer face of the spring would not be "convex" as you look at it, with the clutch 'engaged' (lever released) unless the stack height was 'high'.

With the stack 'normal' (or 'low') the spring would certainly begin from concave (the "Clutch Fully Home" line) and may pass through flat to convex as it is lifted (to the "Clutch At Full Lift" line).
Lowering the stack height moves the positions of the lines equally along the "Diaphragm Spring" curve to the left (increasing the spring "Clamping Force").
Increasing the stack height moves the lines to the right, therefore, decreasing the clamping force and also reducing the clutch 'pull'.

Britstuff said:

...and will not open cleanly as the pressure is no longer centered.

Click to expand...

I don't understand what you mean. Please explain because the (spring?) pressure shouldn't somehow be moving off-centre or lifting unevenly from the pressure plate.

Britstuff said:

Also all the way to the point that I can only just install the clutch spring retaining circlip...

Click to expand...

Difficulty inserting the circlip can only be due to the stack height being too high.

The picture shows the stack height 'low'. The spring is well clear of the groove so does not obstruct the fitting of the circlip.

Britstuff said:

...and cannot get the clutch plates to break apart at all when the clutch lever is depressed.

Click to expand...

When the clutch is disengaged (lever pulled to the grip), only the spring is lifted by the mechanism. Whether the stack height is 'high' or 'low' the amount of spring lift shouldn't change.

Random questions:

Have you checked the plain plates for warping?
Is the operating lever correctly seated against the ball bearing?
Is there any evidence of the diaphragm/adjuster screw fouling anything (clutch hub, mainshaft etc)?
Is the clutch assembly correctly retained on the mainshaft via the thrust collar & circlip?

LAB i have found on a replacement diaphragm spring that was supplied to me that the fingers were NOT stagggerd in the center like the original ones. This diaphragm would not give an evan lift. I hope the OP comes back with the info i saked for till than it a guessing game but the stack up is to tall. Also i have had issues with the RGM belt basket where i had to open up the snap ring groove for the diaphragm spring

bill said:

LAB i have found on a replacement diaphragm spring that was supplied to me that the fingers were NOT stagggerd in the center like the original ones.

Click to expand...

Yes, the latest replacement diaphragm springs do not have staggered fingers...
...and have been manufactured that way for some years now (including the one in the OldBritts stack height picture in my previous post).

Perhaps unlikely that all three of Britstuff's diaphragm springs are of the latest type.

bill said:

LAB i have found on a replacement diaphragm spring that was supplied to me that the fingers were NOT stagggerd in the center like the original ones. This diaphragm would not give an evan lift. I hope the OP comes back with the info i saked for till than it a guessing game but the stack up is to tall. Also i have had issues with the RGM belt basket where i had to open up the snap ring groove for the diaphragm spring

Click to expand...

Those fingers not being staggered is a huge fail.
It is an integral part of the design & function of the clutch.

concours said:

Those fingers not being staggered is a huge fail.
It is an integral part of the design & function of the clutch.

Click to expand...

Not according to the late JM Leadbeater (Beltdriveman). According to him, the slots were staggered to prevent chatter and wear.
"18
.
However, JUST in case it is of interest to anyone the ONLY reason for the 40 thou offset to the piercings in the Laycock Eng. (Haussermann) release ring is as follows: The piercings in the release ring require to be larger than the hardened ends of the release ears so as to fit them into the release ring. If the piercings were all in line then the release ring would vibrate on the ears resulting in VERY QUICK WEAR AND FAILURE..."

As previously mentioned, the design was changed several years ago. If there was a problem with the design then I'm sure it wouldn't have continued to be made that way for very long.

L.A.B. said:

Not according to the late JM Leadbeater (Beltdriveman). According to him, the slots were staggered to prevent chatter and wear.

Norton Clutch

"18
.
However, JUST in case it is of interest to anyone the ONLY reason for the 40 thou offset to the piercings in the Laycock Eng. (Haussermann) release ring is as follows: The piercings in the release ring require to be larger than the hardened ends of the release ears so as to fit them into the release ring. If the piercings were all in line then the release ring would vibrate on the ears resulting in VERY QUICK WEAR AND FAILURE..."

As previously mentioned, the design was changed several years ago. If there was a problem with the design then I'm sure it wouldn't have continued to be made that way for very long.

Click to expand...

I don't agree with leadbeater on that point.

concours said:

I don't agree with leadbeater on that point.

Click to expand...

Then please explain why not.

L.A.B. said:

Then please explain why not.

Click to expand...

I will, inabit, when I'm done this mess