Revisit the Clutch Stack

swooshdave

swooshdave

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Thread 'Clutch Pull and Clutch Stack Height'

Have we ever had a clutch thread? No? Didn't think so.

Clutch Pull and Clutch Stack Height


So I was getting a little weeping from the primary on my Interstate. No belt drive. Not yet.

When I was in there I noticed a bit of play with the clutch basket. Going the cheapest route I replaced the bearing. That snugged it up a little bit. I really suspect a warn clutch hub center.

Then of course there was the issue with the plates. I remember when I first got the bike I think it had the bronze plates. At some point they were replaced with Barnetts.

Well, they didn't look good.

Clutch Pull and Clutch Stack Height


Now I have new plates in...

Apparently it's been a while, six years?, since I looked at the clutch. The result of all of that work was... nothing.

Time to go at it again. Recently (in the last six years) the club had some thinner clutch plates made by one of the members, since you can't get them from Old Britts anymore. So I'm going to see if I can finally get the stack height right.

Revisit the Clutch Stack
 
Well, I reread my old thread and aside from annoying @dynodave I'm not sure much got accomplished. :p

But there were some tips I'm going to try again.

And as a last resort I can take the clutch stack from my 750 (which I think has the 850 pressure plate, but I honestly can't remember and for some reason I can't find a picture of it disassembled.) and see how it performs on the 850.
 
Well, we have a smoking gun now. And no wonder that messing with the clutch stack height made no perceivable change.

I finally swapped the clutch from the 750 (which was indeed a 750 pressure plate) to the 850 and the easy pull came with it. But then I had an epiphany to just swap the diaphragm springs. And that was it. The 850 spring is the culprit. It's significantly heavier than the one that had been on the 750.

So spring differences can make a... difference. So now the 750 diaphragm is on the 850 clutch stack. And it's a light pull. Once I have the bike back together I'll see if the clutch slips or if it's fine.

And I may try to source another spring and see what that's like.
 
I wonder if people have ever tested a sample size of the springs for their rates? What would a test rig look like?
 
swooshdave said:
I wonder if people have ever tested a sample size of the springs for their rates? What would a test rig look like?
Click to expand...
I think BDM (Mr Leadbeater) had done it ...but I had lost somewhere in my computer all his list !
Matchless

Thread 'Diaphragm spring'

Does anyone know when the diaphragm spring centre design changed. Both my Commandos have the original factory fitted type. For the Atlas I am in the process of building I have just received a spring from RGM & the centre is different to my others. Whilst this doesn't matter to me, there is a problem with this sping, in that when fitted the centre boss will not sit square. I have removed the circlip & pulled it apart but cannot see anything wrong. RGM have said they will send me another but I wonder if anyone else has had this problem.

Martyn.
 
swooshdave said:
I regret reading those JML emails. :oops:
Click to expand...
Here's another for you, "There were 4 different versions of diaphragm spring fitted to Commandos whilst in production."
J

Post in thread 'commando clutch in a P11'

Two different plates? Do you mean diaphragm springs or pressure plates?
There were two different thickness pressure plates The 6mm thick version being for the 5 friction plate later clutch and the 9mm thick version for the earlier 4 friction plate clutch. Both set the deflection point of the diaphragm spring at the same point. IF you alter the deflection point of the spring in any way you alter the load the spring applies to the clutch plates and thus you alter the torque the clutch will transmit before slip occurs...not that the average Commando owner is aware of such facts...
 
So the way to determine the type of spring is to measure the thickness of them?
 
Last edited:
I think he is referring to the pressure plate thickness changing when they went to the later 5 plate clutch.
 
Long ago, I removed the center of a few springs to lighten them, and weighted the naked springs. Iirc, I found a difference of 10 gr between some of them.
 
Well, the spring on the 850 certainly makes for a super light clutch. But I do fear I may be slipping slightly in the top gears. I may need to go with a slightly thinner plate and see if that changes anything.

Maybe a new diaphragm spring just to see what that's like.
 
The UK has a funny drawing system, there is a revision number facility on parts drawings. So the drawing for 06-xxxx will have a box normally down on the right side showing the revision numbers and what changed between revision numbers. So intenally the shop part number would be 06-xxxx rev 3 and the drawing it was inspected to would be 06-xxxx rev 3.

Here is an example where the variations are called alterations. There aren't any in this case but you can see they have left space for many alterations. It was done to cut down on the number of part numbers used taking up computer disc space. When I was in production I wanted each new variation to be a new part number but did not get far. For a flat spring variations in steel thickness would be covered by a new revision number. If @Madnorton has access to the spring drawing he may have more info.

Revisit the Clutch Stack
 
kommando said:
The UK has a funny drawing system, there is a revision number facility on parts drawings. So the drawing for 06-xxxx will have a box normally down on the right side showing the revision numbers and what changed between revision numbers. So intenally the shop part number would be 06-xxxx rev 3 and the drawing it was inspected to would be 06-xxxx rev 3.

Here is an example where the variations are called alterations. There aren't any in this case but you can see they have left space for many alterations. It was done to cut down on the number of part numbers used taking up computer disc space. When I was in production I wanted each new variation to be a new part number but did not get far. For a flat spring variations in steel thickness would be covered by a new revision number. If @Madnorton has access to the spring drawing he may have more info.

Revisit the Clutch Stack
Click to expand...
If each variation had its own part number the MK3 inner chaincase would have over a dozen part numbers.
 
If there were a dozen part numbers then only some of them will have been actually released for production, knowing which ones they were and the engine numbers they were fitted too which make it much easier. The thought of having to start on a fresh piece of paper when changing a part would reduce a lot of these revisions. Remember when you looked at the front wheel and was quoting spoke patterns that never made it into production.

M

Post in thread 'Disk brake front rim dimple pattern'

No from me, but interesting bit of history on the disc wheel.

''Here is the history on the Norton Front Disc wheel.


Norton finished the design of the bike and then came to my father with a hub to build a wheel to fit - due to the fact that they had not considered the wheel in their original design the wheel had to be made with the disc side virtually flat to make it fit the bike - the original wheels were therefore produced with rims with a 1x1 dimple pattern and cross laced to fit and accommodate offset requirement 8 gauge spokes were used on the flat side and 9 gauge on the other for...
 
GM used to do this as well, look up the part number for something and find a descriptor saying "first design" or "second design". An engineering change was made to cure a problem but we dont really know when and where the new one entered the production line so good luck.
 

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