Clutch Pull and Clutch Stack Height

I once cured a heavy clutch pull by changing the operating lever, night and day difference. I then made it hydraulic and it got even lighter, one finger operation now.

The lever that was in there (on the right) looks to be stamped or cut and then the cable end was formed, maybe by stamping.

This is a quite the contrast to the AN part which is cast.



What was even more surprising was the shape. I didn't expect it to be so different. The AN part is on the top. I am assuming the steep ramp of the level that was in there may have been contributing to the stiff pull.



The roller was exactly the same size. I will just keep the old one as a spare, although I suspect they don't wear a lot.

I got it all re-assembled but I was held up from testing the pull by my outer cover.

swooshdave said:

The roller was exactly the same size. I will just keep the old one as a spare, although I suspect they don't wear a lot.

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When I was doing my resto-mod, I took this pic of a bunch of parts that needed replacing (sorry for the crummy pic- it was in a ziploc) and you can clearly see the roller is lobed.

There was other strange stuff inside my tranny, too.

swooshdave said:

The lever that was in there (on the right) looks to be stamped or cut and then the cable end was formed, maybe by stamping.

This is a quite the contrast to the AN part which is cast.

What was even more surprising was the shape. I didn't expect it to be so different. The AN part is on the top. I am assuming the steep ramp of the level that was in there may have been contributing to the stiff pull.

The roller was exactly the same size. I will just keep the old one as a spare, although I suspect they don't wear a lot.

I got it all re-assembled but I was held up from testing the pull by my outer cover.

Kickstart Shaft Seal Tutorial

I don't recall what seal I used when I rebuilt the gearbox on my 750. I think I just used an O-ring. https://www.accessnorton.com/NortonCommando/gearbox-teardown-with-plenty-of-pictures.5107/post-53593 The 850 is definitely leaking and it's got an O-ring. I picked up some SKF 9815 (actually not...

www.accessnorton.com

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Pretty much the same as mine.
I wonder if this may be a substantial cause of the heavy clutch. If you look at the old one on the wearing surface you can see how shiny and polished it is. I suspect that years of vibration with a heavy load causes the roller to wear away into the actuator, causing the pivot point to be in a disadvantageous position.
When I first looked at mine, the wheel fitted the actuator so well that from an engineering point of view it seemed “correct”. I wouldn’t be surprised if others had felt the same and decided it didn’t need replacing!

swooshdave said:

The lever that was in there (on the right) looks to be stamped or cut and then the cable end was formed, maybe by stamping. This is a quite the contrast to the AN part which is cast.
What was even more surprising was the shape. I didn't expect it to be so different. The AN part is on the top. I am assuming the steep ramp of the level that was in there may have been contributing to the stiff pull.

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The original release arms were stamped out of stock easily detected on the undressed portions, The ballsocket and lift profile are ground.
The lift profiles may have varies as time went on which was the cause for the super stiff "ziggy" arm.

The new NA is very likely PM powdered metal and will likely be very consistant to the die it is made in. That is why no holes are present...
Scaling off your pix:
There is likely a 5.3% leverage improvement at the base of the lift profile where the improvement is needed the most = fingers outstretched.
The lift advantage appears to then reduce to 3.1%, over the original release arm, since closed fingers are stronger against the clutch lever.
Without doing a complete assembly measurement I can only guess there may also be a slight reduce overall lift as it was not really necessary in the original.

Ok, were are we? Ah, yes finished up with the kickstart shaft seal.


Now back to the clutch.

So I tried it again now with the old clutch cable. Still pretty stiff. Let's look at the new cable.



Pretty much no drag.

So new cable needs to go in. You know what this means.

New cable when in. Of course it wouldn't just drop in. The ball at the gearbox end was too big to fit in the hole. So I had to file it down a little.

Clutch stil stiff. Back to the stack height.

I eventually ended up at 1.242" (Five new Barnett plates and 5 steel plates) and I'm definitely better although still not at a two finger clutch.

If you recall my basket depth is 1.135" not that it apparently matters too much yet.

I'm starting to feel the over center sensation. I think a little more stack height might do it. But for now I'll just wait until I get belt drive before going back in there. I will need to test it briefly before putting oil in the primary to confirm I'm not slipping.

Next up is getting the primary chain tension, rear chain tension and maybe finally take it for a real ride.

I was bitten by the old oversize ball on my new cable also a while back..... Frustrating thing to pull it out and then fish it back through.

I had the same thing happen with the new Venhill cable I got a couple years ago. Maybe somebody should let them know.

swooshdave said:

I eventually ended up at 1.242" (Five new Barnett plates and 5 steel plates) and I'm definitely better although still not at a two finger clutch.

If you recall my basket depth is 1.135" not that it apparently matters too much yet.

I'm starting to feel the over center sensation. I think a little more stack height might do it.

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For the spring to be anywhere approaching 'flat' then the stack height plus the spring* needs to be approximately equal to the drum dimension from the backplate to the circlip groove.

*(According to BDM's notes "The springs I found in Commando clutches and have had tested were approximately 0.075, 0.078/9, 0.080/1, 0.082 and 0.084 inch thick.")

The section of spring between the thrust ring of the pressure plate and the outer edge is what needs to be set 'flat', not the release fingers.

swooshdave said:

I'm starting to feel the over center sensation. I think a little more stack height might do it.

Click to expand...

If 1.135" is the drum spline depth then that is approximately 0.150" short of the actual drum depth dimension which is to the circlip groove when the stack height is measured to the thrust ring of the pressure plate and which would make the drum depth approx. 1.285".

With a stack height of 1.242" plus the spring (approx. 0.080") that would already seem to make the stack about 0.037" 'high'.

L.A.B. said:

For the spring to be anywhere approaching 'flat' then the stack height plus the spring* needs to be approximately equal to the drum dimension from the backplate to the circlip groove.

*(According to BDM's notes "The springs I found in Commando clutches and have had tested were approximately 0.075, 0.078/9, 0.080/1, 0.082 and 0.084 inch thick.")

The section of spring between the thrust ring of the pressure plate and the outer edge is what needs to be set 'flat', not the release fingers.




If 1.135" is the drum spline depth then that is approximately 0.150" short of the actual drum depth dimension which is to the circlip groove when the stack height is measured to the thrust ring of the pressure plate and which would make the drum depth approx. 1.285".

With a stack height of 1.242" plus the spring (approx. 0.080") that would already seem to make the stack about 0.037" 'high'.

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Well, I tried it lower and it felt worse, so in the end it’s better than it was before. If it doesn’t slip then I’ll declare victory and ride.

Where did the stack height/basket depth (to groove) end up on your bike?

swooshdave said:

Well, I tried it lower and it felt worse, so in the end it’s better than it was before. If it doesn’t slip then I’ll declare victory and ride.

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Yes, indeed.

swooshdave said:

Where did the stack height/basket depth (to groove) end up on your bike?

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I have no measurements written down but only remember when I did the OldBritts (spring to circlip groove) measurement quite some time ago that the stack height was significantly 'low' although the clutch pull was a little heavy it wasn't a problem and the over-centre position was close to the handlebar grip.
This was the standard 5-bronze friction plate clutch.
About a year ago (or could be nearer two?) I installed a set of Surflex (5-plate clutch) fibre plates (just because!) and which, if I remember correctly increased the stack height only slightly, once again I don't remember by exactly how much as I wasn't aware I might be 'asked questions later'.
Earlier this year (as something to do during lockdown) I replaced one standard plain plate with the RGM 3.0mm (+0.040") plate which moved the O/C to approximately the mid-lever position and noticeably lightened clutch lever action.

Although the stack height is apparently still a little 'below flat' the lever action is light enough (as hopefully demonstrated in my previous video?).
As the next (and only?) thickness plain plate readily available is the RGM 4.0mm which might be too much so I'm content to leave things as they are for the time being.