Clutch Pull and Clutch Stack Height

dynodave said:

In this case SD is correct. The top of the splines except for a few thou IS the where the bottom of the diaphragm sits and that is "almost" the clutch BASKET height.

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Yes, I would agree it is "almost"!

Edit: According to BDM's notes regarding the thickness of Commando diaphragm springs the measurement to the top of the splines could be 'low' by approximately 0.070" - 0.080".

dynodave said:

The diaphragm edge does not move from that position.

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Yes, I know.

dynodave said:

clutch basket is a different and seperate part of the clutch than the clutch plate stack.
Thrust ring is part of the clutch pack/stack!

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Obviously.

dynodave said:

The only other option is to measure from the TOP of the circlip groove and subtract the circlip thickness and subtract the diaphragm thickness to get a slightly more accurate clutch basket height

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Not the only option.
A far easier way in my opinion (and without having to go 'all around the houses' with measurements to get there):
(Drawing not to scale)


Edit: It's basically the same as the OldBritts procedure except that OldBritts measure with a rule.

L.A.B. said:

Not the only option.
A far easier way in my opinion (and without having to go all the way around the houses with measurements to get there):
(Drawing not to scale)
View attachment 17593

Edit: It's basically the same as the OldBritts procedure except that OldBritts measure stack height differently.

Old Britts, Commando Clutch Plate Information

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I'm hypothesizing here.

The procedure becomes:

1. Set diaphragm flat using the spring compressor. Confirm using a straight edge.
2. Put the clutch pack in.
3. Put the diaphragm spring in.
4. If the diaphragm spring top is even with the circlip groove then you should be in "flat" condition when you release the compressor.
5. If the diaphragm spring is below the circlip grove you will be in a concave condition (when you release the spring, assuming the circlip in place) the center of the spring will move in, and the edge of the spring will rise to the circlip.
6. If the diaphragm spring is above the circlip groove, depending as long as it's not too much, you can still install the circlip by taking the spring from flat to concave (dished out) as long as there is room between the edge of the pressure plate and the bottom of the circlip groove. This puts you in a concave (dished out) condition (and according to @dynodave's chart in danger of not having enough clamping force, although the lever feel should be light).

Then it becomes a matter not of measuring the stack heigh as much as the relationship between the top of the spring edge and the bottom of the circlip groove. As per Old Britts.

This is in line with what @comnoz mentioned in a previous thread about aiming for a flat spring.

On my 750 I'm a little convex (dished in) and find the level feel really good, and potentially shimming to a flat condition might improve it slightly. I have not measured where exactly I am below the bottom of the circlip groove on the 750.

Unfortunately, mentioned, there was no condition on the 850 that worked and I tried all the options. But it gave me good experience as to what the possibilities are.

To validate the above I'd need to take my 750 (because I believe it has a good actuator mechanism) and adjust the stack until I got an undesirable lever feel and report back the location of the diaphragm spring in relationship to the bottom of the circlip groove.

Unless someone wants to test their bike first.

The previous cable on my bike was in good shape and lubricated . Just switching to a Venhills Featherlight cable reduced pull on the clutch lever by 1/3 as measured with a spring scale.

Glen

swooshdave said:

I'm hypothesizing here.

The procedure becomes:

1. Set diaphragm flat using the spring compressor. Confirm using a straight edge.
2. Put the clutch pack in.
3. Put the diaphragm spring in.
4. If the diaphragm spring top is even with the circlip groove then you should be in "flat" condition when you release the compressor.
5. If the diaphragm spring is below the circlip grove you will be in a concave condition (when you release the spring, assuming the circlip in place) the center of the spring will move in, and the edge of the spring will rise to the circlip.
6. If the diaphragm spring is above the circlip groove, depending as long as it's not too much, you can still install the circlip by taking the spring from flat to concave (dished out) as long as there is room between the edge of the pressure plate and the bottom of the circlip groove. This puts you in a concave (dished out) condition (and according to @dynodave's chart in danger of not having enough clamping force, although the lever feel should be light).

Then it becomes a matter not of measuring the stack heigh as much as the relationship between the top of the spring edge and the bottom of the circlip groove. As per Old Britts.

This is in line with what @comnoz mentioned in a previous thread about aiming for a flat spring.

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Yes.

swooshdave said:

On my 750 I'm a little convex (dished in) and find the level feel really good, and potentially shimming to a flat condition might improve it slightly. I have not measured where exactly I am below the bottom of the circlip groove on the 750.

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It's possible that increasing the stack height could improve it further. It might be worth a try and you can always put it back to how it was if it begins slipping.

swooshdave said:

Unfortunately, mentioned, there was no condition on the 850 that worked and I tried all the options. But it gave me good experience as to what the possibilities are.

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The '850' clutch shouldn't be heavy when set correctly although it's possible the '850' spring could be stiffer than the 750 spring (as the stiffness of the diaphragm spring was apparently increased-twice, although there was no change of part number)?

As you seem to have already tried various combinations of plates/stack heights without any significant improvement then I also suggest you fit a new cable and check the actuator arm parts (and that it hasn't dropped out of position?)

L.A.B. said:

The '850' clutch shouldn't be heavy when set correctly although it's possible the '850' spring could be stiffer than the 750 spring (as the stiffness of the diaphragm spring was apparently increased-twice, athough there was no change of part number)?

As you seem to have already tried various combinations of plates/stack heights without any significant improvement then I also suggest you fit a new cable and check the actuator arm parts (and that it hasn't dropped out of position?)

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New cable and actuator parts just ordered from Old Britts, as mentioned previously that was the plan after seeing that nothing was improving the clutch. I should have them in a couple days. If that actually works I may just ride the dang bike up to Old Britts, although they don't take visitors...

worntorn said:

Swoosh once stated his disappointment at my general lack of knowledge on clutches.
He was surprised to learn ..."That you didn't understand how the non-diaphragm clutches work. :|"

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Mental note that @worntorn will hold a grudge, seemingly forever.

I will need to look up the original quote and see just how long ago that was.

Truth is, you were correct, I really don't understand exactly how clutches work.
I'm very relieved when they do.

Glen

swooshdave said:

New cable and actuator parts just ordered from Old Britts, as mentioned previously that was the plan after seeing that nothing was improving the clutch.

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My 850 with five Surflex fibre friction plates, three standard plain plates, one RGM 3mm plain plate and Venhill cable for comparison.
The 3mm (+1.0mm) plate was a definite improvement. The stack is approximately 0.020" 'low' but is light enough for me:

That's just plain as day cheating....... I don't guess I should complain because my 850 and GL 1000 feel about the same on pull.... Maybe I'm just getting old and aching and bitching makes me feel better. So I withdraw any gripes I may have mentioned about clutch pull on my Norton.

Yep... just walked out and pulled both. No diff. Too much booze & smoke in my youth.

jbruney said:

That's just plain as day cheating....... I don't guess I should complain because my 850 and GL 1000 feel about the same on pull.... Maybe I'm just getting old and aching and bitching makes me feel better. So I withdraw any gripes I may have mentioned about clutch pull on my Norton.

Yep... just walked out and pulled both. No diff. Too much booze & smoke in my youth.

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So are they good or bad?

I'll put it this way... I rode the wing for years whilst the Norton was stored swearing it had the smoothest clutch I'd ever felt. Now with both going I've come to realize I had no idea what I was talking about.... They're both stout, although not unreasonably so with the Norton being a fast grabber. One is like a sports car and the other reminds me of the old John Deere tractors on takeoffs. Just my take on things. At least you're not pulling a motor to work on a Commando clutch so life is good.

jbruney said:

I'll put it this way... I rode the wing for years whilst the Norton was stored swearing it had the smoothest clutch I'd ever felt. Now with both going I've come to realize I had no idea what I was talking about.... They're both stout, although not unreasonably so with the Norton being a fast grabber. One is like a sports car and the other reminds me of the old John Deere tractors on takeoffs. Just my take on things. At least you're not pulling a motor to work on a Commando clutch so life is good.

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Well, we're going to find out this week if I can get my bike sorted and what it will take. Maybe you can take a swing at your bike next.

How many miles on your bike? Wet or dry primary? Have you been into the primary before?

How much variation in stackup have you been able to achieve with your plate swapping? My non scientific seat of the pants opinion is that if you don't feel the spring snap over center then you haven't added enough to the stackup.

maylar said:

if you don't feel the spring snap over center then you haven't added enough to the stackup.

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Or the spring is already over-centre (or flat).

swooshdave said:

Dave says to have it slightly inverted (bowed out). Comstock said he likes his flat. And on my 750 it bows in and feels great.

If there was one right answer there wouldn’t be a need for more questions.

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Easy to see how perceptions and my lack of excruciating detail in my articles can let folks think they understand!
Not intimately knowing the main characteristics of the degressive-negative-progressive diaphragm can lead one to only very minimally or not at all understand what is happening. I just this morning re-reviewed the hasserman diaphragm article and can see how easily one can get way off track.

I am pretty sure I can now see why I could not detetect different rate diaphragms. Not that I tried all that hard...I do not believe thickness (t) was changed. It was "ho".
Further review of the engineers description (math) of the diaphragm, I believe can see clearer why my perceptions had short comings as do others perceptions.

In general what folks think is "flat"...is not. The basket depth VS stack height precision required has very serious result differences. Hand grenade accuracy will get you hand grenade results.
Looking at SD two pix with the white arrows may have been similar to my 23 year old perception but a bit off the mark.
Flat is derived by a load measurement like in my chart and NOT a straight edge across the disengagement fingers.

thin PP thrust ring height is .11"
thick PP thrust ring height is .122"

Mine is at 24K and the clutch is just reworked with better mic'ing disc & plates, also a somewhat more resistant spring/slightly longer engaging rod making it not slip & it snaps over more easily.... I also increased the height a bit through all of these piddling gestures, but just by a bit.... The beast is by far more tame than the one it was hatched with. Very pleased unless the arthritis worsens.

dynodave said:

In general what folks think is "flat"...is not. The basket depth VS stack height precision required has very serious result differences. Hand grenade accuracy will get you hand grenade results.

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Except when I asked you about the relationship between basket depth and stack height you said, and I quote, "The correct height is your choice..." So which is it, precision or a choice?

Also you missed the point about my experimenting (or as you call it, hand grenading) as that was to demonstrate that despite a variety of stack heights there was no discernible difference which points to an issue elsewhere. We'll know later this week if that assumption is correct.

I feel there some information out there about both a technical and practical approach to the Norton clutch. But I think there is still a gap.

The spring pressure chart is great but it's not the complete picture. To develop this out further more can be done. I feel there should be a mapping between the spring pressure, lift height, stack height (in relationship to the basket depth) AND lever pull weight. That is, in my opinion, the scientific way to finally answer all of the questions. Thanks to @dynodave we have several of the variables understood already. It's just a matter of filling in the rest.


From a practical standpoint I think my proposed approach still seem sound and I'll attempt to prove it out at some point:

1. Set diaphragm flat using the spring compressor. Confirm using a straight edge.
2. Put the clutch pack in.
3. Put the diaphragm spring in.
4. If the diaphragm spring top is even with the circlip groove then you should be in "flat" condition when you release the compressor.
5. If the diaphragm spring is below the circlip grove you will be in a concave condition (when you release the spring, assuming the circlip in place) the center of the spring will move in, and the edge of the spring will rise to the circlip.
6. If the diaphragm spring is above the circlip groove, depending as long as it's not too much, you can still install the circlip by taking the spring from flat to concave (dished out) as long as there is room between the edge of the pressure plate and the bottom of the circlip groove. This puts you in a concave (dished out) condition (and according to @dynodave's chart in danger of not having enough clamping force, although the lever feel should be light).

Ok, parts from Old Britts should be here tomorrow.

I took apart the gearbox cover in anticipation.







Plastic spudger to prevent marring the gearbox.



So @SteveC, is this what yours looked like?



I can't wait to compare it to a new AN one. Although from a practical standpoint one would assume that a few thousandths on the actuator wouldn't matter as it doesn't seem like that should affect the lift that much. But the shape could definitely have an effect on the feel.

Cover is ready to go on, but still need to wait for the parts. I should do the kickstart shaft seal too, if I can find one locally. If not I'l do it later.

For the record when I measure the stack height dry it was 1.125"
After I soaked the plates in ATF they must have swelled as the the new height is now 1.158"
And the basket depth is 1.135"

Yes, pretty much exactly as mine was.
With the new one from AN, the wheel was sitting on a curve, so that the pivot point could vary slightly as the cable was pulled.
Interested to see pics of your new part.