Clutch Pull and Clutch Stack Height

I did see the RGM plates. I’m going to borrow some more plates and a different spring just to see if there’s any difference. I’m also going to take a closer look at the cable.

I’m hesitant to over invest right now as I’ll going to put in a belt drive at some point and may need to do it all over again.

I tried a different spring. No difference.



I'm keeping track of the different stack heights. I have a mix of new 850 Barnett plates, some used Barnett 750 plates (thicker), and even some old fiber plates. Mixing and matching just to get different stack heights and see if anything feels good. To be honest the one combination that didn't suck horrible was three 850, two 750 and four steel plates. That felt like I was almost getting an over center. But it was still stiff. That was at 1.1205" A smidge either side of that was bad.

If you click on the video below you can see the cable action. I think it's not bad. Nothing is binding. Feels smooth.



I am getting REALLY good at taking plates out.

Given the range of heights I've tried with no discernible difference makes me think the actuator might actually be the culprit.

I got a reasonable action with 1.08”. Not quite two finger but not tiring like it used to be. I felt I could go up a bit but wanted to check for clutch slip first.
Have you checked by feel that the clutch actuator isn’t adding any friction. The slightest graunchiness (I’m English so I am allowed to use words like this) is really amplified by the weight of the clutch spring.

SteveC said:

I got a reasonable action with 1.08”. Not quite two finger but not tiring like it used to be. I felt I could go up a bit but wanted to check for clutch slip first.
Have you checked by feel that the clutch actuator isn’t adding any friction. The slightest graunchiness (I’m English so I am allowed to use words like this) is really amplified by the weight of the clutch spring.

Click to expand...

The clutch actuator is my next target, I already greased it up good and that made no difference at all. With as many miles that are on this bike I could see it wearing, especially since it's always had a stiff clutch. I'm wondering if the roller also would wear.

With 1.08" is that 750 or 850?

If you are looking for some "magic" transformation, you may be disappointed.
Analysis by another person requires data disclosure.
What is the clutch basket depth? Without out this NO relationship to a FLAT clutch diaphragm can be established. So it's like you are just throwing darts at a board you can't see.

1. The clutch lever feel and ease of operation responds at a cosine rate ( 10-15 degrees worth) and becomes easier by a few percent as the lever reaches the bar.
2. The human hand strength ergonomics makes the lever seem easier as you aproach a closed fist grip.
3. skipping the cable friction issue for now
4 The clutch actuator it very relevant. The ease of the roller movement and the correct size(1/2") ball bearing. A linear ramp vs a decreasing lift ramp will affect the feel greatly.
The shape is not easy to decipher as a linear lift is a curve around the center of the ball bearing and the action is effected at the "roller".

I had helped "ziggy" RIP in the pittsburg area where his belt drive was brutally hard and was not getting any help from Bob Oswald of Quiet Power Drive in Pennsylvania. (BDM hero) !

The original profile of actuator #3 gave ziggy approximately a 25-30% harder lift than normal(commando). I modified his actuator into a normal atlas profile and it was completely transformed.

The clutch pull looks to have been a concern at the factory too, they changed the fulcrum point at the lever mount. They did not change the fulcrum radius but moved the point and the clutch lever inwards so if you kept you hand on the handlebar grip in the same position your hand landed on the lever further outwards increasing the leverage. This photo shows a 72 at the back and 74 clutch lever mount on the switch gear. If you moved your hand inwards by the same amount then there was no difference.

dynodave said:

What is the clutch basket depth? Without out this NO relationship to a FLAT clutch diaphragm can be established. So it's like you are just throwing darts at a board you can't see.

Click to expand...

Can you clarify where you measure the clutch basket depth at? Back of the basket to the end of the grooves? To the circlip groove?

This is not rocket science...
where does the BOTTOM of the clutch stack go? answer... bottom of the clutch basket! That steel plate held by the rivets.

Where does the TOP of the clutch stack go? answer... The thrust ring on the pressure plate thrusts/contacts on the back of the diaphragm. (this is why old brits stack height is IMO STUPID)
THE WHOLE POINT to setting the shape of the diaphragm is the height difference of the thrust ring to the back side seated position of the diaphragm OD edge at the top of the splines. "top of the splines is the other end of the clutch basket depth" where the diaphragm sits.... below the circlip.... further below the diaphragm
The difference results in concave if stack is short-flat if stack is equal-convex if stack is taller than the CLUTCH BASKET DEPTH
A clutch basket can be modified there for the basket depth is not a constant and MUST be measured
The clutch stack can be modified therefore the stack height must be measured.
The individual diaphragm pressure curve is FIXED
The diaphragm pressure/position is entirely dependent and set by the relationship of the basket depth VS the stack height.

As bizzare as it sounds, setting up the clutch in valve spring terms.
Make believe you want to set the valve spring seating pressure tp 96lbs. seating pressure is currently too light. For a valve you "magically" make the stem shorter and the seating pressure goes up.

In this clutch the stack height shorter makes it stiffer. not magic

dynodave said:

The diaphragm pressure/position is entirely dependent and set by the relationship of the basket depth VS the stack height.

Click to expand...

Ok, we can get the basket depth and we can adjust the stack height. Those are the simple parts.

What is missing is any indication as to what the relationship between the basket depth and the stack height should be. Is it a fixed measurement or a ratio? Is there a formula?

Let's say hypothetically the basket depth is 1" (measured from the steel plate at the bottom of the basket and to the top of the splines). What is the correct clutch stack height?

swooshdave said:

The clutch actuator is my next target, I already greased it up good and that made no difference at all. With as many miles that are on this bike I could see it wearing, especially since it's always had a stiff clutch. I'm wondering if the roller also would wear.

With 1.08" is that 750 or 850?

Click to expand...

1.08“ was on my 750. I replaced arm and roller and ball bearing.
when I compared with new the roller did t show much loss, but the arm had worn considerably .

swooshdave said:

Ok, we can get the basket depth and we can adjust the stack height. Those are the simple parts.
What is missing is any indication as to what the relationship between the basket depth and the stack height should be. Is it a fixed measurement or a ratio? Is there a formula?
Let's say hypothetically the basket depth is 1" (measured from the steel plate at the bottom of the basket and to the top of the splines). What is the correct clutch stack height?

Click to expand...

The correct height is your choice...think of your diaphragm as floating in space. The ONLY way to make use of an unreferenced item (diaphragm) is to use the FLAT reference you to pick concave- stiffer left of flat...or you pick FLAT on chart... or you pick softer convex to the right of flat.
Flat is when the stack height is the same as the clutch basket depth.
stiffer is harder to pull and too soft and may slip
Flat is about 210lbs at the diaphragm center and about 420 at the thrust ring on the pressure plate. 420 would be the clamping pressure on the clutch and friction plates
you want more? you want less?

A coil spring clutch used to be the extremely uneducated perception of how this clutch worked.
This chart allows you to know what you are doing in an entirely different way....that at first I got a mild pat on the back by BDM for showing the correct relationship then he later got nasty
Back in 1997 this concept was NOT well known to the norton public though not a secret...there fore my 10 minute test followed by a write up that he did not like.
here if you want to see his: enjoy!
http://a20b767e.magix.net/#xl_xr_page_1

dynodave said:

The correct height is your choice...think of your diaphragm as floating in space. The ONLY way to make use of an unreferenced item (diaphragm) is to use the FLAT reference you to pick concave- stiffer left of flat...or you pick FLAT on chart... or you pick softer convex to the right of flat.

Click to expand...

So to reiterate:

1. Measure the basket depth (BD) (from backing plate, the one riveted in) to the top of the splines.
2. Measure the clutch stack height (CS). This is from the bottom plate to the top of the pressure plate (I believe you called it the thrust ring).
3. If they are the same then you should have a flat diaphragm. BD = CS
4. If the clutch stack height is less than the basket depth then the diaphragm should be concave (dished in) and this results in more clamping force (compared to flat) and slightly more pull (compared to flat). BD > CS
5. If the clutch stack height is greater than the basket depth then the diaphragm should be convex (dished out) and this results in less clamping force (compared to flat) and slightly less pull (compared to flat). This may result in clutch slippage. BD < CS

Did I miss anything?

I suspect there is an actual answer that would give someone a range for the stack height (perhaps it's a ratio to the basket depth) of what would be an acceptable balance between good clamping force and a light pull. How much variance have you actually seen with the basket depth (stock parts)? I think Matt has a good idea and that's why he can sell a kit.

On my 750 I started to the right of the flat (convex) at got some slipping (pull was extremely light). Moving to the left of flat got me the balance of light pull (slightly heavier than before) and no slipping.

I should have experienced an acceptable pull with my 850 when I set up at a flat diaphragm. Unfortunately at no point did I ever get a decent pull (convex, concave or flat). Luckily someone else suggested the actuator mechanism.

SteveC said:

1.08“ was on my 750. I replaced arm and roller and ball bearing.
when I compared with new the roller did t show much loss, but the arm had worn considerably .

Click to expand...

Did you notice any wear at all on the ball bearing?

To clarify you replaced :
Not shown on this plate 04-0031 Clutch Operating Ball, Chrome, 1/2" (12.7mm)
#33 06-0715 Arm, Clutch Release
#36 04-0060 Roller, Clutch Release

I'm wondering if I should also replace this part.
#37 04-0065 Sleeve, Clutch Release

yes change the pivot #37

swooshdave said:

Did you notice any wear at all on the ball bearing?

To clarify you replaced :
Not shown on this plate 04-0031 Clutch Operating Ball, Chrome, 1/2" (12.7mm)
#33 06-0715 Arm, Clutch Release
#36 04-0060 Roller, Clutch Release

I'm wondering if I should also replace this part.
#37 04-0065 Sleeve, Clutch Release

Click to expand...

Yes, I replaced ball bearing, 33,36 and 37.
No signs of wear on the bearing, hard to tell on the sleeve, just thought it best to replace all the moving surfaces while I was at it.
on mine, the actuator had worn to almost fit the roller. The new one from AN had a larger diameter than the roller. In other words, the roller was sitting on a crescent. Like I said earlier wish I had taken pics.
I wonder how many different basket depths there are? Surely not different for the same year/ Mark?

SteveC said:

Yes, I replaced ball bearing, 33,36 and 37.
No signs of wear on the bearing, hard to tell on the sleeve, just thought it best to replace all the moving surfaces while I was at it.
on mine, the actuator had worn to almost fit the roller. The new one from AN had a larger diameter than the roller. In other words, the roller was sitting on a crescent. Like I said earlier wish I had taken pics.
I wonder how many different basket depths there are? Surely not different for the same year/ Mark?

Click to expand...

I never bother to measure drum height of the "dowel" positioned backing plate and "riveted" held backing plate.
I also do not know if those clutch drum change coincided with thick clutch pack and thin clutch pack.
And of course there are two thick friction plates, solid fiber and bonded segment.

freebe: surflex is a COMPANY they make more than one type of commando clutch plate

swooshdave said:

1. Measure the basket depth (BD) (from backing plate, the one riveted in) to the top of the splines.

Click to expand...

No, not the top of the splines as that's lower than thrust ring.

swooshdave said:

2. Measure the clutch stack height (CS). This is from the bottom plate to the top of the pressure plate (I believe you called it the thrust ring).

Click to expand...

Yes. If you measure it DD's way (and not the OldBritts way).

swooshdave said:

3. If they are the same then you should have a flat diaphragm. BD = CS

Click to expand...

No, BD can't equal CS when measured to the thrust ring of the pressure plate.



However, it really doesn't need to be this difficult.

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. :|"

Nonetheless-
For this torquey 850-
New Barnett friction plates, old steel plates, Diaphragm about flat works very well, even if the owner doesn't quite understand why

1 finger operation, no slip, neutral easy, nice progressive engagement. Venhills cable.
I expect that as it wears it will get a bit more difficult to disengage. It could become a two finger clutch at some future date!



Glen

swooshdave said:

1. Measure the basket depth (BD) (from backing plate, the one riveted in) to the top of the splines.

Click to expand...

L.A.B. said:

No, not the top of the splines as that's lower than thrust ring.

Click to expand...

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. The diaphragm edge does not move up or down from that position.

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!
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, again still referenced from the bottom