CNW Easy Pull Clutch Kit?

L.A.B. have you adjusted your stack height on your MK3? If so, what size plate did you use?
 
L.A.B. said:
The diaphragm actually works the opposite way. Increasing the stack height reduces clamping pressure and vice versa and why the action now feels lighter.

It's possible the clutch will be ok with the 3mm increase in stack height if it was as low* as you measured but only a road test will answer
that.
*The accuracy of the measurement depends on how precisely the spring is adjusted to 'flat' using the spring compressor because any (concave or convex) 'dish' remaining in the spring between the pressure plate ring and the periphery of the spring will result in an inaccurate stack height measurement.
Click to expand...

I'd thought that the maximum pressure was when the plate is flat, so when the stack height is too low, the clutch lever has to move from, say, concave with 80% pressure, through 100%, to the 80% convex, so the whole lever action was going through the toughest part of the pressure range.

With the stack height adjusted so that the diaphragm is flat, I'd thought that the lever would move from 100%, through convex at 80%, on to 60%, and that is why it felt so much better. The actual % numbers are a complete guess, but just to illustrate the thinking. Is this not correct?
 
MichaelD said:
I'd thought that the maximum pressure was when the plate is flat, so when the stack height is too low, the clutch lever has to move from, say, concave with 80% pressure, through 100%, to the 80% convex, so the whole lever action was going through the toughest part of the pressure range.
Click to expand...

It's the opposite, as the spring approaches 'flat' the spring pressure is reduced resulting in less clamping force and less effort is then required to lift the spring.

Increasing the stack height moves the range between the "Clutch Fully Home" - "Clutch at Full Lift" lines further away from the spring's point of maximum clamping force (the peak to the left of the clutch range) on the diagram, below:
CNW Easy Pull Clutch Kit?
 
Many of us have belt drives with different clutch baskets or worn or different brands of clutch plates etc etc. What we need is an ideal measurement of the diaphram at rest - is it flat or concave and how much? And we need the ideal measurement of the diaphram with the clutch lever pulled - is it flat or convex and how much?

I remember changing the diaphram height on my small block ford and it make a huge difference. I'm going to make a statement that I hope is true - you want your Commando diaphram to be convex with the lever pulled and flat with the lever released. Somebody please verify or correct this. I'm going to makes some experiments later today.
 
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jseng1 said:
Many of us have belt drives with different clutch baskets or worn or different brands of clutch plates etc etc. What we need is an ideal measurement of the diaphram at rest - is it flat or concave and how much? And we need the ideal measurement of the diaphram with the clutch lever pulled - is it flat or convex and how much?
Click to expand...

The problem is the variation in the number of friction plates, their friction coefficient, spring strength (old/new?) and whether the clutch is run completely dry (as with many belt drives) or has to cope with primary oil splash for there to be a single ideal measurement in my opinion, as a totally dry clutch, for instance, would require less clamping force so could be run with a higher stack height (so flatter spring) than one having 'wet' plates.
 
jseng1 said:
I'm going to make a statement that I hope is true - you want your Commando diaphram to be convex with the lever pulled and flat with the lever released. Somebody please verify or correct this. I'm going to makes some experiments later today.
Click to expand...

With the stack height adjusted then the clutch spring should already be close to flat so will pass through flat as the clutch is operated and the force required to pull the clutch lever should reduce as the lever moves closer to the bar grip (the spring passing through flat) see the previous diagram that shows the diaphragm spring force reduces between "Fully Home" and Full Lift".
 
With my original setup the diapham was concave with the lever out and nearly flat with the lever pulled. I was just able to fit in an extra steel plate next to the cast iron plate and now the pressure is greatly reduced at the lever. Now the plate is barely convex with the lever out and more convex with the lever pulled. Took it for a test ride and no slippage so far (dry belt drive).
 
jseng1 said:
With my original setup the diapham was concave with the lever out and nearly flat with the lever pulled.
Click to expand...

The stack height must have been fairly low to begin with if the spring didn't go convex with the lever pulled in, that's assuming the clutch actuator is the standard Commando one and not the lower lift Dominator/Atlas type or shorter clutch lever pivot radius, etc.
 
L.A.B. said:
The stack height must have been fairly low to begin with if the spring didn't go convex with the lever pulled in, that's assuming the clutch actuator is the standard Commando one and not the lower lift Dominator/Atlas type or shorter clutch lever pivot radius, etc.
Click to expand...
I use the Atlas clutch lever pivot to reduce lever tension.
 
L.A.B. said:
It's the opposite, as the spring approaches 'flat' the spring pressure is reduced resulting in less clamping force and less effort is then required to lift the spring.

Increasing the stack height moves the range between the "Clutch Fully Home" - "Clutch at Full Lift" lines further away from the spring's point of maximum clamping force (the peak to the left of the clutch range) on the diagram, below:
Click to expand...

Thanks, I'd seen this diagram before, but it didn't show where the diaphragm spring is concave, flat, and convex, so I couldn't get much useful information from it. Is the first peak of pressure when the plate is flat, which was my understanding? Or is the point where the diaphragm is flat at the bottom of the dip?
 
MichaelD said:
Is the first peak of pressure when the plate is flat, which was my understanding?
Click to expand...

No, the spring would still be some distance from flat at the peak and not within the operating range of the clutch which begins at the "Clutch Fully Home" position and is past the peak.

MichaelD said:
Or is the point where the diaphragm is flat at the bottom of the dip?
Click to expand...

Flat should be on the straight downward section between the end of the peak curve and the beginning of the dip curve.
 
Did the deed fitting a thicker steel plate, the RGM 4mm, replacing one original plate. This moved the diaphragm from slightly concave to noticeably convex. Lever load went from 21-24 lbs to about 12-14. I also tried a 3mm RGM plate instead, gave slight convex and about 16-17 lbs at lever. Test riding with 4mm all seems good, no detectable slipping.
 
L.A.B. said:
If true then there'd be no need for "easy pull" clutch kits and clutch pull can often be improved by 'tuning' (usually increasing) the stack height.



Unworn clutches can also benefit from the increased stack height as it is often 'low' even with new plates.

My Mk3's clutch pull was certainly lighter after fitting RGM's 3mm plain plate and that was shortly after fitting new (Surflex) friction plates.
Click to expand...

As I have said before I am still running my original clutch plates that came from the factory and after 46+ years the only thing I have replaced in my stock clutch is the pressure plate and clutch centre and that's was just over 12 years ago, my clutch plates have 160k miles on them, I have never done stack height and can easily pull my clutch with one finger if I want to so a full hand it feels so light, I have used the bronze/steel plates when running a belt drive and dry primary, but when I did the clutch did bite a bit quicker but got use to that, I ran the belt for about 5 years before going back to chain.
My 850 has always had a light clutch from new so I really can't understand why so many have troubles with a heavy clutch but of course every bike is different.
I did use fibre plates once when I went belt drive and I had misplaced my orginial plates for about 1 year then I found where I had my original plates in a container of oil and a old primary chain sitting on top of them, I replaced the fibre plates when one split in half and showing wear, all I did to the original plates was give them a good clean and a light sand paper rub.
Since using ATF - F I have never had a sticking clutch and it's been so long since I have had the clutch plates out, well 12 + years ago when I replaced the clutch centre and pressure plate, it lost its spring and was flat.
I have never had GB oil in my primary just put grease on the clutch rod, very rarely adjust my clutch usually when the lock nut comes lose and I run a venell cable with a straight run and orginial levers.
I went back to chain primary after wearing a few belts, not the teeth but side wear and the belt trying to run off even with 2 adjusters and the pully guide shatted from the force this happened after 3 years running the belt without any problems, then the next 2 years it just kept wearing the sides of the belt.
To be honest running belt or chain I find no difference in running smooth between the both only the belt drive is lighter and maybe a little higher gearing but other than that nothing, but the chain has a bit more give and not needed to be perfect in the adjustments run, next time I replace the chain I will go with the chainman duplex chain.
I have been running a sealed clutch bearing for about 40 years and every so often will service/inspect the clutch and pull the bearing seals out give the bearing a good clean and inspection and repack if still good but they are cheap if it needs replacing.
Been just over 12 years since I done a pull down and inspection about 35k miles ago so next maintenance service will get a good pull down and clean.

Ashley
 
Update:
First ride out on highway since fitting one 4mm plate in place of one standard plate. All seemed fine until some twenty minutes in to the run, at some 60mph in fourth, rapidly twisted up to be 3/4 full throttle and had some clutch slip. Was repeatable a few times. So i'll be dialing it back a bit. I have a 3mm plate as well. Just exchange it for the 4mm or doing something more clever? Suggestions?
 
Tornado said:
I have a 3mm plate as well. Just exchange it for the 4mm or doing something more clever? Suggestions?
Click to expand...

You might find the 3mm plate alone is light enough, or, you could fit the 3mm plate and replace one 'thin' (5-plate) friction plate with a 'thick' (4-plate) friction plate as that would reduce the stack height from +4mm +2mm to approximately +3.5mm +1.5mm but I'd suggest you try just the 3mm plate first.
 
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