Clutch Stack Revisted

DogT · Apr 22, 2015

So it looks like the thing to do without a lathe is select parts for the correct diaphragm shape, to hell with the clutch pack height? Maybe this explains why some have easy clutches and some not.

pete.v · Apr 22, 2015

DogT said:
So it looks like the thing to do without a lathe is select parts for the correct diaphragm shape, to hell with the clutch pack height? Maybe this explains why some have easy clutches and some not.

Yes, I think it is relative to some extent. I think that is why Old Britts sell the drive plates with different thickness. You buy the set, use the one that works and send the others back for credit. (for those without a lathe)

http://www.oldbritts.com/ob_clutch_info.html

Nater_Potater · Apr 22, 2015

pete.v said:
I think that is why Old Britts sell the drive plates with different thickness. You buy the set, use the one that works and send the others back for credit. (for those without a lathe)
http://www.oldbritts.com/ob_clutch_info.html

Cheap, and no lathe access, I took a bit different approach back in the fall of '14. clutch-actuating-mechanism-thoughts-t20404.html about a third of the way down the page.
So far, it still works a treat.

Nathan

DogT · Apr 22, 2015

I tried the OB clutch set and there was none thin enough to work on my clutch without slipping. I probably need something in the .030-.040 range. I measured the Barnet plain plate I got and it's .075 or so. So my only other option is Jim's method most likely.

Brooking 850 · Apr 22, 2015

I had to machine my pressure plate in the race bike by approx 0. 050" to get this right recently from .230" to .180' ( i think these figures are correct) as my diaphragm sat a little less concave than ideal and the clutch would slip off the line briefly which gave poor starts and also at around 6200 to 6500 rpm under load, which was a pain as I always had to feather the throttle to get it to grip.
It is a 4 x 5 plate combination using bronze plates in Maney basket. Now seems solid
Regards Mike

Deets55 · Apr 22, 2015

DogT said:
I tried the OB clutch set and there was none thin enough to work on my clutch without slipping. I probably need something in the .030-.040 range. I measured the Barnet plain plate I got and it's .075 or so. So my only other option is Jim's method most likely.

DogT,

Barnett friction plates for the 750 are thicker that the 850. You might be able to mix and match the different friction plates to come up with the number you need. From memory I think it is .145" (750) and .121" (850). This way you can deal in increments of .024"

Pete

worntorn · Apr 22, 2015

Will the 850 clutch stack with it's extra plate but thinner plates fit into the 750?
Seems a good plan to add the friction area if possible, then pressure can possibly be kept a bit lower and still hold?

Glen

Deets55 · Apr 22, 2015

Glen,

I am pretty sure the plates are exactly the same except for the thickness. The thinner plates are for the 5 friction plate system while the thicker plates go in the 4 friction plate system. Check out the Barnett site. When I put mine together last time I checked my shop manual. It showed friction plate and steel plate thickness. I just added them up and put together a stack that matched the total. You just have to make sure you have the correct pressure plate that goes with your bike to get the right height. The spring is concave at rest and I believe almost flat with the lever pulled in. That can change depending on how you adjust the clutch and what ramp you have. I did this the beginning of last summer and it is still perfect. If I had used all new fiber plates the only thing I would change is make the stack slightly higher at the beginning to allow for break in with new fiber plates.

Pete

L.A.B. · Apr 22, 2015

worntorn said:
Will the 850 clutch stack with it's extra plate but thinner plates fit into the 750?

The so-called '850' 5-plate clutch was originally introduced on the late 750 models (from 212278).
The clutch drum is the same for both 4 and 5-plate clutches but the 5-plate pressure plate is thinner.

http://atlanticgreen.com/clutchpak.htm

pete.v · Apr 22, 2015

Deets55 said:
. The spring is concave at rest and I believe almost flat with the lever pulled in.

Pete

Mine is convex at rest (although you could argue that it is flat) and more convex with the lever pulled in.

This action was being performed with one finger, of course. In all the time/years I have had this set like this, the clutch has never ever slipped. This is a 5 plate 850 setup on my 750. I recommend this to anyone.
[video]https://www.youtube.com/watch?v=c8RjSvg-aME[/video]

Deets55 · Apr 22, 2015

L.A.B. said:
worntorn said:

Will the 850 clutch stack with it's extra plate but thinner plates fit into the 750?

Click to expand...

The clutch drum is the same for both 4 and 5-plate clutches but the 5-plate pressure plate is thinner.

That might explain why pete.v has a convex spring at rest?

CanukNortonNut · Apr 22, 2015

L.A.B. said:
worntorn said:

Will the 850 clutch stack with it's extra plate but thinner plates fit into the 750?

Click to expand...

The so-called '850' 5-plate clutch was originally introduced on the late 750 models (from 212278).
The clutch drum is the same for both 4 and 5-plate clutches but the 5-plate pressure plate is thinner.

http://atlanticgreen.com/clutchpak.htm

I agree. Good mod upgrade, if you are using an older thicker type pressure plate. You can machine the older plate down to the thickness of the later style then add another 1-steel/1- friction plates to the mix.
But I would do as Jim C does and machine thickness to suit the stack height to get the sweet spot.
Cheers,
Thomas
CNN

swooshdave · Apr 23, 2015

DogT said:
I tried the OB clutch set and there was none thin enough to work on my clutch without slipping. I probably need something in the .030-.040 range. I measured the Barnet plain plate I got and it's .075 or so. So my only other option is Jim's method most likely.

I'm surprised you couldn't find a combination that would work.

comnoz · Apr 24, 2015

pete.v said:
Deets55 said:

. The spring is concave at rest and I believe almost flat with the lever pulled in.

Pete

Click to expand...

Mine is convex at rest (although you could argue that it is flat) and more convex with the lever pulled in.

This action was being performed with one finger, of course. In all the time/years I have had this set like this, the clutch has never ever slipped. This is a 5 plate 850 setup on my 750. I recommend this to anyone.
[video]https://www.youtube.com/watch?v=c8RjSvg-aME[/video]

With that rgm clutch drum you can't run a concave spring without doing some machine work. You could take the clutch plats out and install the spring and when you released the holding tool the diaphragm can only go flat. The space for the spring is not wide enough to allow it to go concave. I always machine the outside splines down just enough to let the diaphragm go a little concave. Jim

but hey -if it works, it works

swooshdave · Apr 24, 2015

My RGM clutch with Barnett discs works great. No more needed.

Fast Eddie · Apr 24, 2015

Ludwig, please do tell us what you have done, the uninitiated (like me) have difficulty with the concept of throwing away 'half of what's inside' as we kinda think "but that IS the clutch"!

I'm sure that you will have looked into the whole assembly with a far more careful eye than most... So please... Do tell...

DogT · Apr 24, 2015

swooshdave said:
DogT said:

I tried the OB clutch set and there was none thin enough to work on my clutch without slipping. I probably need something in the .030-.040 range. I measured the Barnet plain plate I got and it's .075 or so. So my only other option is Jim's method most likely.

Click to expand...

I'm surprised you couldn't find a combination that would work.

Like I say, the thinnest was too much. I may try like Deet suggests and get a thinner friction plate, then maybe I can slip that .075 plate in there. That would give me some more, but not .075. I'll have to study that diaphragm action too.

I see dynodave dropped out, I hope he didn't think we were ignoring him. His info is good, it's just very confusing for us backyard mechanics.

Yeah, I'd like to see ludwig's ideas too. Everything he does I like, but I have to say I haven't incorporated any of it. If I made another bike.....

pete.v · Apr 24, 2015

ludwig said:
I am happy for you that your clutch works fine , but it is way too big .
It sticks out of the belt like a sore thumb .
Cut that drum down to 32 mm and throw out half of the stuff that is inside .

Thank you for the awesome tip, Ludwig. I will get right on that.

FWIW, I have done much testing and adjusting to get the belt to ride consitantly to the inboard side of the hubs with no interference or rubbing. I find this to be most desirable to the contrary.

swooshdave · Apr 24, 2015

ludwig said:
Pete .v ,
If you ever have the chance , install your complete clutch on a mainshaft , put it in a lathe and spin it to 3000 rpm .
You will likely get an idea of the forces involved .
A standard 850 clutch , with the extra steel plate like often recommended , weights 6 kg .
With a little effort , you can bring that down to 2.5 kg or less .
That makes a huge difference in rotational energy .
All you need is 3 narrow steel an 4 fibre plates , an alloy back plate and a thin alloy pressure plate .
It will all fit in a 30 mm wide basket .
Instead of adding stuff to get to the correct stack height , why not removing it ?

Because not everyone has access to a lathe? Sound incredible but it's actually true. So for us mere mortals we have to play with stack height and not the clutch size. :mrgreen:

BritTwit · Apr 24, 2015

swooshdave said:
Because not everyone has access to a lathe? Sound incredible but it's actually true. So for us mere mortals we have to play with stack height and not the clutch size. :mrgreen:

Wow!

Sounds great, but I too am lathe-challanged.
Is there any place like maybe CNW that can perform this service for interested owners?

Clutch Stack Revisted

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