Questions concerning Barnett clutch pack.

1403 Views 4 Replies 0 Participants Last post by Guest, Mar 4, 2005

Discussion Starter · Mar 4, 2005

I just installed a Barnett clutch pack into a friends bike last night. Its a 996 and has the corse or DP clutch in it, where the springs are hidden in cups. Anyways.....
Does anyone know if the Barnett springs are a different spring rate than the ones I removed? The reason I ask is they are a smaller I.D., and therefor his DP silver buttons would not fit inside the springs. I used the Barnett springs and caps as I figured its probably a good idea to replace the possibly fatigued springs. The Barnett buttons look cheap though.
What is the significance of the "Curved" plate? The old pack did not appear to have a curved plate. I installed it in the just under center position that Barnett recommended.
What is the difference between putting the "double" pressure plates at the rear or front of the stack? The DP setup had them in the front, Barnett recommended in the rear. I stuck with the DP configuration. I have a feeling this has something to do with at what point in the lever stroke the clutch grabs.
Thanks for your help!

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Discussion Starter · #2 · Mar 4, 2005

Re: Questions concerning Barnett clutch pack. (CuStOm)

I put the Barnett pack in my 748. Here's what I understand:

I would call the curved plate more of a wave than a curve (I pictured a bellville type washer curve, but it's more like a wave spring).

I understand the purpose of this curved plate is to help unload the pack when you pull in the clutch (ie help the plates to separate).

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Discussion Starter · #3 · Mar 4, 2005

Re: Questions concerning Barnett clutch pack. (JamesP)

I think my old eyes are getting tired. If they didn't put the "curved" plate in a bag and mark it, I'm not sure I would even notice the difference. I put the thing where they said, but just because I figure they know something about it. It seems to me the position has changed over the years.

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Discussion Starter · #4 · Mar 4, 2005

Re: Questions concerning Barnett clutch pack. (CuStOm)

Curved/Dished Plate

The key to smooth engagement is controlling the frictional force developed between the smooth plates (that are driven by the engine clutch hub) and the plates that contain friction material (that drive the rear wheel through the clutch basket.)

The amount of force developed between these plates is controlled by the stiffness of the clutch springs, specifically by the amount of preload on these springs. When the clutch is fully engaged, the friction force developed between the plates needs to be greater than the engine’s applied torque to prevent slip. About 430 lbs is needed on a stock superbike.

When you pull-in the clutch lever, the hydraulic pressure applied to the slave cylinder overcomes the spring’s preload and progressively reduces the force pushing the plates together until they begin to slip. During this time the dished plate(s) in the stack act to provide a progressive reduction in the inter-plate force as the plates separate a few millimeters and you get full disengagement.

When you engage the clutch the opposite occurs. The reduced hydraulic pressure on the slave cylinder allows the push-rod to move the spring-loaded pressure plate toward the plate stack (a millimeter or so) until the plates begin to touch. Keep in mind that when you move the lever you are changing the POSITION of the pressure plate. You have only indirect control over the forces between plates.

The forces between plates is controlled during this transition (between disengaged and fully engaged) by a dished plate that is included in the stack to smooth this transition. This plate acts as a spring (pushes back with a force) when it gets flattened between adjacent plates by the movement of the pressure plate.

So, the force pushing the plates together first come from the smaller force produced by flattening the dished spring plate, and later, a much greater force produced by the preloaded clutch springs.

The higher the height of the clutch pack, the greater the clutch spring preload. So, as the clutch pack friction material wears-out, the pack height gets shorter, until the force between plates is insufficient and the clutch slips, at first under high torque conditions such as at launch, and later even when the lever is not pulled at speed. Time for a new clutch.

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Discussion Starter · #5 · Mar 4, 2005

Re: Questions concerning Barnett clutch pack. (Shazaam!)

Thanks Shazaam!
So looking at one of my other questions, are the springs the same rate in the Barnett pack? With the addition of the "curved" plate, I would think that the springs would need to be a slightly higher rate to overcome the spring in the curved plate.
Also, Whys do the outside plates wear at a much quicker rate than the inside plates? Should the pressure not be evenly distributed?

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