Adjusting the Slipper Clutch
(12 July 2006)

posted by neil (6/23/05 1:44 am)

My new Tre has a diabolical clutch - very intrusive awkward action. Many thanks to Johnny O for his input to the "RS slipper clutch" thread explaining why..
Leading from which...
Given the poor availability of Benelli parts, Johnny mentioned that some of the fibre plates may have been Honda CR250 'KA4'. Anybody know if the steel plates interchangable with the CR250 (or something else) too?
Johnny O - probably asking you I guess, I wonder if you get any time to earn a living as well as look after us?

Johnny O (6/23/05 2:36 am)

Hey Neil, sorry I haven't compared the Tornado steel clutch plates with anything else, and I was only guessing with the CR250 fibre's. You shouldn't need to change them anyways.
What is the problem with your clutch?

neil (6/23/05 4:19 am)

Thanks again Johnny-
Clutch lever travel is huge (10mm plus at the lever end) in response to deceleration/acceleration - you suggest this is due to clutch stack being too short in your other thread. How can this be overcome other than selective assembly of clutch? Thought that using a ground to size steel plate would allow easy adjustment.(Surface grinder available!)
(I'm only familiar with the Aprilia slipper, which is totally different, and am (I think!) competent enough to figure it out once I take the cover off, just trying to shortcut the process before getting the spanners out!)

Johnny O (6/23/05 4:45 am)

Okay Neil, here we go.... I guess most of this won't make sense to you until to get into it.
Once you have removed the pressure plate, you will see the steel plate in the center of the clutch boss that slides along a spiral center boss and lifts the pressure plate off the clutch plate stack. Now you can either increase the clutch plate stack (probably about 1.00mm) or you can get the base of the six towers that the main clutch springs sit in, machined the same amount.
You see, when you shut the throttle off, the steel plate in the center of the clutch rotates on the spiral boss and pushes against the bottom of the six spring towers of the pressure plate causing the clutch to slip on decelleration (did I spell that right?).
I think rather than stuff around with finding different thickness clutch plates, machining the base of the six clutch spring towers might be easier if you know someone that can grind/machine it.
You can generally reuse the clutch cover gasket so you shouldn't need any parts to do this mod.
While you've got the clutch apart, if you can let me know the height of all six clutch springs, I can then suggest what springs will offer the lightest lever pull without slipping when 'on the gas'.
Machining the pressure plate as I have explained will not affect the lever (at the handlebar) resistance or the spring pressure on the clutch stack; if you made up a 1.00 mm higher clutch stack, this would increase the clutch spring pressure and you would feel it at the lever.

neil (6/23/05 7:47 am)

Thanks for guidance Johnny -
Damn - you made me check the dictionary! "Decelerate" and "Accelerate" are correct according to the Oxford dictionary! Maybe different in the USA, but Australian spelling is normally closer to UK English in my experience?
Full machining facilities at work (University Engineering dept) so machining the pressure plate sounds favourite. (Used to heavy, dragging clutches, got a 1976 Jota too.) Again, many thanks for your help and guidance. Presumably if I machine too much off, the slipper just never reaches the pressure plate and stops working? (Which I could easily live with)

neil (6/23/05 9:13 am)

All makes sense now - looks like I have about 2.2mm of pressure plate lift when the slipper plate is hard up against the round washer that stops it.
I'll recheck the measurements before cutting metal, but what's the IDEAL lift at the pressure plate for fast road riding? You mentioned 0.9mm? (I am ex-Isle of Man and short circuit racer, ageing now but not forgotten how:) )
Clutch springs are 3 at 33mm and 3 at 37mm measured with a crap vernier so only approx!

Johnny O (6/23/05 5:14 pm)

Neil, I think you have the perfect spring combination for the street, I run 6 of the longer ones on the track, as you would know, the bike spends a lot more time at full throttle and you don't want it slipping after you've fried it off the line.
On my bike (my first 903 model) I machined 1.80mm off the base of the pressure plate so I had .8mm of lift but I think anywhere between .5mm and 1.00mm lift would be okay to live with. I guess I'm like you, I do not need a slipper clutch (just give it a good blip on downshifts), I was thinking of putting the TNT center boss in the Tornado, from looking at the parts list diagram, it looks like it does not have a slipper.
I rode at the TT in 1990, I hadn't been racing very long then and was coming back from a brain injury (so that explains it ;) )suffered in a big crash, I just floundered around like a real wally (as the jacket denoted). Riding in the F1 class, aboard a GSXR750, was not a good idea for my very first time there either ;) I was just going there to watch but as I am a Pro rider here, they offered me 850 pound to ride; so I thought, 'why not?' BLOODY AWESOME is all I can say about it :D

neil (6/24/05 2:56 am)

Just taken 0.9mm off the pressure plate - It's so easy to get to, I thought I'd experiment and take material off in a number of "goes" until I've gone too far! Off road riding weekend, I'll report back early next week on how it feels. Glad you enjoyed (!) the Isle of Man - but they only gave me £250 start money for the '89 Proddy race :( Went back to the Manx Grand Prix after that, couldn't compete against professional teams on my salary! colin (6/26/05 12:07 pm)
johnny o, could you tell me if the tnt has the same prob w.r.t the neutral prob.if they don`t can they be fitted to 903 tre.
had clutch apart and you`re right they are pretty simple.
measured clutch spring length with vernier 34 mm all of them.the amount of pressure you need to operate clutch is even more than my old 748 duke.
i was thinking of using some lower tension compression springs 1. to stop clutch dragging and 2. for a lighter action at lever.
obviously i`m gonna have to play with tension so i get no slip .what do you think (obviously i`ll have to play about with slipper clutch as i guess it will try to operate sooner)

Johnny O (6/26/05 7:15 pm)

The TNT doesn't have a slipper clutch but that is not the reason it is easier to to get neutral. You already have the shortest Benelli clutch springs fitted, you must have a late model? Changing the clutch spring will not affect the neutral selection problem; if you have the newer, shorter, steel clutch actuating arm fitted and all but 1.00mm of freeplay is adjusted out of the clutch cable, you could see if you have any warped clutch plates (steel ones) that could be causing the clutch drag, as that is the only thing preventing neutral selection, I think.