Clutch, dry - Stack Height questions - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 14 (permalink) Old Apr 20th, 2017, 1:15 am Thread Starter
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Clutch, dry - Stack Height questions

2008 Hypermotard 1100.

The Ducati manual states (if it is to believed; also states I have a wet clutch) that the stack height should not be less than 46.1 mm, how do I find/figure out what the maximum height is?

I replaced the clutch pack (aftermarket, Ducabike) last month and it was performing great. I've started to feel some slippage here and there, not consistent, just a bit. I pulled the plates for a quick inspection and there's still plenty of material, in-fact they still look new. I suspect it's bedded in a bit and has just dropped the stack-height under the minimum and the pressure plate is just about sitting on the drum. I'll measure it again this weekend just to make sure.

So what I'm wondering, aside from the springs possibly being weak (coincidentally I have a blingy set on order), I should add another plate or mix & match the driven plates to bring the stack up to the correct height.

What is the correct stack height or what is the limit for the pressure plate to stay engaged on the clutch drum?

2008 Hypermotard 1100
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post #2 of 14 (permalink) Old Apr 20th, 2017, 3:38 am
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Measure the stack height of what you have. Let us know. I doubt you would have gone from new to minimum in such a short time. To many plates and you risk one falling between the pack and the pressure plate. You should be able to work this out on your own by looking at the pressure plate when you disengage (pull the lever in) the clutch.
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post #3 of 14 (permalink) Old Apr 20th, 2017, 8:27 am
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Too many plates or too high a stack and you won't have enough travel in the slave to release the clutch.

'96 Ducati SS900CR, '07 S4RS, '06 Busa, '77 Bonny,
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post #4 of 14 (permalink) Old Apr 20th, 2017, 11:18 am
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Make sure that the oil that you're using is suitable for a wet clutch or you'll get slippage.
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post #5 of 14 (permalink) Old Apr 21st, 2017, 3:20 am Thread Starter
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What kind of oil does one use on a dry clutch? Just kidding...
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post #6 of 14 (permalink) Old Apr 21st, 2017, 3:28 am Thread Starter
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Hmmm... noob time.... the stack height is 40.6 and the springs are all under 40. One could say therein lies the problem. I'm going to readjust with the stock driven plates and see where that brings me. Springs I'll take care of later.
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post #7 of 14 (permalink) Old Apr 21st, 2017, 3:51 am
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Quote:
Originally Posted by Sideburn View Post
Hmmm... noob time.... the stack height is 40.6 and the springs are all under 40. One could say therein lies the problem. I'm going to readjust with the stock driven plates and see where that brings me. Springs I'll take care of later.
The plates and hence stack height are on the "inside" of the pressure plate.

The springs are on the "outside" of the pressure plate and hence unrelated to stack height.

Measuring the spring length is just a way to check if their "springiness" is OK.
They are the things that push the pressure plate to make sure there is correct pressure to hold the stacked plates sufficiently tightly together.

If the stack height is too low, then the pressure plate cannot apply the correct pressure as it is limited on how far onto the hub it can go.

When you installed the pressure plate, did you put it in the correct rotational position?
On my 900SS there is a mark on the pressure plate that has to be aligned correctly with a position on the hub.
Only from memory, one of the "pillars" on the inside of my pressure plate has a slot in it which would limit how far onto the hub it can go if not in the correct position.

Richard Collins - 2001 900SSie
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post #8 of 14 (permalink) Old Apr 21st, 2017, 5:46 am
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i don't think i've ever seen springs that need to be replaced. i pulled some s4rs springs out today and they were 38.2mm.

the 40.6 sounds about right. i modified the s4rs pack today, replacing all the 2mm steels with 1.5mm and added another friction plate to mimic the 1098, 1100, etc pack and and that was 39mm. out of the box that pack is 41mm or so? original 7 friction pack is 38.5 new from memory.

the thicker the pack the more preload on the springs. the pack has to be very thin for the pressure plate to hit the drum, unless you have a different pressure plate that's not deep enough - seen that before.

when does it slip?

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post #9 of 14 (permalink) Old Apr 21st, 2017, 5:58 am Thread Starter
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First of all, the spec in the factory manual is BS. If I put the factory stack height on the drum, there's no room for the press.plate to sit. I have it adjusted now to where the press.plate still stays on the drum when dissegaged and applies full available pressure to the clutch. It is a stock drum btw. I also found out I need to replace those tiny shaft o-rings but that's another issue. I' ll get some next week.
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post #10 of 14 (permalink) Old Apr 21st, 2017, 6:02 am Thread Starter
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Sometimes it slips under load, hot or cold engine no difference. I can get the front end to come up in first or second on its own without assistance and didn't notice the slippage. Wonder if it's the master or slave acting up a bit...
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