Request for advice reference slipping clutch

If you need technical information or help with your late dry clutch Ducati S2, MHR 900 or Mille engine - post your FAQs, comments & questions here.
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Blacklightning
Diana
Posts: 62
Joined: Tue Oct 18, 2011 12:35 pm
Location: Gerrards Cross

Request for advice reference slipping clutch

Post by Blacklightning » Sun Jul 21, 2013 11:56 am

Evening All,

Ducati 900 Replica 1979 number 146 - running in almost completed at 2000 miles now and upping the revs for short bursts to 6k.

The bike has completed 1500 od miles at 4.5k revs maximum superbly,as I am now increasing the revs slightly I am occasionaly finding that under hard acceleration the clucth will slip slightly until it grips.

If I feed in the revs gently then its fine.

Clutch lever has free play, clutch is (I think) engaging fully and as I say, all has been fine on lower revs.

I have read road tests from the 1970's and 80's saying this was an issue.

Anything particular to have a look at or do to try and solve the problem - or is it something to live with?

Regards

Stuart

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Craig in France
Cagiva Elefant
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Re: Request for advice reference slipping clutch

Post by Craig in France » Mon Jul 22, 2013 7:12 am

2 things, Stuart.

1. Change the springs for 450 springs. This was the fix at the time, btw. However, to avoid ending up with too strong a pull, try first with 3x 450 springs and 3x what you've got now.*

* And stop dumping the clutch .. :-D (Nah, only pulling yer pi**er...).

P.s Check your existing spring lengths, too: minimum 28.9mm.

2. What oil are you running? if you've changed to a synthetic where previously it was running a mineral, this can cause clutch slip.

Easy fix. Remove the plates, wash them in parafin, leave to dry, light re-oil and refit. And while they're out:
1. Visually check the wear on the driving plates.
2. Check the thickness of the total clutch pack. It shouldn't be below 37.5mm. If it is, fit a new clutch pack.*
3. Visually check the driven plates for flatness and remove any accumulation of crud (use fine emery or wet & dry)

* Depending on your budget vs. how much you value your time :-D , you might decide to go down this route anyway ...

P.s Don't forget: the final driven plate is a special: bent tabs face Inwards. As is the first driving plate, according to the parts book. But I can't now remember in what way or why ...

P.p.s Don't forget to get a new clutch cover gasket. 'Cos if you don't have one ready and waiting, you can guarantee that the old one is gonna leak ...

HTH

Craig

Blacklightning
Diana
Posts: 62
Joined: Tue Oct 18, 2011 12:35 pm
Location: Gerrards Cross

Re: Request for advice reference slipping clutch

Post by Blacklightning » Tue Jul 23, 2013 3:15 am

Hi Craig,

Great advice as ever, thanks.

Having been running in on Chatsworth Silkolene Straight 40 changed at c250 mile intervals.

I was going to go synthetic but a few folks mentioned clutch slip so I think I may stick with what I have been using.

As the clutch slip is occasional and can be avoided by feeding in power I am tempted to leave it for the Manx - though buy the clucth pack and springs and take them with me - if it develops worse then I have the tools and parts, if not - then I will leave well alone till after the Manx.

Cheers for now.

Stuart

bobnorton
860 GT / GTS
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Location: bromley kent

Re: Request for advice reference slipping clutch

Post by bobnorton » Tue Sep 10, 2013 11:19 am

In theory the clutch springs should all be of equal strength so the clutch should lift and grip evenly. Mine did not. had to pack out 2 springs to get the clutch to lift and settle back properly.

bobnorton
860 GT / GTS
Posts: 282
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Re: Request for advice reference slipping clutch

Post by bobnorton » Tue Sep 10, 2013 11:22 am

In theory the clutch springs should all be of equal strength so the clutch should lift and grip evenly. Mine did not. had to pack out 2 springs to get the clutch to lift and settle back properly.Also the pushrod can seize and not allow the clutch to settle back .

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abmartin
SSD900 Darmah
Posts: 357
Joined: Tue Apr 10, 2007 4:08 pm
Location: New Brunswick, Canada

Re: Request for advice reference slipping clutch

Post by abmartin » Thu Sep 12, 2013 3:39 pm

I took a look at my Ducati Tuning book by Stephen Eke. He maintains that the 450SCR clutch springs won't work on left-hand gearshift models because they have revised clutch baskets with longer springs. He says that using elliptically ground steel plates are sufficient to cure any slipping problems. My '79 SS has Surflex plates, I don't know if this was standard at the time, and, knock on wood, I have never had any clutch problems. I use 40 weight diesel oil in the motor.

Bruce

Shouldn't this post be in the squarecase Bosch-equipped motor section? We are dealing with a wet, not dry, clutch motor aren't we?
1979 900SS
Fredericton, NB
Canada

Blacklightning
Diana
Posts: 62
Joined: Tue Oct 18, 2011 12:35 pm
Location: Gerrards Cross

Re: Request for advice reference slipping clutch

Post by Blacklightning » Fri Sep 13, 2013 12:31 am

I'm about to strip number 146 (1979 Ducati 900 Replica) having now successfully completed the Manx Grand Prix Closed Roads Parade Lap on the Isle of Man on Saturday 24th August.

I've bought a Sureflex Kit and intend to fit that.

I did 8 laps on open roads in preparation for the Parade and the bike performed fine, managed to gently power on out of Ramsey Hairpin, the Gooseneck and out of Bungalow up Hailwoods Rise to the highest point on the course. Occasional slight slipping but manageable. :-D :-D

However...then the Parade Lap - bit more enthusiastic tee hee - and rather a bit of slipping....rounded Ramsey Hairpin and took a TZ250 on the inside, poured on the revs to out drag him and went nowhere... :shock:

Then ditto a Matchless G50 at Gooseneck, lovely line through the inside and poured the petrol on the bonfire......nothing. :shock:
So the clutch is going to be changed - can't have that for next year.........

Then Sunday my mate dropped my Ducati.....ouch - but that's another tale......... :cry: :cry:

Keep everyone posted on the outcome of the Sureflex Kit. :-D

Stuart

Blacklightning
Diana
Posts: 62
Joined: Tue Oct 18, 2011 12:35 pm
Location: Gerrards Cross

Re: Request for advice reference slipping clutch

Post by Blacklightning » Fri Sep 13, 2013 12:37 am

abmartin wrote:I took a look at my Ducati Tuning book by Stephen Eke. He maintains that the 450SCR clutch springs won't work on left-hand gearshift models because they have revised clutch baskets with longer springs. He says that using elliptically ground steel plates are sufficient to cure any slipping problems. My '79 SS has Surflex plates, I don't know if this was standard at the time, and, knock on wood, I have never had any clutch problems. I use 40 weight diesel oil in the motor.

Bruce

Shouldn't this post be in the squarecase Bosch-equipped motor section? We are dealing with a wet, not dry, clutch motor aren't we?
I think you may be right - but I just post in the "MHR" section whilst recognisng the clutch is wet....there doesn't appear to be any other reference to the MHR in the Board Index.

Bruce,

Any chance you could post from the Ducati Tuning Book how to set the clutch up (fitting the cable, setting the adjustment, free play at operating arm, not touching cases etc and then cable fitting and handlebar adjustment) - I don't have the book you refer to and have trawled through the workshop manuals and exploded engnie and parts diagram without joy, can't find anything telling me how to set up the clutch?

It's kinda obvious I guess - but I would love specific details from a tuning book with experience showing/instructing how to do it....

Cheers

Stuart

Blacklightning
Diana
Posts: 62
Joined: Tue Oct 18, 2011 12:35 pm
Location: Gerrards Cross

Found it in the wet clutch section...

Post by Blacklightning » Fri Sep 13, 2013 12:45 am

Blacklightning wrote:
abmartin wrote:I took a look at my Ducati Tuning book by Stephen Eke. He maintains that the 450SCR clutch springs won't work on left-hand gearshift models because they have revised clutch baskets with longer springs. He says that using elliptically ground steel plates are sufficient to cure any slipping problems. My '79 SS has Surflex plates, I don't know if this was standard at the time, and, knock on wood, I have never had any clutch problems. I use 40 weight diesel oil in the motor.

Bruce

Shouldn't this post be in the squarecase Bosch-equipped motor section? We are dealing with a wet, not dry, clutch motor aren't we?
I think you may be right - but I just post in the "MHR" section whilst recognisng the clutch is wet....there doesn't appear to be any other reference to the MHR in the Board Index.

Bruce,

Any chance you could post from the Ducati Tuning Book how to set the clutch up (fitting the cable, setting the adjustment, free play at operating arm, not touching cases etc and then cable fitting and handlebar adjustment) - I don't have the book you refer to and have trawled through the workshop manuals and exploded engnie and parts diagram without joy, can't find anything telling me how to set up the clutch?

It's kinda obvious I guess - but I would love specific details from a tuning book with experience showing/instructing how to do it....

Cheers

Stuart
Bruce - Just found a very helpful thread in the wet clutch engine section with loads of diagrams, mesurements, discussions on parts, recommendations on cleaning and lubrication and, finally, instructions on assembly and adjustment - so I think I may have what I need there thanks...

Stuart

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abmartin
SSD900 Darmah
Posts: 357
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Location: New Brunswick, Canada

Re: Request for advice reference slipping clutch

Post by abmartin » Fri Sep 13, 2013 8:17 am

Hi Stuart,

Nice that you could do the Manx Grand Prix parade lap. I'm jealous.

The clutch adjustment isn't complicated. The outer plate screws are tightened fully and then adjusted slightly to get an even rotation of the plates when the motor is kicked over without spark plugs. Adjusting the centre screw will give you enough play so that the actuating lever doesn't bind against the engine case. There is also the two cable adjusters, one on the motor and the other at the handlebar lever for finer adjustments.

While you're into the clutch area it may be worth replacing the shift lever centering spring located behind the clutch basket. It's not a question of if it will break, it's when. You can then find that the bike won't shift gears. The gear lever adjustment after replacing the spring can be a little fiddly but nothing too serious.

Cheers,

Bruce
1979 900SS
Fredericton, NB
Canada

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Craig in France
Cagiva Elefant
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Re: Request for advice reference slipping clutch

Post by Craig in France » Sun Sep 15, 2013 9:01 am

abmartin wrote:I took a look at my Ducati Tuning book by Stephen Eke. He maintains that the 450SCR clutch springs won't work on left-hand gearshift models because they have revised clutch baskets with longer springs.

Hi Bruce,

I suspect Steve Eke's statement there may be a bit too 'all-embracing' ... :shock: . Checking thru the parts books that I have here shows:

1. Up until the 1979/80 900SS and the 1980 SD, the same clutch springs, part number 0400.16.550, were used in the twins, regardless of left side or right side shift.

2. After that date, the spec changes: to the 450SCR springs, part number 0480.**.***

(Not surprisingly, during this time,the same clutch basket is used on the twins: part number 0759.16.814).

3. According to Ian Falloon, the new clutch basket dates from 1981, specifically from engine number 091267. I don't have a 1981 parts book to confirm this; but certainly that is what the 1982 900MHR book shows: springs are now 0799.**.*** , clutch basket also 0799.**.***

So, given that Stuart's bike is an early one, there's a good chance that he has the standard springs; so a swop to 450SCR ones may yet help.
abmartin wrote:My '79 SS has Surflex plates, I don't know if this was standard at the time
Surflex was the OEM.

Ciao

Craig

Cheese
Cucciolo - the Lil Pup
Posts: 14
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Re: Request for advice reference slipping clutch

Post by Cheese » Thu Sep 19, 2013 8:52 am

I read an article from a DIOC news letter from the mid eighties which described modifying a bevel twin 900ss motor to (GASP)belt drive for racing. He mentioned clutch slip and talked about drilling several holes in each steel plate which apparently cured it.

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