Clutch Drag…

[Dukedesmo]

Sounds like the clutch pack is too thick to me.

From memory, I think they state 38.5mm is the correct overall thickness, including all frictions and plain plates but I would advise that is the maximum as I find at that thickness that there is likely to be too much drag, making finding neutral tricky when the engine is running and bike stationary.

I set mine at 38mm or even a tad less, do this by replacing one or more of the 2mm plain plates with 1.5mm plates. Tip; if you have enough 1.5mm plates you can often 'juggle' things around enough to get an extra friction plate in - I have in both mine but I also only fit one plain plate at the bottom of the pack rather than the 2 normally fitted (always use a 2mm there though). This gives a better clutch action and longer life IMO but, obviously you can only do this if you have an extra plate (some 'kits' are supplied with 1 extra).

With regards to the correct pack thickness and obtaining an easy neutral, when you've assembled the clutch, before starting the engine - pull the clutch lever fully in and you should be able to rotate the clutch by hand, if there's any drag you will feel it. I like to get mine free enough that if I 'spin' it (clutch lever fully in) it will rotate freely and even over-spin a little once I let go, this way it'll be free enough for easy neutral. If it turns but drags so that when you let go after a 'spin' it stops dead then chances are you will have problems selecting neutral at a standstill.

As for being too thin a pack, if this is the case you might get slippage but I have never experienced slippage (other than when I had an oil leak through the pushrod oil seal on my 916) due to a worn clutch even when very worn/thin as the springs are strong enough to clamp the clutch tight - it might help that I have stainless springs which I think are stronger than standard but for a time I ran my 916 with just 4 springs (makes a lovely, light clutch) and still never had any slippage.

As mentioned above, I never use the dished plates either as I see no benefit in doing so but this divides opinion with many telling me I'm mad/wrong/stupid but I have never had a problem due to this and both of my Ducati dry clutches are smooth, progressive, slip-free and able to find neutral at standstill so, I'm claiming victory.

[Dukedesmo]

To add to the above, whatever the clutch pack thickness and however tricky finding neutral maybe, it will get better as it wears.

[Mr Gazza]

Originally Posted by Leamreject

.. and with a medium dry emery rubbed each face a few times on a flat surface, nothing significant as you would if doing brakes.

I would not.
I don't touch brake pads or clutch friction material with anything other than clutch and brake cleaner and a toothbrush.
The metal and friction material wear together to a near 100% contact area for best performance. Any abrasive interference reduces that and will require further bedding in, not to mention the possibility of embedding carborundum or other particles in the friction material.

Dust is the worst enemy of a dry clutch. Is it possible that some dust remains in the clutch from the emery operation? A wash with clutch and brake cleaner is all it should need. I give mine an annual bath.

Are the slots in the drums worn into little "serrations" where the plates sit? and do the tangs on the plates have any burrs? Those could hold the plates a bit, or tip them, as they will almost certainly have gone back in different slots.

I know nothing about slipper clutches, but I can work out that there is some sort of automatic clutch actuation involved which must have a starting point. Is there adjustment on the slipper mechanism?

[Nasher]

Originally Posted by Dukedesmo

Sounds like the clutch pack is too thick to me.

It certainly sounds that way Dd.

Although last time I had clutch drag and hard to select Neutral issues with a clutch I rebuilt I had to make the pack slightly higher to solve it.
And No I can't really explain it either.

I'm not sure what the story is with Slipper clutches.
The used one I brought months ago to have a play with is still in it's box ready to be fiddled with.

[350TSS]

You could check whether the clutch hub nut is tight, the clutch will drag if it loose as the movement in the clutch push rod against the pressure plate is lost if the hub moves with the plates

[Leamreject]

Originally Posted by Nasher

It certainly sounds that way Dd.

Although last time I had clutch drag and hard to select Neutral issues with a clutch I rebuilt I had to make the pack slightly higher to solve it.
And No I can't really explain it either.

I'm not sure what the story is with Slipper clutches.
The used one I brought months ago to have a play with is still in it's box ready to be fiddled with.

That would be odd as it was fine before I stripped it and I haven’t added anything to the existing clutch pack, putting them in different slots might have contributed to that so once measured I might need to rotate them to change the tolerance perhaps. I will measure it when I get it apart and let you know my findings.

You’ve all given me ideas to work with, very valuable… thank you

[Dukedesmo]

Originally Posted by 350TSS

You could check whether the clutch hub nut is tight, the clutch will drag if it loose as the movement in the clutch push rod against the pressure plate is lost if the hub moves with the plates

Worth checking, also that the petal shaped washer has not eaten into the hub - this happened on my 916 and whilst the clutch was still working fine there was enough play for the clutch pack to move outward enough for the spring caps to rub against the open cover.

[Nickj]

Originally Posted by Mr Gazza

I know nothing about slipper clutches, but I can work out that there is some sort of automatic clutch actuation involved which must have a starting point. Is there adjustment on the slipper mechanism?

Simple back-torque limiter clutch, levels the torque between the motor and driven wheel. Usually a set of 5 or so pairs of ramps _//_ that when you put lots of torque through them slide. The sliding turns the rotation into movement along the axis of the clutch that can be used to push the plates apart a little. Great if you stomp down the gears, the motor doesn't over rev (so much) and the rear wheel doesn't hop (so much) or lock up. Really not fantasticly useful on a road bike but goes with the 'race derived technology' that gets used to advertise bikes, very handy for track days though.
Can be a right royal PIA to get working right.
The 748R has one but it's really crude and was only fitted to homolgate slippers into the ducati race bikes of the time. Besides ii only takes a little finesse to rapidly run down the box as the ratios are so close to start with.

If you have to start grinding away at the clutch with emery or filing the clutch basket where the tangs have made anything more than a smalll polished area then it's a sign from above that it's not well and a visit to your local parts emporium is indicated.

[adie851]

As Slob states in his post...the stack height of the plates is quite critical...sounds like you've put it back differently to how it came apart.... ?

[adie851]

Another point previously stated is that I wouldn't use any abrasives on clutch plates...especially a dry clutch...just brake cleaning fluid..which evapourates once the part has been sprayed ....to remove any dust build up ..otherwise its a new set of plates I'm afraid....good luck ..let us know how you get on....

[Leamreject]

All sorted, stripped it down several times now, the pack size is 38.5mm so within tolerance. However, the pack consists of 9 discs and 9 clutch plates not 8 as expected. No dished or convex types.

The odd thing is, that I don’t actually know what corrected it, after watching several youtube clips and other bits on the interweb without success, I eventually added a 4mm insert to the slave because I wasn’t getting enough movement, well that gave me no drive at all, so I went 3mm which appeared to work but on riding it was slipping.

I knew then that a spacer wasn’t the issue because fitting a 2mm one just wouldn’t make sense. However, on removing the 3mm spacer the problem went away which has really confused me now. I can only assume that something must not have been seated correctly and on fitting the spacer the additional movement settled something… very odd but now it’s working as expected.