Hot day=Hot clutch

[Muzz350]

It was a hot day today and I rode to work on my 350 ducati. It was fairly heavy traffic and the play in the clutch cable got more and more as I went along. I eventually adjusted the lever to take up the slack while sitting in the traffic. When the bike cooled down the cable got tight again. Can someone explain to me what is expanding and contracting to cause this. The clutch plates are the original ones with only about 7000km on them but are about 35yrs old. Should I replace them and maybe the springs? Would modifying the clutch in other ways improve it eg heavier springs , thicker plates, lighter etc? Are new plates made of better/improved materials these days?
Thanks
Muz

[LaceyDucati]

Hi Muz
When the clutch gets hot the plates expand and the clutch pack gets thicker. As the pushrod assembly passes through the clutch pack, extra clearance is added to the push rods and hence the lever goes slack. Then if you continue the clutch drags more due to not clearing, gets hotter and eventually drives you into the car in front if you can't get in neutral. Which of course you can't as the clutch is dragging! When the clutch cools down the freeplay will then be returned to before. Unless you have spun the clutch then the 1mm steel plates can "pop" like a bell washer, then it will always drag.

Fitting heavier springs won't improve things and will probably make it worse! The heavier springs will put more load on the cable etc, leading to more stretch and less lift at the clutch pressure plate. With less free space between the plates the clutch is more likely to drag and lead you to a hot clutch!

One thing you can do is fit 2mm steel plates. This is done on the 5 speed models by using one less steel and friction and spacing the clutch drum 1mm to maintain the original spring pressure. This mod will help as you have one less gap in the clutch pack, which means the remaining gaps are wider gaps ( lift divided by the amount of gaps). With more clearance between the plates, there is less likely to be drag. We have been using this set up in race bikes since the early nineties with no problems in 250's or 350's. With 450 racers we made longer clutch baskets and hubs to revert to the 6 and 7 plate set up still using the 2mm steels. For road use we have not had any problems with the 5 and 6 plate set up in 450's. The 2mm steels also have the advantage of not belling when you spin the clutch off the line in a clutch start race.

Modern materials are marginally improved, but if your frictions are in good condition I would not be to concerned about their age. The main reason for replacing friction plates would be if the material was burnt or torn, but this would be giving you clutch slip problems rather than dragging. Check all the steels for flatness and make sure they are not "popped".

One other thing to check is the thread in the pressure plate, as some of these are welded skew meaning the adjuster screw is not true to the plate face. This will cause the clutch to lift skew and also lead to possible dragging. As will odd length clutch cups/springs.

Hope this helps

Best Wishes Nigel

[Muzz350]

Thanks Nigel
I could not see how expanding plates made the cable looser but your explanation makes perfect sence and you are right about creeping forward with the clutch lever in while desperately trying to find neutral.
I'll try the 2mm plate remedy and check the thread is centred and the steels are flat.
Many thanks
Regards
Muz

[machten]

Nigel,

Let me also add my thanks for you taking out some time to provide this detailed response. This is of particular interest to those of us in the antipodean climate.

Many thanks,

Kevin

[DaveSmith]

Would the 2mm plate thing work on a bike that gets used in heavy traffic? Or is it mostly for racing? I've got a 65 nc that in my spare time I'm riding round the world on.

[DewCatTea-Bob]

" Would the 2mm plate thing work on a bike that gets used in heavy traffic? "

____ Yes, of-course,, and especially-so in such extra stressful case (when the clutch is more-often repeatedly used) !
__ The 200 motors only employed 6 friction-plates and the 7th-plate was added beginning with the 250-motor just for logical good-measure - (a resulting 17% increase in clutch-plate contact surface-area, intended to more equally cope with the 22% increased engine-capacity), but the addition of the extra drive & driven plate pair, merely helps assure that the clutch doesn't slip while under full-throttle (once the clutch has been allowed to be fully engaged). _ So for a 250-motor that's not under constant stress of full-throttle torque, the extra plate really isn't needed,, and-so Ducati probably shouldn't have added the 7th-plate pair until the 350-motor was designed.
But when the 7-plate clutch replaced the 6-plate version, Ducati then SHOULD've also began employing weaker & easier to work clutch-springs to go-with, (until the w-c.design [with it's improved lever-arm leverage] became produced,, AND at which point, they should've by then also began the use of thicker driven-plates [with a deeper clutch-basket] ).


Dukaddy-DUKEs,
DCT-Bob

[DaveSmith]

Thanks! I've had good luck with Bobs with this Duc.

[DewCatTea-Bob]

" I've had good luck with Bobs with this Duc. "

____ What "Bobs" have you had with your Duke ?
__ BTW, are you the same world-traveling fellow who once mentioned to me that he may possibly one day pass-over the Mackinac Bridge ?
____ Anyhow,, just in case you missed the link I added to the other related-topic thread (which you've also posted within), here follows a link to a thread with related-info for helping to assure proper working function of the clutch-operation. ... viewtopic.php?f=3&t=1156&p=7861&#p7856


Hopeful-Cheers,
-Bob

[DaveSmith]

Bob Dumma (who let me stay at his house for weeks after the tank cracked pouring gas down my leg in a brush fire). Bob Brown. DewCatTea-Bob for some great advice on the clutch.

Yes, I'd love to make my way to the Mackinac Bridge. I'm not sure if I'm going to ride across the US this spring or not. I might go south through Austin and New Orleans, but I also have friends in Denver and Chicago I'd like to visit.

Riding round the world in my spare time (aka, can't afford to do it all at once).

[DewCatTea-Bob]

" DewCatTea-Bob for some great advice on the clutch. "

____ I didn't expect you to respond so QUICKLY ! ... I chose to edit my posts (above), and was possibly in the process of doing-so when you happened to log-in & place your response-posting.
So now I'm just checking to make-sure you've noticed my now finished-posts.

____ David, do you happen to recall how you & I once communicated about you possibly stopping-by over to my-place if you ever happened to travel over the M.Bridge in Michigan ?
I can't remember if our contact was made through this w.site, or some other means,, as it was over a couple of years ago.


Hopeful-Cheers,
-Bob