Triumphrat

The Jerk · 05-01-2008

I don't know about dry-clutch Ducatis but dry-clutch BMW bikes do this too. If it's on the center stand and you release the clutch lever with the trans in neutral, the rear wheel will slowly spin.

The reasons above for why this happens are correct. On a bike like the BMW, there is no sharing of engine oil and transmission oil but you still get the same effect because as the engine drives the tranny's input shaft, it gets all the gears in the transmission spinning around in that nice think transmission oil. That causes some rotation of the output shaft just through the movement of the fluid even though neutral is engaged. That's why you can stop it with your hand. The colder and thicker the trans oil, the faster the rear wheel will spin.

Manual transmission cars will do this too, but you only see it if you have both drive wheels off the ground simultaneously. First noticed it on an old VW I was working on. But if it has an open differential, only one of the drive wheels will turn. If you grab that one to stop it spinning, the other one spins instead

ohiorider · 05-01-2008

Quote:

Originally Posted by modre

actually no.
the cold first gear cluck is (clutch disengaged) plate friction and thick oil, (old kick start you had to do a kick with the clutch disengaged to break the plates loose)

but the rear wheel spin (clutch engaged in neutral) is there's some friction between the shafts and gear bearing surfaces and perfectly normal...it's like stirring a spoon in liquid drives the liquid crazy.

I knew I was going to get called on my response as soon as I posted it, but I thought I'd leave it simple, ie, cold, thick oil causes the problem, whether it causes clutch plates to stick together slightly when cold, (causing the clunk upon gear engagement) or whether it causes the gears and other revolving parts in the tranny to tend to 'pull' on each other in neutral until the oil warms up and thins out.

But to be specific as to what causes each individual condition, you, sir, are correct.

Bob

fastbike · 05-01-2008

They (dry clutch ducatis) do the same until you stop the wheel. The spinning won't restart however. The clutch plates will stick just a little. This is why you often get a little jerk when you put the bike in gear.

Quote:

Originally Posted by vanson1200r

I think the reason why the wheel will turn is because the clutch plates are so close together and they are submerged in motor oil and there is some drag as one part of the clutch spins and the other does not. I don't think dry clutch Ducatis do the same thing.