Cams n valves n stuff

Fast Eddie

Fast Eddie

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Last week I went on a Ducati factory tour.

Really interesting to see inside these motors, the pistons are such a huge diameter, and yet SO short, it’s incredible,

They had a sectioned engine that turned over via an electric motor. You could see the Desmo valve gear in operation.

The exhaust cam was fascinating, it appeared to have what I can only describe as slow motion valve bounce!

The exhaust valve opened and closed as normal, but then opened and closed again, just a little bit.

It wasn’t an error, you could see the cam had clearly been made to do this.

Does anyone know WTF it does this for ??

Allowing in a little more unburnt exhaust gasses that are pushed back in via a pressure wave is all I could think of... anyone know any better...?
 
in the small engine world it is done as a compression release for starting. the second event is so small it it has no real effect at running speed.
 
Briggs engines have this on their cams as its a compression release at low revs, if the tappet clearance is set wrong the feature is lost and the starter cannot turn the engine over so check the tappets before buying a new starter. As Bill says as the engine speeds up the compression is restored.
 
I have been led to believe these new(ish) super short stroke Dukes are so touchy and sensitive to cam timing/ignition timing/fuel mixture control that they would not successfully run without a computer monitoring and continually varying these parameters - blindingly quickly.
Very, very impressive but, I'm afraid, not for me.
 
This was after the exhaust stroke, so no compression to release. As far as I could tell / can recall, it was a fixed element to the cam, ie not for starting or low rev use only.
 
the small bump on the exh cam lobe is well past the exh. stroke and is on the compression stroke. as komando stated it also makes valve clearance critial.

Fast Eddie said:
This was after the exhaust stroke, so no compression to release.
Click to expand...
 
bill said:
the small bump on the exh cam lobe is well past the exh. stroke and is on the compression stroke. as komando stated it also makes valve clearance critial.
Click to expand...

Not on the Ducati Bill, the small extra lift is immediately after the exhaust valve closes, and is only a tiny blip. I can’t see any compression having built up in that time.
 
robs ss said:
I have been led to believe these new(ish) super short stroke Dukes are so touchy and sensitive to cam timing/ignition timing/fuel mixture control that they would not successfully run without a computer monitoring and continually varying these parameters -
Click to expand...

I’ve no doubt that’s true Rob, but I’d also imagine it’s true of every other new performance bike currently on offer.
 
Fast Eddie said:
It wasn’t an error, you could see the cam had clearly been made to do this.

Does anyone know WTF it does this for ??

Allowing in a little more unburnt exhaust gasses that are pushed back in via a pressure wave is all I could think of... anyone know any better...?
Click to expand...

Probably done to confuse the competition, they must have a sense of humour.
 
Nigel, while you were in the Ducati factory, did you see the Paul Smart Imola Ducati ? My friend used to own that bike. When I was racing in the early 70s Ken Blake was riding it. My friend sold it to I think Brooke Henry in Western Australia for about $3000 who then sold it back to the Ducati factory for a very big number. When I visited that factory, I was impressed by the way they did so much with so little. I thought it would have been a much bigger factory.
 
Incidentally, in the cylinders of the RD400 Yamaha two strokes, there is a small hole drilled from the exhaust port to a point in the cylinder wall, about an inch lower then TDC. Apparently, it is a pressure release supposed to stop 'surging'.
 
acotrel said:
Nigel, while you were in the Ducati factory, did you see the Paul Smart Imola Ducati ? My friend used to own that bike. When I was racing in the early 70s Ken Blake was riding it. My friend sold it to I think Brooke Henry in Western Australia for about $3000 who then sold it back to the Ducati factory for a very big number. When I visited that factory, I was impressed by the way they did so much with so little. I thought it would have been a much bigger factory.
Click to expand...
Ducati gave that bike to Paul Smart and he still owns it.
 
Al, yes, the Paul Smart Imola Bike was there and looked fabulous!

And yes, I was also expecting a bigger set up in general.

Nice to see the passion though. I went with two friends, two of us on Ducati’s and one on an MV. Man on the gate shouted “only Ducati” whilst shaking his head and wagging his finger at my MV mounted mate, they made him park out on the street whilst we Ducati riders got ushered in like VIPs !!

We didn’t take the piss though... honest...:D
 
oldbeezer said:
Ducati gave that bike to Paul Smart and he still owns it.
Click to expand...

Interesting, tune definitely had ‘it’ there on display. Maybe PS owns it and loans it to them? Maybe it’s not real? I dunno.

I do know that PS has a PS replica (as in the 2006 LE PS replica) that the factory gave him, I chatted to him with it at Cadwell Park a few years ago where he was showing everyone else the way around the circuit on it!
 
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