Ducati 888 SOLD

Tippie said:
All the bevel demos had some sort of spring, singles and v twins.
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You're right Lee. I remember seeing hairpin type springs in the singles years ago, but don't recall seeing them more recently in my MHR Mille. But I checked the parts diagram and they're there. I guess that means my long term memory is better than my short(er) term.

I was told years ago by a Ducati guru that the springs are there to ensure the valves close fully in the event that the closing valve clearance loosens up a bit. It's supposed to be zero clearance, but will open up a bit as things wear. If the valves aren't fully seated when closed, it would make starting quite difficult.
 
I was told that they often wouldn't idle without springs inserted, and although it didn?t make sense to me never tried it out. I know of racing bikes that had dispensed with them. They were so light I couldn't imagine the power gain to be relevant. A mate racing a single was told by an Italian racing team to only use spring heads, and never use a demo single for racing, also sounds weird to me, but they had lots of experience.
 
Makes sense to me that they won't idle without valve springs. When an engine is producing power, the gas flow and cylinder pressure will keep the valves closed. But at start-up and idle, not so much.

I've not heard that a valve spring head is preferable to desmo for racing. MotoGP bikes are desmo so it sounds a bit weird to me too. Especially considering the experience of a mate of mine who owned an 860 GT with valve spring motor. He bought it new in about 1975 and within the first 10,000 km it had eaten a couple of sets of camshafts and rockers (not to mention big end bearings). He took it to Bob Brown in Melbourne who rebuilt the motor. He reckoned the valve spring pressure was way too high, so he took out the inner set of springs leaving just the outers. Bike still revved fine to the red line and didn't wear out the cam lobes. Seems Ducati were better at making desmo engines than valve spring type. They should have stuck to what they were good at.
 
They were just referring to singles. Yeah 860 GT I knew of more than one that dropped valves when almost new so not surprised to hear that. Bob Brown taught me how to do desmo valve shimming. Destroyed cams and rockers are often caused by no valve clearance so they drag across the whole base circle, preventing proper oiling. That motor probably ended up with the valves closed up due to the springs. Some Hondas in the early '80s had a bit of play in the cam bearings, people who liked a tight feeler gauge caused the same problem.
 
Tippie said:
I was told that they often wouldn't idle without springs inserted, and although it didn?t make sense to me never tried it out. I know of racing bikes that had dispensed with them. They were so light I couldn't imagine the power gain to be relevant. A mate racing a single was told by an Italian racing team to only use spring heads, and never use a demo single for racing, also sounds weird to me, but they had lots of experience.
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To properly seal the valves at standstill/idle on a desmo without the helper springs, you would need to load the rockers, less than zero clearance, so to say.  We all know that doesn't work, not for long at least, so the springs are required for a good seal for start up.  Once the thing is running, they have no further influence.

The springs are a bugger to fit, even with the factory tool, on the V/L-twins.  Can't remember how it went on a single, been too long ago since I had a look inside one of those.

I always wondered what the hype was about concerning the desmo valvetrain.  Certainly nothing for the average backyard bodger, but after setting up an entire engine with bevel gear spacing and all, I found it a piece of cake.  Simple engineering rules apply, nothing really special.  I've found several incorrectly set up desmos, performed by "reputable experts".  Took about 40 kicks to get the bastards to even cough and splutter.  One even sounded like a clapped-out Lav triple!  After only a bit of basic maintenance, the 2-kick start returned.  I could live with that... but they'll never be my cup of tea.

piet
 
Dellortoman said:
I've not heard that a valve spring head is preferable to desmo for racing.
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You may find the opinion of Nigel Lacey pertinent here.  Just to be clear: he's talking about the singles.

"My conclusion after 30 years of working on these bikes and 21 years in business is: I would always choose a spring valve head over a Desmo for racing or performance.

I have built various successful race singles with Desmo heads.  However my professional opinion is that this was in spite of being Desmo, rather than offering any advantage! The same cam profiles can be run with valve springs and, without the closing rocker, the valve guide can be positioned higher, creating a higher, better flowing port.

I do not buy into the valve spring losses as, for racing at full tilt, the inertia in the valve will largely cancel out spring load. The inertia in the valve still exists in a Desmo and it has to change direction the same, so the loads are still there. This can be observed by the hard life the collets (keepers) and valve grooves get in a Desmo race engine.

I hasten to add all my race Desmos had either no springs or the twin snail springs. My experience with this was they both performed the same with regards to wear issues or performance."
 
Dellortoman said:
<snip>  He reckoned the valve spring pressure was way too high, so he took out the inner set of springs leaving just the outers.
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And he was right  ;).  As I'm sure you know, Cam: it's an abiding mystery why Ducrappi thought it necessary to fit twin springs to the early 860s ... ???
 
Dellortoman said:
Especially considering the experience of a mate of mine who owned an 860 GT with valve spring motor. He bought it new in about 1975 and within the first 10,000 km it had eaten a couple of sets of camshafts and rockers (not to mention big end bearings). He took it to Bob Brown in Melbourne who rebuilt the motor. He reckoned the valve spring pressure was way too high, so he took out the inner set of springs leaving just the outers. Bike still revved fine to the red line and didn't wear out the cam lobes.
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Unless it came with shit cams and the replacement cams were not. Not exactly proof that lighter springs solved the problem as most all springer 860's worked just fine.

Jim
 
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