Witt DMC 2 rant

[Dellortoman]

Gear driven cams (as bevel Ducatis are) are a more accurate and bullet-proof solution to making camshafts rotate. They don't have chains or belts that need tensioning adjustment and regular replacement. As chains/belts wear and stretch, the valve timing will retard slightly. Also, there's always the small risk that a belt or chain will break in service, with catastrophic results. Breaking a cam timing belt at 10,000 rpm on a 4-valve Ducati doesn't bear thinking about. You'd have to sell your children to fix it.

I prefer gear primary drives for the same reason, which my Ducati also has. I lose on both counts with the Laverda 

Most of the more exotic race engines have gear driven cams. Manx Nortons, Honda RC30 and Moto Guzzi V8 come to mind. I dunno what today's crop of MotoGP bikes have, but I'd expect gears to be in the majority of engines.

The advantage of belts and chains is that they're easier (and therefore cheaper) to build. In the case of primary and final drives, chains also offer the potential for easy ratio changes (not a good idea for camshafts!)

Cheers,
Cam

PS: Bit of a thread hijack. Good thing there are no thread police on this forum

 

[Scrumpy]

I have used "Vaseline" on my electrical connections for years without any problems.

Scrumpy

 

[Xav]

Bevel = couple conique (Purple rectangle)

Desmodromique (Round Black)

Biseau = chanfrein (you are right)

Appel de phare

Xavier

 

[Xav]

... Miracle

Here are the photos

 

[lemonjelly]

Thanks Cam appreciate the enlightenment.

Shaun

 

[conrad]

I like them windows that some ducati bevel riders have done.

 

[laverdakeith]

I like them windows that some ducati bevel riders have done.

  Also dead handy for watching the remains of your big end bearing float past....

  Keith

 

[bob]

Shaun, the cons of bevel drives are mainly high manufacturing costs and the fact that they tend to need careful setting up at service intervals, usually with some some form of shimming. They also make a bit of a whirring noise....
Cam will correct me if I've got the first part of this wrong but as I recall not all bevel driven Ducatis are desmodronic and not all desmodronic Ducatis are bevel driven.

 

[sfcpiet]

Cam will correct me if I've got the first part of this wrong but as I recall not all bevel driven Ducatis are desmodronic and not all desmodronic Ducatis are bevel driven.

Matter of fact, only the "sportiest" bevels got the desmo gizmos...... probably couldn't wind valve springs properly in Bologna , so Dr.T. needed to come up with a (costly?, for sure..... needless?, probably!) solution.  There were lots of high-revving OHC/DOHC small capacity italian bikes at the time that coped without the need for desmodromic valves.  A solution looking for a problem ???

piet

 

[Xav]

I like the technic of the systems desmodromic. The setting is interresting to perform (sitting ?)

The Bevel is d?liquat to sitting (r?gler)

These (2) both solutions are not necessarily rational, but if we can say about this moving mechanical parts, me, I would say it's beautiful

Xavier

 

[Dellortoman]

Shaun, the cons of bevel drives are mainly high manufacturing costs and the fact that they tend to need careful setting up at service intervals, usually with some some form of shimming. They also make a bit of a whirring noise....
Cam will correct me if I've got the first part of this wrong but as I recall not all bevel driven Ducatis are desmodronic and not all desmodronic Ducatis are bevel driven.

Correct on all counts Bob.

Clearance between all four pairs of bevel gears has to be set by adjusting the axial position of each of the gears with shims. But unless you're doing a complete engine re-build, there's no need to alter the factory setup. On my bike, the music from the Conti exhausts masks any whirring noise. 

The first belt driven Ducati was the 500 Pantah in about 1980. They were still making bevel engines up to 1985, so there was a few years of overlap of belt and bevel on the production line.

I agree with Piet too. Desmo valve operation is a bit un-necessary, especially for a road bike engine. It's also a pain in the arse to do the valve clearances (a head off job with the bevel engines). But it's interesting, and once set up properly it's very reliable. It eliminates any risk of piston/valve entanglement if you miss a gear.

Cheers,
Cam

 

[Scrumpy]

Not Witt but interesting all the same. This bike displays a lot of nice features.
Scrumpy

 

[Grant]

For sure there is a lot of innovation these days with dialling in electronics into motorbikes, but I can't help get the feeling that the golden age of mechanical innovation in the internal combustion engine was in the early 20th century.
Today with greater precision and better metallurgy things can move forward, but back then everything was tried.
I think Triumph had a patent on oval pistons in the 20s, as opposed to the oval bores they gave us with the T150...
Even desmo had been around since the first world war (was it Mercedes?). Taglioni did not invent it, just applied it to bikes.

 

[Xav]

Absolutely agree with Grant. And the picture of Scrumpy is a perfect example. There was even a cantilever suspention. would be ?

These old mechanics are ingenious and "logical"

Xavier