How about a Desmo Norton?
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Desmodromics were invented when valve train technology was rather simple as a way to overcome valve float and increase rpm and thus horsepower. Adding Desmo valves to a Norton would only expose the next weakest link-the crankcases and crank design. Of course, these have been re-hashed repeatedly over the years.
With modern valves and springs race motors (F1 and MotoGP) have attained 15-17K rpm without turning into grenades, thus making Desmo obsolete. Ducati hangs on to Desmodromics and the 90 degree V to sell streetbikes and have advanced their design quite a ways over the years. With the new rules in MotoGP, they might actually get some podiums this year.
The only valve adjustment approaching Ducati's Desmo in time, complexity and expense is a Honda Vtech V4. $500 valve adjustments are a bit rich for my blood.
With modern valves and springs race motors (F1 and MotoGP) have attained 15-17K rpm without turning into grenades, thus making Desmo obsolete. Ducati hangs on to Desmodromics and the 90 degree V to sell streetbikes and have advanced their design quite a ways over the years. With the new rules in MotoGP, they might actually get some podiums this year.
The only valve adjustment approaching Ducati's Desmo in time, complexity and expense is a Honda Vtech V4. $500 valve adjustments are a bit rich for my blood.
I don't see anything, and can't get a link out of it to go view anything...
Doug Hele tried desmo with wanx nartons in the late 1950s,
and found if you can't rev it hard enough to get any benefit, there was no benefit.
What has changed..... ?
EDIT Update - the video has become visible.
Desmo has been around since about circa 1900ish.
Look how many production engines have actually used it.
And even Duc had non-desmo versions of the same thing, mostly...
Doug Hele tried desmo with wanx nartons in the late 1950s,
and found if you can't rev it hard enough to get any benefit, there was no benefit.
What has changed..... ?
EDIT Update - the video has become visible.
Desmo has been around since about circa 1900ish.
Look how many production engines have actually used it.
And even Duc had non-desmo versions of the same thing, mostly...
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Cool that chevy desmo makes as distint tappet-ty sounds we all know so at least wouldn't lose that Commando sonic signature. Would desmo allow more radical profiles vs push rods? - as current valve trains don't limit Cdo rpm before friction does. Does desmo have less friction than cam on tappet push rods? Would it last longer in adjustment?
Duc desmos were renowned for their fierce valve opening and closing actions, so....
As for the rest, who knows, haven't seen the Commando desmo blueprints yet.
But if its not at least 1500cc its not even in Triumph Thunderbird territory yet.... :mrgreen: :mrgreen:
As for the rest, who knows, haven't seen the Commando desmo blueprints yet.
But if its not at least 1500cc its not even in Triumph Thunderbird territory yet.... :mrgreen: :mrgreen:
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Ugh no kidding so I'm starting with 920 cc and variably adding at least 50% more cc of mix in next Peel. If turns out I like excessive power/wt more than Peel then I'm going for the 1/2 Corvette V4 American Beef that this desmo demo is a bolt extra before boost and special fuels. I'd still retain and isolastic mounting of course.
[video]https://www.youtube.com/watch?v=6K0TOcGRknc[/video]
[video]https://www.youtube.com/watch?v=6K0TOcGRknc[/video]
Rohan said:
Years ago there was a comparison of a BMW flat twin and a Duc Testastretta. The BMW had more aggressive cams than the Duc.
F1 engines don't have dedicated valve springs anymore BTW, they rely on pneumatic springs for almost two decades by now. Speaking of F1 and desmo .... the text is pretty much BS however: The reason why at least two engine manufacturers played around with Desmos was an idea voiced by the FIA to ban pneumatic springs. Desmo was one topic afterwards, at least one other manufacturer build an engine with sleeve valves. The engines were en par with current designs however pneumatics were not banned but poppet valves were made mandatory so none of these engines made it further than onto a dyno.
Tim
Tintin said:
Do you know which BM ?
I have a Duc head and some desmo cams, and was looking at the possibility of fitting it to a cammy Norton
(its almost a bolt-on fit, both 86mm bores bevel drive 2 valves, who copied whom ??).
Without having degreed it, desmo cams look pretty wild. Valves are quite small though, they kept them light (?).
The Testastretta is 4v head, could probably user milder timing. ?
Mercedes F1 cars were desmo in the 1950s, and I think I saw that Peugot were back in the early 19teens.
There are hundreds of desmo patents, Pa Norton took one out in the 1920s.
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Tintin said:
My BMW 1000 race bike is rev limited to 8000 and still pulling with a stock cam, my Bevel Darmah would probably not like going past 7000.
Local bloke built a Desmo Norton here some years ago.
[video]https://www.youtube.com/watch?v=LLp5uMRuZJU[/video]
72Combat said:
Is it a desmo ??
There is that famous story of Paul Smart, riding the then new factory duc desmo 750 at Imola.
The story goes that he didn't really want to be there, and "he held it flat in 3rd gear down the back straight,
and after a few laps he decided it wasn't possible to blow it up, so he finished the race, and won".
And became a hero, although he didn't tell this story until years later.
He married Barry Sheenes sister, and she got him the ride - needed the money !
72Combat said:
There are a few around, when you count them all up.
Dunno how it can be the only one in the world.
Duc cylinder head is a near bolt-on fit too, but the finning (and cambox) look a bit wrong....
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The main advantage of the desmo is not increased engine speed, not to prevent valve float at high engine speed; the advantage is that the opening follower can be opened much quicker with out "throwing" it (and the valve) off the cam and into destructive "float," so it doesn't "bounce" or crash back onto the cam. The closing follower checks, and holds, the lifting follower close to the cam when it tries to fly. Now the cam's shape can be optimized; it can be almost square in shape, as opposed to pointy egg shaped, and less time/degrees of crank rotation can be spent in opening and in closing while more time/degrees can be spent at full open - holding the open for a long time along that flat top of the grind.
So, the big advantage of the desmo is in breathing; at the same lift, more time wide open, and, if you need more lift, you can have it . . . and . . . . it can be had with a less pointy cam. Flat topped and tall - that's the ticket.
Advantages are greatest with a two valve head, diminishing returns with a four valve head.
Thanks Jim, a desmo would be fine, no need to spin our engines to get its advantages, although that would be the temptation.
So, the big advantage of the desmo is in breathing; at the same lift, more time wide open, and, if you need more lift, you can have it . . . and . . . . it can be had with a less pointy cam. Flat topped and tall - that's the ticket.
Advantages are greatest with a two valve head, diminishing returns with a four valve head.
Thanks Jim, a desmo would be fine, no need to spin our engines to get its advantages, although that would be the temptation.
Rohan said:
Not really, must be about 15years ago when the Testastretta came out and there was a fairly new BMW flat twin design back then but my memory is very vague there. It was not a special engine, that was the surprising thing. And the BMW was a 4V, the R series got that feature in the 90ies.
I really only remember that the harschness of the ramps was the other way round than expected.
Tim
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