How about a Desmo Norton?

So we need desmodromic valves on a road bike ? I had the impression that you guys were trying to make commandos the equivalent of air cooled Ducatis at half the price. You'd be better off with side valve Harleys.

You seem to be all over the place, so why can't we follow a logical line of thought now and then....

And there still is a Norton Co producing pushrod parallel twins as NEW motorcycles,
so Norton production is not dead yet.

And Pa Norton does have that 1920s desmo patent application in his name...

Hopwood and Hele were thinking "Desmo" back in the 50's
Now all we need is someone to solve the crank/crankcase issues.

Since when have patents been international ? And why would you need desmodromics in a slow revving motor ?

Resolve the crank/crankcase issues, and there would be no need for a slow, or low revving engine.
A Desmo head on a shortstroke engine might just be the ticket
Just saying Hopwood was thinking about it long ago.
Perhaps if he had been provided the tooling and funding, it would have become a reality.

acotrel said:

And why would you need desmodromics in a slow revving motor ?

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As the previous discussion pointed out, if you can remember that far back,
getting the valves quickly open and closing with desmo gives quite a pronounced gas flow benefit.
i.e. more power.
Shirley even understands this.....

The advantage of the desmo valve train is reduced horsepower loss as compared to the efforts required to open the valves against heavy valve springs.

As discussed earlier, that is just ONE of the advantages.....

Anyone want to put a number as to how much hp is thusly gained. ?
In a desmo 125cc, which is where Duc started, it ain't gunna be much.
So there must be other advantages !!

Are the loss's opening valves ,regained when they close,after all springs store energy.? carn't be one way.

fredful said:

The advantage of the desmo valve train is reduced horsepower loss as compared to the efforts required to open the valves against heavy valve springs.

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Rohan said:

Anyone want to put a number as to how much hp is thusly gained. ?

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Power consumption on a valvetrain is roughly in the 2-5kW region. The desmo is better but not by much as it basically comes down to friction. Desmos have two friction points with relatively low friction losses where std valves have only one contact but with relatively high friction loss. Desmos also have higher inertia.


Tim

This statement of valve spring loss, is not correct . for every action there is an equal re-action . If a valve requires 100 lb to compress it,the spring acts in the opposite direction with 100lb.. ? If this was not true then i need the figures.

Tintin said:

Rohan said:

Anyone want to put a number as to how much hp is thusly gained. ?

Click to expand...

Power consumption on a valvetrain is roughly in the 2-5kW region. The desmo is better but not by much as it basically comes down to friction. Desmos have two friction points with relatively low friction losses where std valves have only one contact but with relatively high friction loss. Desmos also have higher inertia.


Tim

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john robert bould said:

This statement of valve spring loss, is not correct . for every action there is an equal re-action . If a valve requires 100 lb to compress it,the spring acts in the opposite direction with 100lb.. ? If this was not true then i need the figures.

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This may be true at near zero rpm (minus friction losses) but as rpm increases, recovery of work/energy (minus friction losses) to open a valve against the valve spring force and inertia goes to zero as the system approaches valve float. That is, when the valve mechanism in a conventional sprung valve floats, it got nothing to give back to the back side of the cam lobe to recover energy/work. So go figure.

Desmo is about high-rpm valve control. It was invented long before exotic spring alloys and pneumatics. Ducati has stuck with it and developed it to a high degree, but it's still old, outdated tech. We're all familiar with that stuff.

john robert bould said:

This statement of valve spring loss, is not correct .

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It is called friction loss. Not valve spring loss. And it is correct. It has nothing to do with storing potential energy in a spring.

I try to explain it once again: The valve spring sets the whole valve train under pressure as soon as valve play is overcome. This results in normal forces in all contact points within the system - e.g. in the cam-to-follower contact, whatever this may look like. This normal force is somehow reflected in the torque needed to turn the camshaft - as are the friction forces in the bearings. Friction is lost, gone, perdu, hasta la vista.

Obviously there are no springs in a Desmo so the normal forces at the two contact points for each of the two cams are potentially lower - but there's two. And there's roller follers one benefit of which is the reduction of friction losses. So it highly depends on the individual system and cannot really be generalised. I know the numbers for the Toyota F1 desmo and the std layout but please forgive me that I won't tell them publically....



Tim

Tintin said:

Obviously there are no springs in a Desmo

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This is not strictly accurate.
Most early-ish Ducati desmos have a light set of valve springs fitted.

Dunno about the recent ones.
Duc found early on that it could be quite difficult to start a purely desmo - single cylinder, cause thats where Ducs started with them.
Without this, the valves didn 't always seat 100%, and with the valve open even a mere trace they wouldn't start.
A light set of springs solved this, instantly.

I rather think the Merc GP cars may have had this too...

I understood that a large part of the value of the desmo valve system was that with a big rev, from too large a handful of throttle,
the valves wouldn't clash, so the engine survived to continue to do battle. As someone said, "valve control".
The value of this, in a race bike, cannot be over-estimated....

Actually, the production Ducati Desmo 250, 350 and 450 singles came standard with quite strong hairpin valve springs. On mine, I can just press them down with my fingers to release the spring retainer. The closing rockers can be modified to take much lighter 'helper' springs as fitted to the V twins from the 70s to the 90s and onwards. This is what I have done (with thanks to forum member GRM 450). A long time ago, I ran the motor without any springs and it could be started. If the closing rocker clearances are too large, then it might be tricky to start. Once started, gas pressure slaps the valves back fully onto their seats.

My experience of desmos is that the valve clearances in the old 70s engines need very frequent adjustment, and because of cam grinding inaccuracies, it is better to remove the heads to set the clearances to avoid rocker/cam binding. It is a lot of bother for very little if any practical return. The top Ducati tuners have proved that the valve spring engines are just as effective as the desmos and much less hassle. The modern desmo Ducatis are built to much closer tolerances and from better materials, resulting in much longer service intervals without having to remove the heads to set the valve clearances. They too have light 'helper' return springs. The engine efficiency arguments mentioned above are interesting, but equally, Ducati use their desmo system as a marketing tool to very good effect because they are still the only production machines using the system, so it has given them an aura of exotic mystique.

The desmo system had another advantage back in the day, when brakes were poor and the revs would soar on the overrun using engine braking, there was no risk of valve tangling.

Ohv pushrod owners, consider yourselves lucky you don't have to maintain a desmo Ducati. It's a real luxury to be able to whip off the valve covers, slacken the lock nut and turn the adjuster against the feeler gauge. Job done, and then you are back on the road again, which is what it is all about.

daveh said:

Ohv pushrod owners, consider yourselves lucky you don't have to maintain a desmo Ducati. It's a real luxury to be able to whip off the valve covers, slacken the lock nut and turn the adjuster against the feeler gauge. Job done, and then you are back on the road again, which is what it is all about.

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Yes... and to not have to take the heads off the bike to do it...
And in the case of the early 8 valvers, the engine out of the frame. Really. :roll:

Rohan said:

Tintin said:

Obviously there are no springs in a Desmo

Click to expand...

This is not strictly accurate.
Most early-ish Ducati desmos have a light set of valve springs fitted.

Click to expand...

Sure, but the spring rate of these helper springs is a fraction of that of a valve spring and only there to take out the little bit of play you'd need to overcome tolerance build up. So let me modify that slightly: The springs forces in a conventional Desmo setup can be neglected (and there are desmos without helper springs .... )


Tim

Tintin said:

So let me modify that slightly: The springs forces in a conventional Desmo setup can be neglected

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The helper springs may be 'light', but they are not that light.... ?

Rohan said:

Tintin said:

So let me modify that slightly: The springs forces in a conventional Desmo setup can be neglected

Click to expand...

The helper springs may be 'light', but they are not that light.... ?

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On balance I'd be inclined to agree with Tintin - they offer very little resistance, and for mathematical purposes I'd disregard them.
I seem to recall the 851 springs being a tad stronger than the bevel ones, but still easy enough to rotate the cam by hand.
Otherwise we'd be getting into discussing the merits of Thackeray washers vs. accurate shimming of the rockers (as per Ducati practice) as well...