Talk:Desmodromic valve

animation

That image is not an accurate depiction of desmodromics. There is no positive closing action with one cam lobe. There should be a second cam lobe with a complementary profile to close the valve.Seasalt 15:15, 23 September 2006 (UTC)[reply]

Better clean my glasses. Could see it tonight.I was wrong, but the second cam is hard to c 4 me..Seasalt 12:16, 24 September 2006 (UTC)[reply]

The cams are there, but the animation is incorrectly done, as the closing cam doesn't actively close the valve...

It looks to me like the cam knocks it closed and then the pressure differential holds it closed. It makes sense. You just need the valve closed long enough for the pressure differential to build up. --Gbleem 15:17, 22 April 2007 (UTC)[reply]

"How it works" section

Is not a description of how it works but the Ducati patent on a way of changing the shims by sliding the opening rocker to one side.

"Advantages/Disadvantages" section

These sections make very specific statements and claims which should backed up by citations (i.e. "high speed photography work..." etc)

Otherise, it gets removed. Thanks. Izaakb 20:28, 21 January 2007 (UTC)[reply]

The Advantage/Disadvantage sections is turning into a discussion of springs, this article is just a discussion of desmodromic valves. I am thinking these sections are not useful, they certainly should not be 60% of the text. Maybe restricted down to one paragraph each at the most. Izaakb 03:53, 22 January 2007 (UTC)[reply]

Desmodromic valves are used so rarely that very little research has been done into them. Indeed Ducati are the only company to have any success with them, and hence it is really only their technical department that has done any work on the system. Hence citations are hard to come by. What the article says is entirely correct. The proposed deletion would only remove another of the few sources of information on desmo systems. (Izaakb, i would have thought that as a motorcycle historian you would appreciate this!) Inginero990 00:28, 25 January 2007 (UTC)[reply]

My opinion of the information is irrelevant -- Wikipedia requires that the claims or information be verifiable and cited. If citations are "hard to come by" then the work is not verifiable and thus, cannot be posted on Wikipedia. If you need an explanation of this policy, please refer to this Wikipedia:Verifiability. In short:

==
1. Articles should contain only material that has been published by reliable sources.

2. Editors adding new material should cite a reliable source, or it may be challenged or removed by any editor.

3. The obligation to provide a reliable source lies with the editors wishing to include the material, not with those seeking to remove it.
==

Izaakb 04:09, 25 January 2007 (UTC)[reply]

Removed uncited sections

I removed the two uncited "Advantages/Disadvantages" section. Editor Jobstbrandt has not offered to post citations to the work he has referred to which is counter to Wikipedia policy (i.e. Wikipedia:Verifiability and Wikipedia:No original research).

I've communicated with the editor several times asking him to post citations, but he has refused.

And just to make it clear to everyone, I have no problem with the content of the sections (except perhaps the "mental blindness" comment) save for the fact that the information is uncited opinion. Izaakb 22:17, 25 January 2007 (UTC)[reply]

Disadvantages

I see that much of the editing I did was not noticed. The "mental blindness" referece was removed early on and citations were added as I could find them on the web, much of the subject not being common knowledge. I would like to resubmit the article under a new title such as "Desmodromic drive, then and now" or something similar. It is, after all, the technical competition conventional cam, flat tappet, and spring return valve drive against which desmodromic valve drive is measured.

Jobst 20:56, 27 January 2007 (UTC)[reply]

Why?

Why would an engine maker bother with a desmodromic system? What are the disadvantages of springs? Is there an appreciable lag in closing time when a spring is used? What problem was the desmodromic system designed to solve?

Well it solves the problem of choosing springs because you would want springs that are light enough that they do not create huge amounts of drag at low rpm but stiff enough that it closes the valves at high rpm. when going into the high revs like bikes do, sometimes vlaves don't close fast enough and that robs power and then the piston can hit the open valve and just blow up the engine. thats basically what desmo valves solves. Finbar Canavan 03:49, 15 May 2007 (UTC)[reply]

A spring valve requires more work by the engine to open the valve than a desmo valve. A desmo "helper" spring has about 7-8 lbs of pressure whereas a traditional spring poppet valve may have over 100 lbs of sprung tension. Consider that with a 100 lb spring, the cam shaft, when turning, must overcome 100 lbs of tension per spring (a 2 valve engine will have two springs per cylinder). That robs HP from the engine, since the cam shaft is turned by engine work.

A desmo valve head has no more than 7-8 lbs tension per valve, so the camshafts are practically turning freely, which does not rob HP from the engine. IzaakB (my Talk)contribs 15:36, 15 May 2007 (UTC)[reply]

Okay, that makes sense. Is the drag from the spring significant enough to merit this, though? I suppose it must be. Also, wouldn't the spring put all the energy it absorbed back into the camshaft as it extended again? Slight losses from friction, obviously. Aside from that, everything makes sense. A stiffer spring would be needed to close the valve quickly, but is undesirable due to 'robbing' HP from the engine. Has this been documented somewhere, with statistics? That kind of data would make a great addition to this page, if available. Phasmatisnox 03:42, 16 May 2007 (UTC)[reply]

I don't know where it has been documented, I am sure Ducati has some data on it. The best way for you to see how spring pressure affects the cam is to take a head and turn the cam by hand. Cam lobe profiles often do not permit the spring to "put back" the energy into the camshaft because the lobe shape dictates the timing of the valve opening and closing, thus, the lobe is always working against the spring tension. If you have a desmo head, you only have spring tension (and only about 7-8 lbs of it) when you turn the lobe into the opening rocker, when the closing rocker begins to move, there is no tension whatsoever, just the weight of the valve! Conversely, the 100 lb spring is always pressing against the cam lobe, first it is working against the opening lobe and second it is pressing against the turning lobe, but it cannot "speed up" the engine or add back HP, it is just riding the curvature of the cam lobe.

I wish I had some data on this. I am sure someone has it. I read somethings done at University of Bologna (where else?) on the topic, but none were published. IzaakB (my Talk)contribs 04:11, 16 May 2007 (UTC)[reply]