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Let's Talk Cyclecars

Discussion in 'The Hokey Ass Message Board' started by Bigcheese327, Dec 4, 2007.

  1. Yes, the radius rods locate the axle in place and prevent wind-up when braking.
     
  2. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    And here's the reason for it ... pulled from the web, but seems to make sense.
    "The Mercedes application had two radius rods running forward to the frame rails, and a rotating joint in the middle of the De Dion tube to prevent the tube from acting as a massive tubular anti-roll bar."

    I have an idea that if the radius rods met at a common point the articulation would not be required. I'm guessing this is all about roll centre and stuff that I'm nowhere near qualified to speak on.
     
  3. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,954

    Ned Ludd
    Member

    That is true. It's mainly about packaging and geometry, though: there probably isn't space for the radius arms to meet where they ought, and a four-bar is geometrically correct in roll only in relation to one position in the vertical travel range. The same sort of geometric absoluteness is seen in the lateral-locating device, a channel attached to the rearend housing, in which a pin attached to the axle tube slides; also in the way the DeDion assembly is in the horizontal plane of the rear wheel axis, rather than "dropped" as on a '70s Alfetta. The car seems to be a didactic essay on suspension geometry - which I suspect does not come across quite as well in any language as German :)
     
  4. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    In another forum I subscribe to I delved into the mechanism used to generate the "push-pull" valve actuation on the Le Rhone rotaries. They used a single rod to open both the inlet & exhaust (admission/echappement).
    What's this got to do with cyclecars? The Salmson AL's from the early 20's also used a single push-pull rod system: does anyone out there know how it was done on these motors? - even better if you can post an image of it ... 'twould be better than the proverbial thousand words;)
    ps: if you've never viewed "Monsieur Hulot's Holiday" (les Vacances de M. Hulot) then you should.
     

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  5. It's in my DVD collection... :D
     
  6. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    Found a web site en français which refers to the Salmson AL soupapes as being "semi-desmodromique" (Ducatisti, eat your heart out ... this is from 1921!).
    However, my hoping for an image or diagram of the mechanism is justified when the Google translation of it comes up as "...The cams are supplemented against the cam which actuates the pushers cylindrical inverted by recalling, such that the valve springs are only to close them. Thus, a high-speed closure and eliminates the risk of bounce or panic valves, often at a time when the metal springs is not very efficient.":eek:
     
  7. noboD
    Joined: Jan 29, 2004
    Posts: 7,093

    noboD
    Member

    Onelung, the picture is not very clear.
     
  8. noboD
    Joined: Jan 29, 2004
    Posts: 7,093

    noboD
    Member

    Found this from 1910. The part that confuses me, Onelung, is the valve springs in your statement. I thought Desmos didn't have springs.
     

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  9. chuxx
    Joined: Jul 15, 2007
    Posts: 208

    chuxx
    Member

    Here's a couple of pics of my attempt at a quarter eliptical front suspension. This IS my first rodeo so I'm wide open to advice and direction. I'm not trying to build a track car or cross country cruiser, just a fun little cyclecar to tool around town in. ImageUploadedByTJJ1357618383.082655.jpg
    ImageUploadedByTJJ1357618445.050690.jpg


    Posted from the TJJ App for iPhone & iPad
     
  10. chrisp
    Joined: Jan 27, 2007
    Posts: 812

    chrisp
    Member

    You should check this eventhough it's in french:
    http://tricyclecaristes.forumr.net/t60-gn-cyclecar
    Bunch of cool period pictures plus some detailed pictures.
    On the page 4 their is a detailed description of how the engine architecture and how it works: The exhaust valve sits bellow the intake valve: it's the key to the single cam that actuates both valves. The intake has an "hairpin" style spring (same as airplane it says) and the cam that actuate the intake valve is the cam that actuate the exhaust one but without spring thus a semi desmo engine.

    Still on that page 4 that 4 cyl GN is absolutely gorgeous.
    http://i82.servimg.com/u/f82/12/92/44/08/gn10.jpg

    http://i82.servimg.com/u/f82/12/92/44/08/gn_210.jpg
     
  11. UKAde
    Joined: Nov 13, 2002
    Posts: 502

    UKAde
    Member
    from Oxford UK

    Often desmo systems have light springs to seal the valves for starting purposes as once the engine is running the compression does that job
     
  12. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    My post, #3638, is a direct Google translation and it refers, as you can see to a "semi desmodromique" system. Whatever that means.
    And no, it is not clear...not at all clear.:(
     
  13. charlesf
    Joined: Jan 14, 2009
    Posts: 156

    charlesf
    Member

    Charlie,
    You and I are on the same track. I'll try to get a photo up so you can see mine.

    Chuck
     
  14. charlesf
    Joined: Jan 14, 2009
    Posts: 156

    charlesf
    Member

    Charlie,
    You and I are on the same track. I'll try to get a photo up so you can see mine.

    Chuck
     
  15. charlesf
    Joined: Jan 14, 2009
    Posts: 156

    charlesf
    Member

    Here is my quarter eliptic set up.
     

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  16. chuxx
    Joined: Jul 15, 2007
    Posts: 208

    chuxx
    Member

    Looks good, Chuck. That's about where I plan to mount my friction shocks too.
     
    Last edited: Jan 8, 2013
  17. noboD
    Joined: Jan 29, 2004
    Posts: 7,093

    noboD
    Member

    I've never had the chance to work on a Desmo, but think I understand the theory. I saw pics with the light springs, but don't consider them to be real valve springs as UKAde describes. Maybe T-Head or someone else can explain what semi-desmodromic means. It sounds like being semi pregnant.
     
  18. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    I think it means they have helper springs...but don't quote me on that. ;)
     
  19. chrisp
    Joined: Jan 27, 2007
    Posts: 812

    chrisp
    Member

    The intake pushrod has provision to actuate the cam for the exhaust.
    What I said is wrong or nobody read or understood it??
     
  20. banjeaux bob
    Joined: Aug 31, 2008
    Posts: 5,848

    banjeaux bob
    Member
    from alaska

    Image courtesy of G.L...
     

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  21. ebtm3
    Joined: May 23, 2007
    Posts: 837

    ebtm3
    Member

    See-

    http://ucapusa.com/lost_marques_salmson.htm

    Read down to the seventh paragraph--it tells how the valve gear worked. This system must have been like the Stoddard-Dayton. Overhead valves, set slightly spayed (as in a hemispherical chamber--although not sure that either the Salmson or S-D was truly a hemi --either, or both may have been a pent roof chamber. A long rocker arm, pivoted over the center of the bore, comes close to a valve stem tip at either of it's ends. Push rod attaches to one end of rocker. Exhaust valve has heavy spring, Intake light spring. Pushrod has a heavy spring at its base. Cam pushes pushrod up, compressing PR base spring and exhaust valve spring and ex. valve opens. Exhaust valve closes when PR goes down to a "neutral" position, where neither valve is open. After a dwell period, the lifter drops down into a dip in the cam, and the heavy PR spring overcomes the light intake valve spring and intake opens. Appropriate period later, lifter and PR go back up to "neutral" for compression and firing stroke.

    Now what the hell is desmodronic --semi or otherwise-- about this would take some Frenchman to come up with. Wouldn't be the first--or last time a manufacture lied about their product.

    One interesting about the arrangement is that absolutely no valve overlap is possible.

    Herb
     
  22. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    Thanks Herb ... that just about makes it clear for me - although why there seems to be no image or diagram of it out there in cyberspace is frustrating.
    And yes ... I quite agree with your comment on its being called "semi - desmodromique". We had a Chrysler product here in Australia which they called a "hemi". It was more like a semi-hemi, which is what the more cynical motor heads called it.
     
  23. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    The print size is too small for me to cope with: sorry.:eek:
    There's more here on "semi desmos", with reference to the Salmson 8 cylinder racing engine, which is a world away from the AL cyclecar.
    http://members.chello.nl/~wgj.jansen/text/sefac.html
    Edit: here's the GN motor, but my reading of this is that it still has two pushrods?
     

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  24. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,954

    Ned Ludd
    Member

    Someone - who escapes me - investigated a curious concentric-valve arrangement during the Edwardian era, to what end I cannot imagine.

    Using one cam lobe to activate more than one valve is common enough, though. Everyone familiar with air-cooled VWs will know that there are only four lobes on the camshaft, as opposite valve events occur 180° of cam rotation apart. Less well known is the way one set of lobes was used to activate intake and exhaust valves in the 16-valve Triumph Dolomite Sprint engine of the '70s:
    [​IMG]
     
  25. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    I'm imagining that would place the ultimate restraint on inlet/exhaust timing relative to each other since they are employing the same cam profile?
    The other thought is that like the XK 6 cylinder engines, valve clearance is done by fitting shims. Wonderful...:rolleyes:
     

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  26. UKAde
    Joined: Nov 13, 2002
    Posts: 502

    UKAde
    Member
    from Oxford UK

    Despite the cam lobe being the same For the inlet and exhaust the exhaust lift and acceleration is dependent on the rocker ratio and the follower radius whereas the inlet can only be 1 to 1

    Also in that drawing both valves should be off their seats as neither follower is on the base circle of the cam yet
     
    Last edited: Jan 10, 2013
  27. onelung
    Joined: Feb 19, 2010
    Posts: 181

    onelung
    Member
    from Adelaide

    What I might have been trying to say/should have said was that the dwell would be the same for exhaust as well as inlet... thanks for pointing out that the lift of the exhaust depends on the rocker ratio;)
    Is/was valve overlap possible with this arrangement?
     
  28. Huvius
    Joined: Oct 6, 2012
    Posts: 32

    Huvius
    Member
    from Colorado

    I am thinking that the cam/inlet rocker/exhaust design was also used on Bristol engines which IIRC were more or less a prewar BMW design.
    Alfa Romeo also used it on their V6 engines. I had an Alfa 164 which had that valve actuation arrangement.
     
  29. Huvius
    Joined: Oct 6, 2012
    Posts: 32

    Huvius
    Member
    from Colorado

    I am thinking that the cam/inlet rocker/exhaust design was also used on Bristol engines which IIRC were more or less a prewar BMW design.
    Alfa Romeo also used it on their V6 engines. I had an Alfa 164 which had that valve actuation arrangement.
     
  30. UKAde
    Joined: Nov 13, 2002
    Posts: 502

    UKAde
    Member
    from Oxford UK

    The dwell is different on the inlet and exhaust as the exhaust has a curved follower which I think it means it has more dwell

    And the aver lap occurs because the of the orientation of both followers if you look at the drawing if the cam turns clockwise the inlet follower is on the flank of the cam so is starting to open whereas the exhaust follower is on the closing flank so is nearly closed but as I said before the drawing should how both valves partly open
     

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