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steamcar-template.qxp 15/11/2005 22:28 Page 36 (f) This can be admirably demonstrated when attempting to drive a steam car that uses a single mushroom variant of an inlet valve for the throttle (regulator). Considerable force is required to open the valve, usually fully. Any attempt to throttle back lets the valve take over shutting itself in an instant. A definite use of kangaroo juice. Can We "Get it Right"? Possibly, with 11 Advantages against 5 Disadvantages, according to the Duke of Wellington's theory, we carry on. Let's deal with each of the Disadvantages. Bash Valves - have proven that they can do it using "hammer blow" principle without detriment. AT cut- offs 30, 25, and 20% the lead produced by piston open the valve is tolerable. At 17% or less it becomes a positive advantage. Cam assistance is necessary until 3% then leave it to the Bash mechanism. The Achievable Desmodromic Valve Gear (see accompanying drawing) used very successfully for the past 40 years on racing Ducatis. Basically two additional cams to close the valve. The 500 c.c. Norton desmodromic engine. This valve gear (left), tried experimentally in 1959, used two shafts for each valve. The “closing” rockers are forked and bear on collars. In the Ducati desmodromic valve-gear sysem the central shaft carrying the “closing” cams is bevel-driven from a vertical drive-shaft. Comment Complicated (particularly on three dimensional cams) high rates of friction on HP steam engines. Lotus Active Valve Train (or Similar) (see Web page www.lotuseng.com) a hydro/electronic fully programmable with valve gear or cams. Comment Very interesting, on paper looks as though it can do anything asked of it right up to 4,000 rpm. Is the added complexity worth pursuing? Double Beat or Balanced Poppet Valve (see accompanying drawing) More in PART 2. I will leave the last word to Bugatti "This arrangement of two heads (double beat) is indispensable in the case of a steam engine, to compensate for the action of the pressure prevailing in the admission manifold which tends to open the valve". Doug Leeming The Steam Car Page 36.

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Desmodromics Mick Walker Explains How Ducati Beat Tbe World with Spring-Less Valve Operation
og , Desmodromics Mick Walker explains how Ducati beat tbe world with spring-less valve operation HE WORD desmodmmic wil! not be the bounce and get a higher-revving engine successful and was not developed, but in found in the Oxford or any other - in theory. the 1920s several other manufacturers tried T English dictionaries. It was coined This had been known since the early days variants of it. One layout, the Vagova, from two Greek words, meaning 'controlled of the internal combustion engine but for utilized a cam track embodying inner and run' and its mechanical function is to elimi- many years no designer managed to success- outer cam forms which guided a roller nate one of the phenomenon of valve float, fully harness it. One of the first examples of attached to one end of a 'rocker', the other or 'bounce'. This happens at high revs when completely positive mechanical valve oper- end of the rocker was forked to embrace the valve springs are unable to respond ation was used by the French Delage concern the valve stem. To provide the required quickly enough to close the valve back on in its grand prix car of 1914 - and the freedom for seating, the pivot of the rocker their seats. 11le desmodromic idea was to French knew the method as desmod- was given a small amount of spring-Ioaded replace troublesome springs with a romique. float parallel to the valve axis. me(\. jcal closing system much like that The Delage engine employed four valves Alternative methods investigated were to usedló open them.
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