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From: rs55611@ihuxk.UUCP (Robert E. Schleicher)
Newsgroups: net.auto
Subject: Re: Camless valve operation
Message-ID: <858@ihuxk.UUCP>
Date: Fri, 18-Jan-85 14:13:32 EST
Article-I.D.: ihuxk.858
Posted: Fri Jan 18 14:13:32 1985
Date-Received: Sat, 19-Jan-85 01:30:34 EST
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Organization: AT&T Bell Labs, Naperville, IL
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For people who've been wondering what the term "desmodromic" (sp?)
means, it's a term that's been used in Road and Track articles
(in particular, one describing the engine used in 1930's Mercedes-Benz
Grand Prix cars) in which there are no valve springs to return the valves
to a closed position.  Instead, some form of positive return action is used.
In one variant, a separate cam lobe is used to close the valve.  This implies
two cam lobes per valve, perhaps on separate shafts.  In another theoretically
possible variant, the cam lobe has a slot in it through which the end of the
valve stem "travels" as the cam shaft rotates.  Thus, the valve is both "pushed"
and "pulled" by the cam lobe, rather than being pushed by the cam lobe and
pushed back by a spring.  

In theory, desmodromic valve operation should allow higher RPM operation 
without valve float, although there is a complexity penalty.

Bob Schleicher
ihuxk!rs55611