Encyclopedia Hoonatica: Non-Traditional Valve Systems

 
How about a little Encyclopedia Hoonatica to make your hump day a little less humpy? It’s funny how one thing leads to another, and from where inspiration arises. A couple of days ago I was listening to the radio, and a story came on about a man who needed a new heart valve. Once the stuff of science fiction, prosthetic cardiac valves are now commonplace, and thousands of people go about their daily lives with one ka-thumping in their chests. All that amazing medical advancement got me to thinking about the valves that are almost as important as the ones in Cupid’s target, meaning the valves that allow the traditional ICE to work. But what if that engine, wasn’t so traditional?
The original poppet valve predates the internal combustion engine, having been used in steam engines and pumps for years prior – and in fact the Presta or Schrader valves on your tires are examples of them. The earliest forms of reciprocating ICEs were just as likely to have slide valves, but as compression ratios and engine speeds increased, the simplicity and effective nature of the coil-sprung poppet became a standard form of gas flow management in vehicle applications. F-heads, L-heads, and OHV engines, there have been plenty of  applications of that traditional poppet with coil spring over the years, and of course the form remains the standard fitment to this day in most of the cars, trucks and motorcycles on the road.
Except for those which don’t. Today, we’re cataloging the automotive, motorcycle and hell, even snowmobile, engines that eschew that traditional application of the coil on mushroom valve system for something a little more, shall we say, esoteric? I’ll start off with one that we all know – an easy one to get the juices flowing as it were – the desmodromic valve system. This mechanism utilizes mechanical opening and closing of the valve – so as to provide precise valve timing (before computer engine controls) and limit valve float – the condition when engine speed causes the valve’s ineria to overcome the spring’s ability to push it closed. Mercedes applied desmo heads to its 1954-55 W196 Formula One cars, and Italian motorcycle maker, Ducati has made it a feature of their wide-angle twins for more than 5 decades. The downsides of the Desmo system are additional frictional losses, weight, and maintenance- the last being either a frustration or a badge of honor among Duck owners.
There are other less-common valve systems in use today, and a lot that have come and gone – there have been other methods of valve return employed, including torsion bar and leaf spring, and of course there are a number of engines that shun the poppet altogether, and I’m sure we’ll see some examples of those here too. So, what say we get this party jump started, how many non-traditional valve system engines can you name?
Don’t forget the rules: Read the existing posts first, don’t post duplicates, and shrink your large photos to 500 pixels wide.
Image sources: [ducatimonster, two-stroke-engine.com]