Editing Sleeve valve (section)

== Modern usage ==
The sleeve valve has begun to make something of a comeback, thanks to modern materials, dramatically better [[Machining|engineering tolerances]] and modern construction techniques, which produce a sleeve valve that leaks very little oil. However, most advanced engine research is concentrated on improving other types of internal combustion engine designs, such as the [[Wankel engine|Wankel]].

[[Mike Hewland]] with his assistant John Logan, and also independently [[Keith Duckworth]], experimented with a single-cylinder sleeve-valve test engine when looking at [[Cosworth DFV]] replacements. Hewland claimed to have obtained {{convert|72|hp|abbr=on}} from a 500&nbsp;cc single-cylinder engine, with a [[Brake specific fuel consumption|specific fuel consumption]] of 177–205&nbsp;g/HP/hr (0.39–0.45&nbsp;lb/HP/hr), the engine being able to work on [[creosote]], and with no specific lubrication supply for the sleeve; they said having solved the oil consumption issue by adding a Dykes ring on 'Junk Head'.

[[File:RCV 120SP sleeve valve model engine.jpg|thumb|right|An RCV "SP" series 20 cm3 (1.20 cu. in.) displacement sleeve valve model engine]]

An unusual form of four-stroke [[model engine]] that uses what is essentially a sleeve-valve format, is the British RCV series of "SP" model engines, which use a rotating cylinder liner driven through a bevel gear at the cylinder liner's "bottom", which is actually at the aft end of the cylinder; and, even more unusually, have the propeller shaft—as an integrally machined part of the rotating cylinder liner—emerging from what would normally be the [[cylinder head]], which in this design is placed at the extreme front of the engine, achieving a 2:1 gear reduction ratio compared to the vertically oriented crankshaft's rotational speed. The same firm's "CD" series of model engines use a conventional upright single cylinder with the crankshaft used to spin the propeller directly and also use the rotating cylinder valve.  As a parallel with the earlier Charles Knight-designed sleeve-valved automotive powerplants, any RCV sleeve-valved model engine that is run on model [[glow engine]] fuel using [[castor oil]] (about 2% to 4% content) of the maximum 15%-content lubricant in the fuel allows the "varnish" created through engine operation to provide a better pneumatic seal between the rotating cylinder valve and the unitized engine cylinder/head castings, initially formed while the engine is being broken in.<ref>{{cite web|url=http://www.rcvengines.com/pdf_files/saepaper.pdf |title=The Rotating Cylinder Valve 4-stroke Engine (SAE Paper 2002-32-1828) |author=Keith Lawes |access-date=2012-01-03 |url-status=dead|archive-url=https://web.archive.org/web/20111112180807/http://www.rcvengines.com/pdf_files/saepaper.pdf |archive-date=November 12, 2011 }}</ref>

Another concept, the Rotating Liner Engine, has been developed, where the wear and friction benefit of the sleeve valve is exploited in a conventional engine layout.  A friction reduction of the order of 40% has been reported for a heavy duty diesel.{{citation needed|date=July 2022}}

The same company can also supply somewhat larger engines for use in military drones, portable generators and equipment such as lawn mowers.<ref>{{cite web |url=http://www.rcvengines.com/applications_uav.html |title=RCV Engines Web Site |access-date=2018-11-25 |archive-date=2018-11-26 |archive-url=https://web.archive.org/web/20181126132118/http://www.rcvengines.com/applications_uav.html |url-status=dead }}</ref>