Editing Sleeve valve (section)

===Disadvantages===
A number of disadvantages plagued the single sleeve valve:

* Perfect, even very good, sealing is difficult to achieve. In a poppet valve engine, the piston possesses [[piston ring]]s (at least three and sometimes as many as eight) which form a seal with the cylinder bore. During the "breaking in" period (known as "running-in" in the UK) any imperfections in one are scraped into the other, resulting in a good fit. This type of "breaking in" is not possible on a sleeve-valve engine, however, because the piston and sleeve move in different directions and in some systems even rotate in relation to one another. Unlike a traditional design, the imperfections in the piston do not always line up with the same point on the sleeve. In the 1940s this was not a major concern because the poppet valve stems of the time typically leaked appreciably more than they do today, so that oil consumption was significant in either case. To one of the 1922–1928 Argyll single sleeve valve engines, the 12, a four-cylinder 91 cu. in. (1,491 cc) unit, was attributed an oil consumption of one gallon for 1,945 miles,<ref>W. A. Frederick, SAE Journal, May 1927</ref> and 1,000 miles per gallon of oil in the 15/30 four-cylinder 159 cu. in. (2,610 cc).<ref>George A. Oliver, ''The Single Sleeve-Valve Argylls'', Profile Publications Number 67 - Cars -, London 1967</ref> Some proposed adding a ring in the base of the sleeve, between sleeve and cylinder wall, or a Dykes ring on the 'Junk Head'. Single-sleeve-valve engines had a reputation of being much less smoky than the Daimler with engines of Knight double-sleeve engines counterparts.
* The high oil consumption problem associated with the Knight double sleeve valve was fixed with the Burt-McCollum single sleeve valve, as perfectioned by Bristol. The models that had the complex '[[junk head]]' installed a non-return purging valve on it; as liquids cannot be compressed, the presence of oil in the head space would result in problems.  At [[Dead centre (engineering)|top dead centre]] (TDC), the single-sleeve valve rotates in relation to the piston. This prevents boundary lubrication problems, as piston ring ridge wear at TDC and bottom dead centre (BDC) does not occur. The Bristol Hercules time between overhauls (TBO) life was rated at 3,000 hours, very good for an aircraft engine, but not so for automotive engines.<ref>LJK Setright, ''Some Unusual Engines'', London, 1979, p 62</ref> Sleeve wear was located primarily in the upper part, inside the 'junk head'. Hewland and Logan claimed solving the Oil consumption in their single sleeve valve, single cylinder, 500 cc prototype engine, by adding a ring in the sleeve base and a Dykes ring on Junk Head.
* An inherent disadvantage is that the piston in its course partially obscures the ports, thus making it difficult for gases to flow during the crucial overlap between the intake and exhaust valve timing usual in modern engines.  The 1954 printing of the book by Harry Ricardo ''The High-Speed Internal Combustion Engine'', and also some patents on sleeve valve production, point out that the available zone for ports in the sleeve depends on the type of sleeve drive and bore/stroke ratio; Ricardo tested successfully the 'open sleeve' concept in some two-stroke, compression ignition engines. It not only eliminated the head rings, but also allowed a reduction in height of the engine and head, thus reducing frontal area in an aircraft engine, the whole circumference of the sleeve being available for exhaust port area, and the sleeve acting in phase with the piston forming an annular piston with an area around 10% of that of the piston, that contributed to some 3% of power output through the sleeve driving mechanism to the crankshaft. The German-born engineer [[Max Bentele]], after studying a British sleeve valve aero engine (probably a [[Bristol Hercules|Hercules]]), complained that the arrangement required more than 100 gearwheels for the engine, too many for his taste.<ref name="Bentele, 100 gears" >{{cite book
  |last=Bentele  |first=Max  |author-link=Max Bentele
  |year=1991
  |title=Engine Revolutions: The Autobiography of Max Bentele
  |location=Warrendale, Pennsylvania  |publisher=[[Society of Automotive Engineers|SAE]]
  |isbn=978-1-56091-081-7
  |ref=Bentele, Engine Revolutions
  |pages=5
  |quote=During World War II, my original enthusiasm for the sleeve-valve engine simplicity proved to be based on dubious premises. My inspection of a captured Bristol two-row [[radial engine]] revealed a bucket full of gear wheels for the sleeve drive. I believe there were over 100 gears!
}}</ref>
* A serious issue with large single-sleeve aero-engines is that their maximum reliable rotational speed is limited to about 3,000 RPM, but the Mike Hewland car engine was raced above 10,000 rpm without toil.
* Improved fuel octane, above about 87 RON, have assisted poppet-valve engines’ power output more than to the single-sleeve engines’.{{citation needed|date=May 2013}}
* The increased difficulty with oil consumption and cylinder-assembly lubrication was reported as never having been solved in series-produced engines. Railroad and other large single sleeve-valve engines emit more smoke when starting; as the engine reaches operating temperature and tolerances enter the adequate range, smoke is greatly reduced. For two-stroke engines, a three-way catalyst with air injection in the middle was proposed as best solution in a SAE Journal article around the year 2000.
* Some (Wifredo Ricart, Alfa-Romeo) feared the build-up of heat inside the cylinder, however Ricardo proved that if only a thin oil film is retained and working clearance between the sleeve and the cylinder was kept small, moving sleeves are almost transparent to heat, actually transporting heat from upper to lower parts of the system.
* If stored horizontally, sleeves tend to become oval, producing several types of mechanical problems. To avoid this, special cabinets were developed to store sleeves vertically.
* Equivalent implementations of modern variable valve timing and variable lift are impossible due to the fixed sizes of the port holes and essentially fixed rotational speed of the sleeves. It may be theoretically possible to alter the rotational speed through gearing that is not linearly related to the engine speed, however it seems this would be impractically complex even compared to the complexities of modern valve control systems.