Overhead valve

An overhead valve engine (OHV engine), or pushrod engine, is a reciprocating piston engine whose poppet valves are situated in the cylinder head. An OHV engine's valvetrain operates its valves via a camshaft within the cylinder block, cam followers (or 'tappets'), pushrods, and rocker arms. An overhead valve engine (OHV engine), or pushrod engine, is a reciprocating piston engine whose poppet valves are situated in the cylinder head. An OHV engine's valvetrain operates its valves via a camshaft within the cylinder block, cam followers (or 'tappets'), pushrods, and rocker arms. The OHV engine was an advance over the older flathead engine, whose valves were situated in the cylinder block. Some early 'OHV' engines known as 'F-heads' used both side-valves and overhead valves. A variation over the OHV design is the overhead camshaft, or 'OHC', engine, whose camshaft lies in the cylinder head itself, above the valves. To avoid confusion, OHC engines are not referred to as OHV despite also having their valves in the head. In early 1894, Rudolf Diesel's second Diesel engine prototype was built with a cylinder head featuring push rods, rocker arms, and poppet valves. Diesel had published this design in 1893. In 1896, U.S. patent 563,140, awarded to William F. Davis, illustrated a gasoline engine with the same head configuration, patenting his solution to the problem of how to cool the head, which problem had made the overhead valve engine difficult before then. Henry Ford's Quadricycle of 1896 had valves in the head, with push rods for exhaust valves only, the intake using suction valves. In 1898, Detroit bicycle manufacturer Walter Lorenzo Marr built a motor-trike with a one-cylinder OHV engine with push rods for both exhaust and intake. In 1900, David Buick hired Marr as chief engineer at the Buick Auto-Vim and Power Company in Detroit, where he worked until 1902. Marr's engine employed pushrod-actuated rocker arms, which in turn pushed valves parallel to the pistons. Marr left Buick briefly to start his own automobile company in 1902, the Marr Auto-Car, and made a handful of cars with overhead valve engines, before coming back to Buick in 1904. The OHV engine was patented in 1902 (awarded 1904) by Buick's second chief engineer Eugene Richard, at the Buick Manufacturing Company, precursor to the Buick Motor Company. The world's first production overhead valve internal combustion engine was put into the first production Buick automobile, the 1904 Model B, which used a 2-cylinder Flat twin engine, with 2 valves in each head. The engine was designed by Marr and David Buick. Eugene Richard of the Buick Manufacturing Company was awarded US Patent #771,095 in 1904 for the valve in head engine. It included rocker arms and push rods, a water jacket for the head which communicated with the one in the cylinder block, and lifters pushed by a camshaft with a 2-to-1 gearing ratio to the crankshaft. Arthur Chevrolet was awarded US Patent #1,744,526 for an adapter that could be applied to an existing engine, thus transforming it into an Overhead Valve Engine. The Wright Brothers built their own airplane engines, and starting in 1906, they used overhead valves for both exhaust and intake, with push rods and rocker arms for the exhaust valves only, the intake valves being 'automatic suction' valves. They even built a V-8 engine with this valve configuration in 1910. In 1949, Oldsmobile introduced the Rocket V8, the first V-8 engine with OHV's to be produced on a wide scale. General Motors is the world's largest pushrod engine producer, producing I4, V6 and V8 pushrod engines. Most other companies use overhead cams. Nowadays, automotive use of side-valves has virtually disappeared, and valves are almost all 'overhead'. However, most are now driven more directly by the overhead camshaft system. Few pushrod-type engines remain in production outside of the United States market. This is in part a result of some countries passing laws to tax engines based on displacement, because displacement is somewhat related to the emissions and fuel efficiency of an automobile. This has given OHC engines a regulatory advantage in those countries, which resulted in few manufacturers wanting to design both OHV and OHC engines. However, in 2002, Chrysler introduced a new pushrod engine: a 5.7-litre Hemi engine. The new Chrysler Hemi engine presents advanced features such as variable displacement technology and has been a popular option with buyers. The Hemi was on the Ward's 10 Best Engines list for 2003 through 2007. Chrysler also produced the world's first production variable-valve OHV engine with independent intake and exhaust phasing. The system is called CamInCam, and was first used in the 600 horsepower (447 kW) SRT-10 engine for the 2008 Dodge Viper. Early air-cooled OHV BMW boxer motorcycle engines had long pushrods and a single centrally-mounted camshaft; but the post-1992 BMW R259 'Oilhead' boxer engines had a camshaft in each cylinder head, located between the combustion chamber and the rocker arms. The pushrods were very short, allowing higher rpm and more power. For instance, the BMW R1100S (which had a R259 engine) could achieve an output of 98 hp (73 kW) at 8,400 rpm, with no risk of valve bounce. Since 2013, BMW flat-twin motorcycle engines have had OHC valve actuation.