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Most OHC engines drive the camshaft or camshafts using a timing belt, a chain, or multiple chains. These systems require the use of tensioners, which add complexity. In contrast, an OHV engine has the camshaft positioned close to the crankshaft, which may be driven by a much shorter chain or even direct gear connection.
This contrasts the earlier overhead valve engine (OHV) and flathead engine configurations, where the camshaft is located down in the engine block. The valves in both OHC and OHV engines are located above the combustion chamber; however an OHV engine requires pushrods and rocker arms to transfer the motion from the camshaft up to the valves ...
Considered advanced by Detroit engineering standards at the time, the Pontiac OHC 6 followed the Jeep Tornado I6 as the second post-World War II domestic-developed and mass-produced overhead cam automobile engine. [6] The Pontiac's single camshaft was supported by journals within the aluminum valve cover; no separate bearing shells were used.
All of this is side-show to what I said, that OHV engines (though more complex) are intrinsically more reliable than OHC engines. OHV can safely be drip or splash fed with oil (sometimes pushed through hollow pushrods without assistance from the oil pump). Whereas OHC engines have spinning bearings, so they're much more dependent on lubrication.
A single camshaft located in the engine block uses pushrods and rocker arms to actuate all the valves. OHV engines are typically more compact than equivalent OHC engines, and fewer parts mean cheaper production, but they have largely been replaced by OHC designs, except in some American V8 engines.
Some engines, such as the Fiat Twin Cam engine of 1964, began as OHV engines with an oil pump driven from a conventional camshaft in the cylinder block. When the twin overhead cam engine was developed, the previous oil pump arrangement was retained and the camshaft became a shortened stub shaft.
The engine was discontinued in 2003, replaced by the 2.2-liter DOHC Ecotec engine. Although it displaces 134 cu. in, the 2.2-liter OHV is still commonly referred to as the GM 122 today, and has been reputed for its simplicity, reliability, and ease of maintenance in the J-body cars and S-series trucks, and a few L-body cars.
OHC engines always have fewer parts when comparing systems with the same number of valves and cylinders (4 cylinder 2 valve OHC engine to 4 cylinder 2 valve OHV engine). Though it is true that some OHC engines do come close to the high moving part count of an OHV engine it is very rare. The Honda SOHC C series V6 engines for example had a ...
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