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Although an overhead camshaft (OHC) engine also has overhead valves, the common usage of the term "overhead valve engine" is limited to engines where the camshaft is located in the engine block. In these traditional OHV engines, the motion of the camshaft is transferred using pushrods (hence the term "pushrod engine") and rocker arms to operate ...
Roller rockers can also be used in overhead cam engines (OHC). However, these generally have the roller at the point where the cam lobe contacts the rocker, rather than where the rocker contacts the valve stem. Some OHC engines employ short rocker arms, also known as finger followers, [2] in which the cam lobe pushes downward on the back of the ...
This reduced inertia in OHC engines results in less valve float at higher engine speeds (RPM). [1] A downside is that the system used to drive the camshaft (usually a timing chain in modern engines) is more complex in an OHC engine, such as the 4-chain valvetrain of the Audi 3.2 or the 2 meter chain on Ford cammers. Another disadvantage of OHC ...
On most overhead valve (OHV) engines, proper clearance between the camshaft and tappet is achieved by turning a set screw in the end of the rocker arm that contacts the end of the pushrod until a desired gap is achieved using a feeler gauge. Too large a gap results in wear from misaligned parts and compromised engine performance, and too small ...
Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft (located in the engine block) to the valves (located in the cylinder head). The bottom end of a pushrod is mated to a lifter, upon which the camshaft makes contact. The camshaft lobe moves the lifter upwards, which moves the pushrod.
In 1994, all 2.2-liter engines were updated to sequential multi-port fuel injection and power increased to 120 hp (89 kW), with torque increasing to 140 lb⋅ft (190 N⋅m). The MPFI and SFI versions produced enough power to allow the 2.2 to replace the old Pontiac Iron Duke engine as the 4-cylinder offering in the S/T trucks and A-body cars.
The lobed camshaft rhythmically presses against the lifter, which transmits the motion to the engine valve in one of two ways: through a pushrod which actuates the valve via a rocker mechanism (in an overhead valve (OHV) engine); via direct contact with the valve stem or rocker arm (in an overhead camshaft (OHC) configuration).
Also pushrod engines almost always make less power and torque from a given displacement, compare just about any engine you can find: BMW M3 - 81.875 ft-lb/l, LS7 - 67 ft-lb/l. Also compare the output of the OHC Ford engines to the GM pushrod engines, the Fords have higher torque output for a given displacement.