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An overhead valve engine, abbreviated (OHV) and sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead (or "sidevalve") engines , where the valves were located below the combustion chamber in the engine block .
OHC cylinder head (for a 1987 Honda D15A3 engine) An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. [1] [2] This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block. [3]
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 rocker arm to open the valve. In such a configuration one end of the follower is anchored (pivoting in place on a roller bearing), rather than having its fulcrum in the center like standard rocker arms.
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.
2.5 L; 152.2 cu in (2,494 cc) inline-5, with two (pushrod-actuated) valves-per-cylinder and indirect fuel injection from either Bosch or Spica. 88 mm × 82 mm (3.46 in × 3.23 in). This engine is a five-cylinder version of the 2-litre HR488, and also uses KKK turbochargers. Applications:
Though it was designed as a pushrod engine, it was advanced for the time. [1] The pushrod version of the Lancia boxer was only ever used in the Flavia, and its derivatives including the Lancia 2000. In 1976, a new overhead cam engine based on a similar layout was designed and brought into production in 2 and 2.5-litre displacements for the Gamma.
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).