overhead-camshaft engine

An overhead-camshaft (OHC) engine is a type of internal-combustion engine where the camshaft is positioned above the cylinder head, directly operating the intake and exhaust valves. This design is favored for its ability to achieve higher engine speeds compared to older "cam-in-block" designs, which used pushrods to transfer motion from the camshaft in the engine block to the valves.12

In an OHC engine, the camshaft's irregular disks, called cams, push on the valves to open and close them in a precise sequence synchronized with the piston's movement. This synchronization is crucial for the engine's four-stroke cycle: intake, compression, power, and exhaust. There are two main types of OHC engines: single overhead camshaft (SOHC), with one camshaft for all valves, and double overhead camshaft (DOHC), with separate camshafts for intake and exhaust valves, allowing for more precise timing control.1