Definition: OHC is an acronym for a design of 4-stroke engine where the camshaft is located in the cylinder head. Some engines deploy a double over head cam (DOHC) where the inlet and exhaust camshafts are separate. This design allows for a more direct operation of valve opening.

Examples: The Suzuki GS750/1000 series engines use a DOHC system. The camshaft lobes operate onto a shim located inside a bucket which is positioned over the valve.

Various sizes of shims are available to give the correct running clearance.