OHV pushrod engine

In an OHV (overhead valve) or pushrod engine the valves are in the cylinder head, but the camshaft sits low in the crankcase. The cam lobes push lifters, which push long pushrods up to rocker arms that open the valves.

The design is compact in height, simple and gives strong low-down torque, but the extra mass limits high revs. It is typical of Harley-Davidson big twins, older BMW boxers, Moto Guzzi's classic V-twins and Royal Enfield singles.

Many pushrod engines use hydraulic lifters that need no adjustment; others need regular valve clearance checks at the rocker adjusters. Ticking that comes and goes can be a sign of a lifter or adjustment problem.