A pushrod is a simple yet essential part of any reciprocating engine. Its purpose is to transfer linear motion from the camshaft to the pistons, which in turn convert it into rotational motion that powers the crankshaft. In order for an engine to function properly, the pushrods must be correctly sized and installed so that they can withstand the extreme temperatures and pressures inside the cylinder head.
The vast majority of engines use overhead valves (OHV), which means that the camshaft is located above the cylinders. The pushrods are responsible for actuating the valves via rocker arms; when a lobe on the camshaft opens a valve, it also pushes on the end of the pushrod, which in turn pushes on the rocker arm. The rocker arm then pivots and opens or closes the valve.
Pushrods are typically made from high-strength steel alloy, and they come in various diameters depending on engine size and design. Some engines have adjustable pushrods, which allows for fine-tuning of valve clearance (the distance between the tips of the valves and their respective seats). Properly adjusted valves are critical to engine performance and longevity.
Engines with overhead camshafts (OHC) do not use pushrods; instead, their camshafts are directly connected to each valve via bucket tappets or roller followers. This arrangement is more compact and lighter weight than an OHV design, but it generally requires more frequent maintenance due to higher operating temperatures and greater valvetrain noise.