Pushrod

A pushrod is a slender rod used in certain internal combustion engines to transmit linear motion from the camshaft to a valve actuation mechanism. In engines with a cam-in-block design, the camshaft sits in the engine block and its lobes push lifters. The pushrod then transfers that vertical motion up to the rocker arm, which converts it into the opening and closing of the intake or exhaust valve against a valve spring.

Function and operation: As the camshaft lobe lifts the lifter, the pushrod pushes the rocker arm through its end, causing the rocker to rotate and press on the valve stem. When the lobe passes, the lifter drops and the valve closes under spring force. This system synchronizes valve timing with piston movement in engines that use a camshaft in the block or overhead-valve designs.

Design and materials: Pushrods are typically made from steel alloy and may be solid or hollow to reduce weight while maintaining stiffness. The ends are shaped to interface with the lifter cup and the rocker arm, and the length and diameter are selected to preserve correct valve timing and motion. Some engines use adjustable pushrods to fine-tune valve lash and geometry, though hydraulic lifter systems can reduce or eliminate the need for manual lash adjustment. Modern overhead cam (DOHC) engines generally do not use pushrods.

Applications and context: Pushrods are common in traditional V8 and other engines that employ an in-block or overhead-valve design. They are less common in engines with directly actuated camshafts on the cylinder head (DOHC). In addition to automotive use, similar pushrod components appear in other mechanical linkages where linear motion must be transmitted between inclined or separated components.

Maintenance: Pushrods can bend or wear at interfaces, especially if lubrication is inadequate or valves are misadjusted. Routine inspection focuses on straightness, end wear, and related valve train performance.