What causes a pushrod to fall out?

Answer 1

In an OHV -over head valve- engine the pushrod is contained on one end by a valve lifter which is running up and down on the cam lobes, and on the other side by a rocker arm, which is transfering that force to the valve stem. Three things could cause the pushrod to be able to move out of its position and fall into the recesses of the engine.

1.wear- the pushrod ends, the spring inside the valve lifter, the rocker arm pivot point and wear points on valve stem side and pushrod pocket side, as well as the surface the rocker arm mounts to, and the valve stem end. These surfaces can wear and result in too much slop in the valve train, and when the valves are moving, the rod can find its way out of place. If the spring inside a lifter wears out and breaks, as soon as the oil pressure drops there will be enough room for the rod to escape on the next start.(assumes hydraulic lifters)

2.misadjustment- If valve lash adjustment is performed incorrectly, the rocker arm may become loose during its up down cycle, causing the rod to walk off, or damage may actually occur causing the rod to spit out. If the rocker arm mounting stud or nut is not torqued correctly, this can cause the rod to be lost

3.damage- If any of the components above have been damaged or have hairline fractures (common on stamped rocker arms) or are otherwise bent or deformed, it will impossible to maintain the proper clearances

David W.

Career Mechanic