On most OHV engines, the adjustment was made by turning a screw set in the end of the rocker that pressed on the end of the pushrod. With the engine rotated to give the widest gap between the camshaft and a particular tappet, the rocker screw was adjusted until this gap was at the correct spacing, as measured with the use of a feeler gauge. If the gap was too wide, this could result in an audible 'tappet rattle' from the rocker cover. If the gap was too narrow, this could result in engine damage such as bent pushrods or burnt valves. The adjusting screw was locked by a locknut. Failure of the locknut to hold the adjustment in place could cause catastrophic engine failure, which has led to fatal aircraft crashes.