What is Valve Lash

What exactly is lash and how does it affect your engine? Lash is the clearance or play between adjacent movable mechanical parts. In terms of valve lash it is the distance between the tip of the rocker arm and the tip of the valve. Valve lash is a crucial element to a proper running engine since it insures that the valves in the heads open and close as designed.

Just like Goldilocks and the three bears, there are three lash conditions: to loose, to tight and just right. Loose lash will have an increased gap between the rocker arm and valve. This will cause more of the lift in the cam to be used to close the distance and reduce the amount of lift transferred to the valve. Valves that do not open all the way cannot draw the full charge of fuel into the cylinder nor can it expel the burnt gasses on the exhaust stroke. Tight lash on the other hand will not allow the valves to close completely which also reduces the efficiency of the engine to get fresh fuel in and burnt fuel out. In extreme conditions and on high compression engines this can possibly cause the valve to come in contact with the piston, which is never a good situation. When the valve lash is set correctly, the camshaft, lifters, pushrods, rocker arms and valves all become one harmonious unit which will allow your engine to run at its optimal performance level.