Valve lash refers to which of the following?

• A. Slop in timing belt
• B. Slop in the valve train before the cam opens the valve
• C. Clearance between valve and seat when closed
• D. Wear in valve stem

Answer: (B)

Valve lash is the clearance in the valve train when the valve is fully closed and the parts aren’t loaded. It’s the slop before the cam lobe starts to push on the follower/rocker and open the valve. This gap exists to accommodate manufacturing tolerances and thermal expansion, so the valve train doesn’t bind as parts heat up. When the cam lobe begins to move, that lash is taken up and the valve starts to open. If the lash is too large, valve timing becomes imprecise and the engine can run rough or lose efficiency; if it’s too small, the parts can contact each other and wear or seize. The other options describe different things (belt slack, valve-to-seat clearance, or wear), not the defined clearance in the valve train before the valve opens.