Valve lash refers to the slop in the valve train before the cam opens the valve. Which option best describes this?

• A. Tension in the 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 the valve stem

Answer: (B)

Valve lash is the clearance or play inside the valve train that exists when the valve is seated, before the cam lobe begins to push the follower and start moving the valve. This slack must be taken up by the cam as it ramps up before the valve actually opens, so it describes the slop in the valve train prior to valve motion. The other ideas aren’t describing that same train clearance: tension in the timing belt is about belt drive tension, not valve train slack; clearance between the valve and its seat is about sealing when the valve is closed, not the train’s play; wear in the valve stem is a wear condition that can change lash but isn’t the definition of lash itself.