How is valve lash adjustment performed?

How is valve lash adjustment performed?

• A. With the valve open
• B. With the lifter removed
• C. With the cam lobe at peak
• D. With the valve closed

Answer: (D)

Valve lash is the clearance between the valve stem and the rocker (or lifter) when the valve is fully closed and seated in its valve seat. You set this clearance with the valve closed because that is when the valve, valve spring, and rocker are in a settled, unloaded state, giving the true, intended gap. If you try to measure or adjust while the valve is open or with the cam lobe lifting the lifter (at peak), the gap is changing dynamically and won’t reflect the correct lash. Removing the lifter would also disturb the mechanism and wouldn’t show the real clearance. So the adjustment is performed with the valve closed (cam lobe on the base circle).

Valve lash is the clearance between the valve stem and the rocker (or lifter) when the valve is fully closed and seated in its valve seat. You set this clearance with the valve closed because that is when the valve, valve spring, and rocker are in a settled, unloaded state, giving the true, intended gap. If you try to measure or adjust while the valve is open or with the cam lobe lifting the lifter (at peak), the gap is changing dynamically and won’t reflect the correct lash. Removing the lifter would also disturb the mechanism and wouldn’t show the real clearance. So the adjustment is performed with the valve closed (cam lobe on the base circle).