Which component's thickness should be increased to reduce valve lash when it is too large?

• A. Rocker Arm
• B. Cam Gear
• C. Bucket
• D. Valve Stem

Answer: (C)

Valve lash is the clearance between moving parts in the valve train. When lash is too large, the valve won’t start to open promptly as the cam lobe begins to push, leading to late opening and noticeable valve train noise. In engines that use a bucket tappet, the amount of clearance is determined by the thickness of the bucket tappet (and any shim under it). Increasing the bucket’s thickness reduces the gap, bringing the valve actuation back into proper timing.

Rocker arm thickness would alter the geometry of the rocker-to-valve contact and isn’t how lash is adjusted in bucket-tappet designs. Changing cam gear thickness would affect timing between gears, not the valve clearance. Increasing valve stem thickness isn’t a practical adjustment and would create fitment and guidance issues. So, increasing the bucket thickness is the appropriate way to reduce excessive valve lash.