Valve clearance

Valve clearance, or valve lash, is a small gap between the cam and the bucket tappet, or between the rocker arm and the valve stem tip, when the valve is closed. It allows for heat expansion and makes sure the valve can shut completely on its seat.

Too little clearance can stop the valve closing fully, causing hard starting, power loss and burnt valves, particularly exhaust valves. Too much clearance causes noisy ticking and slightly reduced valve lift. On many engines, clearances get tighter over time as valves and seats wear.

Clearance is measured with feeler gauges on a cold engine, with the cylinder at TDC on compression. It is adjusted with shims or with a screw and locknut. Follow the intervals and values in your service manual.