Valve clearance

The gap is measured with feeler gauges with the engine cold and the piston at top dead centre on the compression stroke. Intake and exhaust have different values; the values and check interval are in the owner's manual.

• Too little clearance: the valve does not close fully; compression drops, starting gets hard and the valve can burn.
• Too much clearance: ticking from the top of the engine, and the valves open late.
• It is adjusted with a screw on screw-type rockers, or by fitting a shim of different thickness on bucket-and-shim engines.