Valve Seats

Effect: Valve burnt out locally in a deep channel or gutter.

Cause: Poor seating due to cold sticking; lack of tappet clearance; excessive carbon buildup; misalignment; worn valve guides; pre-ignition; etc.

Effect: Wide areas of valve face burnt and blowing but no guttering.

Cause: Poor valve seating in affected areas; worn guides; excess material removed from and during previous re-facing operations.

Effect: Badly pitted valve and valve seat faces, discovered on early overhaul due to power loss or a burn out.

Cause: Excessive oil consumption, incorrect mixture setting producing a high level of solid particles or long periods of low power cold running.

Effect: Exhaust valve underhead or back of head surface corrosion.

Cause: Excessive overload and overheating or incorrect fuel.

Effect: A hole burnt through the back of head in the underhead radius, just behind the seating face.

Cause: This is another form of the radial rim crack (Head Fractures) or thermal fatigue, burning through beyond the hard seat face.