EXHAUST VALVE DEFECTS

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The following defects apply to most of the cylinder head valves but exhaust valves

are the most prone since they endure the most difficult conditions.

Overheating

•              insufficient cooling

•              afterburning

•              poor combustion

•              overload

•              not reseating fully.

High temperature corrosion

•              associated with high vanadium, sodium and sulphur content of fuel and high metal surface temperatures.

Failure to reseat

•              insufficient tappet clearance

•              excessive expansion due to too high a temperature

•              creep

•              jamming in guide

•              damaged spring

•              distortion of the valve

Impact damage

•              due to heavy seating

•              uneven build up of hard debris on seat.

Abrasive damage

•              due to contaminants in fuel and air

•              hard products of cylinder lub oilcombustion.

•              Any of the above faults can cause the valve to leak leading to gas cutting of valve

•              reduced compression and cylinder power.

and seat. Generally all of the above causes will lead to eventual failure due to overheating of the valve

Indications of leaking valves

•              high exhaust temperature.

•              smoky exhaust.

•              surging of turbocharger.