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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.
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