Valve Damage Part 3 Breakage

BREAKAGE

Contributing Factors:
a) Use of inadequate valve material
b) Engine overspeed. Valve float
c) Weak valve springs
d) High seating speed
e) Abnormal combustion
f) Incorrect fuel *

Result: The valve head breaks, along a chord of its circle, by the under head radius (the fracture starts with a fissure in the radius)

Contributing Factors:
a) Engine overspeed
b) Excessive accumulated heat in the valve neck.
c) Weak springs. Valve float.
d) Seating speed too high due to excessive lash.

Result: Breakage in the middle of the under head radius with total valve head detachment

Contributing Factors:
a) Thermal shock
b) Engine overload
c) Excessive combustion temperature and pressure
d) Weak valve springs
e) Too high seating speed

Result: A radial crack inward from the margin. If the fissure advances, the head will break.

Contributing Factors:
a) Weak springs. Valve float
b) Engine overspeed.
c) Seating speed too high due to excessive lash.
d) Incorrect valve timing.
e) Sticking valve stem.
f) Guide/seat misalignment.

Result: Valve head to stem breakage

FATIGUE FAILURE
Starting point
Note: Breakage by material fatigue happens after thousands of cycles, starting in a small defect and advancing until breakage occurs.

Contributing Factors:
a) Defective keeper assembly
b) Keeper groove damaged
c) Valve float
d) Excessive valve train clearance
e) Engine overspeed, especially on valves with rectangular keeper grooves.

Result: Valve stem breakage in the keeper groove area