AOPA Pilot Magazine - June 2014 - 89

P&E

OWNERSHIP

Anatomy of a valve failure
ASI poster for aircraft engine shops
B Y D AV E H I R S C H M A N

Burned exhaust valves have long been
a leading cause of cylinder failures
and power loss in piston aircraft
engines. Modern borescopes allow
us to look deep inside cylinders-and
this guide will help you interpret what
you see through the viewfinder.

OVERVIEw: Valves that fail to seat properly are subject to
severe and uneven heating that can cause them to weaken
and fail in predictable patterns.

HeAT
DisTRiBuTion
CHART

GREEN MEANs stOp

pROGREssION OF FAILING VALVEs

First indication: Circular color pattern is
slightly uneven and nonsymmetrical.

Crescent-shape, discolored burn pattern
developing at upper edge.

Burn pattern migrates inward.

Crack

GREEN MEANs stOp. The green area
at the top shows this valve should be
replaced immediately. (Note how the
uneven burn patterns match the heat
distribution chart.)

Green crescent progresses toward
center with valve cracking and failure
a serious danger.

Crack at 12 o'clock shows valve failure
is imminent.

BURNEd pIzzAs ARE OK
COLORFUL BUt HEALtHY

NEW, DIGITAL BORESCOPES allow aircraft mechanics
to thoroughly inspect the inner workings of piston
engines without removing cylinders, but who knows
how to interpret the images they see?
Adrian Eichhorn, a pilot and mechanic who pioneered the use of medical imaging technology for
aircraft engines, has his own method for evaluating failure-prone exhaust valves, and he's sharing it
with the help of the AOPA Foundation's Air Safety
Institute (ASI). Eichhorn and ASI have created a
poster, "Anatomy of a Valve Failure," that shows an
exhaust valve as it approaches a potentially catastrophic failure.
With financial support from pilots and aircraft
owners to the AOPA Foundation, ASI designed and
printed the posters and is distributing them free
to aircraft engine shops and maintenance schools
throughout North America.
"Both Lycoming and Continental valves share
certain similarities in how they are designed, how
they work, and what they look like before they fail,"
Eichhorn said. "I've examined hundreds of valves
using medical technology, and the patterns are easy
to recognize. You've just got to know what to look
for."
Eichhorn said he's seen no correlation between
valve wear and whether an engine is operated rich
or lean of peak EGTs. The keys to valve longevity, he
said, are for pilots to keep cylinder head temperatures
within normal limits, and for mechanics to periodically check for proper valve seating.
Burn patterns are subtle at first, with slight discoloration near the edges. The patterns become more
pronounced and the scorched portions of the valves
develop a green hue. "Green means stop on exhaust
valves," Eichhorn said. "If a portion turns green, it's
time to replace the valve. There's no reason to go
beyond that point."
If allowed to progress, the green portion will reach
deeper toward the center of the valve. In advanced
cases, two green portions will appear on opposite edges of a valve as hot gas from the combustion
chamber reaches around it. In the final stage before a

LEARN MORE:
www.airsafetyinstitute.org/valves
Special thanks to Adrian Eichhorn
and Dr. Peter Wu.

Don't be alarmed by the
bright color, or deposits
around the edges. The
symmetrical pattern shows
this valve is just fine.

A symmetrical, circular
pattern shows a healthy
valve. Red and orange
deposits are harmless.

Thick lead deposits from an
overly rich mixture give this
healthy valve the appearance
of an overcooked pizza.

FUNDED BY GENEROUS DONATIONS TO THE AOPA FOUNDATION
AOPAFOUNDATION.ORG

potentially disastrous failure, cracks can appear in the
valves and the edges turn a steely color.
"What you're seeing is the valve eroding," Eichhorn
said. "The erosion prevents the valve from seating properly, and that accelerates its demise."
AOPA
EMAIL dave.hirschman@aopa.org

WEB

www.airsafetyinstitute.org/valves

www.aopa.org/pilot AOPA PILOT | 89

http://www.airsafetyinstitute.org/valves http://www.airsafetyinstitute.org/valves http://www.AOPAFOUNDATION.ORG http://www.airsafetyinstitute.org/valves http://www.aopa.org/pilot

AOPA Pilot Magazine - June 2014

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