AOPA Pilot Magazine - July 2024 - 84

RUDDER & WRENCH
Measure of valve and
seat reccesion
Valve guide
Valve seat recession
is a major area of
concern with unleaded
fuel. Hardened valve
seats are supposed to
alleviate the problem.
However, the University
of North Dakota's
engines experienced
widespread recession
despite being hardened.
Valve
Valve seat insert
Valve and seat
recessed
Valve and seat
normal
in GAMI's current challenges. While the
ASTM standard does give some assurances
to fuel providers, proper liability protection
is still an issue.
Braly dismissed the paper's concerns
and said the distributors he's spoken with
aren't concerned about G100UL's safety.
GAMI initially pursued ASTM certification,
a lengthy and expensive path
separate from the STC approval received
from the FAA. While the STC process
involves only the company and the FAA,
ASTM is an industry consensus standard
where competitors come together to create
protocols and approve applicants. There
are controls in place that are designed to
protect the applicant's intellectual property.
However, after some initial meetings
and an application with ASTM, Braly
alleges that an oil company attempted to
file patents on GAMI's candidate fuel, at
which point he abandoned the process.
Swift UL94
Some pilots are understandably skeptical
of switching to an unleaded fuel for fear
of what it will mean for their engines and
safety. Some of those fears were confirmed
recently, when after operating Swift Fuel's
ASTM-approved UL94 for 46,000 hours,
the University of North Dakota late last
year was forced to revert back to 100LL
84
AOPA PILOT / July 2024
because of numerous valve issues. The
university had made the switch to UL94
in its Piper Archers and Seminoles last
summer to bolster support for unleaded
fuels. The fuel has an ASTM approval,
an STC from the FAA, and is approved
by Lycoming for use in the Archer's
IO-360 engine.
School maintenance technicians first
learned of a problem when an Archer
returned to the school's Grand Forks
base with a rough-running engine. Dan
Kasowski, the head of maintenance, said
they removed the cylinder and found valve
seat recession. " At that point it was a oneoff
and we didn't think much of it, " he said.
The discovery of a second recessed valve
seat soon after spurred them to report
the issue to Lycoming and Swift Fuels
representatives.
A full inspection program revealed
issues with 135 cylinders, many of them
with recessed valve seats. Lead has long
been known to prevent valve seat recession,
but the transition to unleaded auto
fuel taught engine makers that hardened
valve seats can prevent the problem.
UND's Lycoming engines have hardened
valve seats.
In a statement, Lycoming said,
" Lycoming Engines conducted a root cause
analysis of this issue, including further
testing of UL94. This analysis has determined
that the engine components and
airframe components conform to specification
and are not believed to contribute to
valve seat recession " . It goes on, " Analysis
indicates that aromatic concentration tolerances
for UL94 may contribute to valve
seat recession in certain flight profiles.
Aromatic limits are not directly specified
by ASTM D7547, and elevated aromatic
concentration may result in slower flame
speed, radiant heat from particulates, and
particulate abrasiveness to valve seats that
may contribute to valve seat recession. "
In other words, Lycoming blames
Swift, and in a rebuttal, Swift CEO Chris
D'Acosta blames Lycoming. " Lycoming's
press release on the root-cause analysis
of UND's issue with exhaust valve recession
is at best inconclusive. High aromatic
hydrocarbon concentrations in UL94 are
not the culprit in this analysis. Moderate
use of toluene (typically 10 to 20 percent)
in the fuel is entirely reasonable and not
likely to contribute to valve seat recession. "
One of the challenges of transitioning
to an unleaded fuel is getting the octane
high enough to prevent detonation. At 94
octane, the Swift fuel is lower than avgas,
which has been suggested is a problem on
the engine's 8.5:1 cylinders. Lycoming and
Swift alluded to the detonation question in
AOPA Pilot Magazine - July 2024

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