AOPA Pilot Magazine - June 2021 - 93

limits, although the valve guides were worn.
All six cylinders were reused after re-valving and honing them.
" These engines could easily have
gone another 1,000 hours without breaking a sweat, " the engine shop owner said.
" Whatever you've been doing with these
engines, keep doing it. " At that moment, I
vowed that I'd never again allow my engines
to be torn down without a compelling reason.
A COMPELLING REASON

I flew those engines uneventfully until they
reached TBO again (1,400 since major overhaul) and kept going. They were still doing
fine when they reached 200 percent of TBO
(2,800 SMOH).
Finally, at about 3,300 SMOH one of
the pistons in the right engine experienced
a freak fatigue fracture that caused it to drop
half of the piston skirt into the oil sump. On
its way there, the liberated piece of piston
skirt tangled with the spinning crankshaft
(and lost), so it arrived at the sump as a
bunch of marble-sized chunks of aluminum.
I was cruising at 11,000 feet over
the Nevada desert when this happened.
Interestingly, the engine didn't quit. It
didn't stop making power. It didn't even
shake noticeably. In fact, it ran amazingly
well despite its underweight and lopsided
piston. Ultimately, I decided to shut it
down and make a one-engine landing in
Las Vegas, but had I been flying a single
I'd have had no problem landing the airplane under power.
I considered just dropping the sump and
cleaning out all those pellets, but after due
consideration I decided this incident was the
compelling reason I'd been waiting for. I sent
my right engine off to a good engine shop for
a major overhaul. It was time.
True to my vow, I did not overhaul the
3,300 SMOH left engine since it wasn't contaminated and was still running fine. As a
compromise, I decided to replace all six cylinders (which by now had more than 5,000
hours on them) and all six pistons (which
came from the same batch as the one that
failed in the other engine). I also had all six
connecting rods fit with new bearings and
bushings. But the engine never came out of
the airplane and the case was never split.
Five years later, this left engine is still flying

and showing every indication of still being
happy and healthy.
FRANK'S TEACHABLE MOMENT

In 2001, my friend Frank bought an early
Cirrus SR22 powered by a Continental
IO-550-N engine with a published TBO of
2,000 hours. When Frank's engine started
to approach this time-in-service that
Continental's high priest had etched on a
stone tablet, I encouraged him to keep flying.
At 2,190 hours, during an annual inspection, Frank's A&P/IA reported that two of
the six cylinders had tiny cracks developing
between the top spark plug hole and the fuel
nozzle. Cracks in this location are common
with these cylinders and are not particularly
consequential-they never have caused any
sort of catastrophic cylinder failure-so I
would be inclined to keep an eye on them to
make sure they don't grow larger or exhibit
signs of fuel seepage. But Frank's IA insisted
the two cylinders needed to be replaced.
At this point, Frank did something radical-something I tried but failed to persuade
him not to do. He had his mechanic remove
the engine from the airplane, crate it up,
and ship it to a respected engine overhaul
shop in Tulsa, Oklahoma. Frank instructed
the engine shop to remove all six cylinders,
inspect the cam and other bottom-end components visible with the cylinders removed,
and advise him what needed to be done.
I considered this a gross overreaction to
a trivial inspection finding and told Frank as
much. In hindsight, it was probably indicative of Frank's nervousness about going over
TBO, something I can identify with.
The engine shop did as Frank instructed
and advised him that the cylinder head cracks
his IA was so concerned about were not really
cracks at all, just minor cosmetic casting flaws
that could be polished out easily. The cylinder
barrels had very little wear. The bottom-end
components looked great. The pistons were
a bit dirty and a couple of the oil control rings
were fouled with lead sludge, but otherwise
there was really nothing wrong with the
engine. The shop cleaned and re-ringed the
pistons, honed and re-valved the cylinders, put
the engine back together, and shipped it back
to Frank's mechanic.
This was Frank's teachable moment. He
took the vow.
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AOPA Pilot Magazine - June 2021

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