AOPA Pilot Magazine - March 2019 - 96

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SAVVY MAINTENANCE

revived engine. For this, I recommend operating the engine as if you'd just replaced
the cylinders (see "Savvy Maintenance:
Breaking Good," January 2019 AOPA Pilot).
Run it hard for at least an hour.
INSPECTION

You'll notice that I haven't mentioned doing
a borescope inspection of the engine before
first start. That's intentional. Inspecting a
long-sitting engine prior to first start won't
tell you much. If you borescope the cylinders, you're almost certain to see light surface
rust on the cylinder walls (assuming they're
steel and not chrome- or nickel-plated), but
you won't be able to tell the degree of corrosion pitting until that surface rust has been
scraped off and the underlying surface made
visible. If you can work the borescope into the
crankcase to view some cam lobes, you'll run
into the same problem. That's why I recommend doing a borescope inspection after the
engine has run awhile.
Borescoping the cylinders after the first
flight or two is a no-brainer. You can use a
cheap rigid borescope such as the ViVidia
Ablescope VA-400 to inspect the cylinder
walls for evidence of corrosion pitting, vertical scoring, and the presence or absence of
visible crosshatch microfinish. Also inspect
the exhaust valves for evidence of asymmetry indicative of leaking and burning.
Inspecting the cam and lifters with a
borescope can range from easy to nearimpossible depending on what engine you
have. The easiest to inspect are Continental
engines with sandcast-style crankcases-
those with a front-mounted oil cooler and
a rear-mounted, belt-driven alternator. For
those engines, it's a cinch to insert a borescope into the crankcase through the oil filler
port and work it past the crankshaft to view
the frontmost three cam lobes and four lifters.
Continentals with Permold-style crankcases-with front-mounted, gear-driven
alternator and rear-mounted oil cooler-
are tougher to inspect. The easiest way is
to remove the alternator and insert a borescope through the crankshaft ring gear to
view the frontmost cam lobes and lifters.
If you have a flexible borescope with a thin
probe, it's possible (although a bit tricky)
to perform the inspection by removing the
7/8-inch timing plug from the left side of
96 | AOPA PILOT March 2019

THE CAM AND LIFTERS on a Lycoming may

be inspected by inserting a thin flexible
borescope up through the oil drain port
and the narrow slots in the bottom rear of
the crankcase.

the crankcase nose (opposite the alternator) and do the same thing.
Lycomings are the toughest to inspect.
Many say that it's impossible to look at the
cam or lifters without removing cylinders.
That's not quite true. If you drain the oil
and use the oil drain port to insert a flexible borescope with a probe that's no more
than 5.5 millimeters in diameter (such as the
ViVidia VA-350 ), it's possible to work it up
through the slots in the bottom rear of the
crankcase and past the crankshaft to visualize the rearmost three cam lobes and four
tappets located above the crank.
Alternatively, you can just fly the engine,
do frequent oil changes (e.g., every 25
hours), and cut open and carefully inspect
the oil filter with a magnet for the presence
of significant quantities of ferrous metal.
Inspect any such metal found under magnification. Spalled tappets usually throw off
small and irregularly shaped flakes, while
spalled cam lobes usually produce fine
metal whiskers. If you're able to get through
the first 100 hours without seeing significant ferrous metal in the oil filter, you can
probably relax and conclude your resurrected engine dodged the bullet.
AOPA
MIKE BUSCH is an A&P/IA.
EMAIL mike.busch@savvyaviator.com

www.savvyaviation.com

http://www.aopa.org/pilotguides http://www.savvyaviation.com

AOPA Pilot Magazine - March 2019

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