Good news: Many of the newest compo-
nents are retrofittable to the older engines.
This brings us to the topic, “What do I look
for in a used O-200?”
Used (and used-up) O-200s are plentiful at Reno, since the Formula One racers
wear things out at a prodigious rate. While
4000-plus rpm is not a normal operating
range for most of us, it’s encouraging that
racing has proven that the O-200 is one
strong little engine. Racers and crew members helped sort it out.
Certain stock components (pistons,
cylinders, valves, and springs) can last at
those speeds provided they’re selected,
prepared, matched, and balanced exactly
and correctly. Continental makes good
parts: The rods, for instance, are all shot-peened at the factory and are durable.
Amateurs frequently try to lighten the
rods…and then they break.
evaluating a used engine
If the used engine you want is runable, pull
the spark plugs and see if there are any
signs of detonation or bridging, carbon
buildup, or oil. Use a borescope (or at least
a tiny mirror on a stick and a light) to check
for obvious scratches or gouges. Check the
compression and do a leak-down test.
Before you test-run it, look at the oil. Is it
filthy, sticky, or smelly? Autopsy the oil
filter (but first offer to pay for a new one
and an oil change, in the event that you
don’t buy the engine). Examine the logbook. Are there a lot of entries in the same
ink and handwriting, but perhaps dated
over several years? (Hey, it happens.)
Crankshaft run-out is sometimes overlooked. A little end play is not often a
problem, but any other crank anomalies are
bad news. Prop flange wobble or radial run-out generally signify trouble—you’re likely
buying a core, not an engine.
A hot tip for those who are experiencing
objectionable oil blowby: The Cessna
Aerobat uses a modified breather elbow
(part number 633182) that draws from a
“cleaner” spot in the crankcase. You can
make a similar one by drilling out the existing threaded end and brazing in a thin-wall
tube about 2 inches long. (This author, of
course, assumes no responsibility!)
The racers agree that any and every used
case needs to be sent to a reputable shop for
a full remanufacture. The studs on earlier
cases sometimes get loose; top shops fix this
with heli-coils (a repair or upgrade that’s
okay with the FAA but not recommended by
the factory). Newer cylinders have the
Stellite exhaust seats and flow better than
the earliest ones, due to smaller-diameter
valve stems. The newest cylinders are best of
all, according to the factory and those racers
who are saving up for them.
One thing that seems to be non-func-tional on a lot of old engines is the oil
temperature probe. Its design invites
destruction, so use care when removing
it. Another item: When you rebuild, use
the newer spring-loaded pushrod tubes.
These won’t leak like the older swaged
design does.
