"JFLEISC" wrote in message
...
Several years ago I bought a '61 straight back for my wife and was shy
about
the 0-300. Since then I've grown to love it. It does run smooth and all
her
instructors rave about it. For some reason the plane is unusually quick
also.
Climb is average.
1. What kind of fuel burn do you consistently get with an O-300? Is
the generally reported 105 KIAS @ 8 GPH true?
At 105 KIAS I actually think it's a little better, maybe 7GPH.

2. Does the autogas STC help reduce the problem with valve sticking?
If you have the STC, do you generally burn a mix?
Got the STC and been burning pure regular. It runs noticably better (and
considerably cheaper) but we are agressive about applying carb heat even
though
I have never felt a trace of ice. The guy who sold it to me said it never
saw
auto gas. Used a lot of oil so I took the top end apart. Only one valve
was
slightly close to snug but 3 of 6 cylinders had one or more frozen rings
from
carbon and goo. The cylinders mic-ed up within spec. (An A&P told me the
older
cylinders were great but the new ones are too soft. How do I know?) Put
new
rings on and now the engine is running sweet. This was the first thing
done to
it in 1800 hours.

3.In general, has your experience led you to expect to have to do a
top overhaul about halfway through the TBO period? What are the
ballpark costs of such an operation.
The ring job, 1 wrist pin, 2 valve guides and a gasket set cost me a tick
over
$400.

4. In your opinion, would it be worth it to pay the premium to buy an
new 172 equipped with the O-320E2D?
My biggest bitch is that those Continentals seem impossible to stop from
leaking oil. The Lyc. in my other plane is always dry.

Some leak, some don't. Most do but not much. I am flying a friend's 172
at the time which is just absolutely a joyful experience. It's a '56 172
with the straight tail and that great Johnson bar between the seats. It
gets off and climbs with a vengeance and the O-300 runs wonderfully. Great
sound too and smoooooth. A 4-banger Lycoming never ran this smooth. My
first experience with an O-300 was in a ragwing 170, and I was instantly in
love.

I'm restoring another 172 which I have flown too, O-300 engine also, but
this one is a '66 and needs cylinders. So what? You can buy cylinder
kits today for half what you could buy them for ten years ago, thanks to
competition among TCM, ECI, and Superior. The cylinders don't always last
to TBO but the bottom end is very durable and solid. I know of a trusty
O-300 in an old 172 nearby with over 2300 hours on the bottom end and still
running strong. He's busted TBO by over 500 hours.

To extend the life of the cylinders I would lean carefully and monitor cht
and egt religiously. Change oil every 25 hours. And make power changes
smoothly, gradually. I'd also watch the baffling, avoid 100LL except as a
mix of 10% avgas and 90% mogas because the low-compression engine is not
designed for high-leaded, hi-octane gas like 100LL. Fly regularly and no
cold starts below freezing temperatures. A good oil filter is a must. I'd
also use an additive to leech out lead fouling and carbon deposits and keep
the plugs cleaned and gapped. Watch your mag timing. I firmly believe
that MMO and Alcor TCP are helpful (one or the other), especially in the
O-300 using avgas, to keep valves from sticking. Read more about these
great engines in the 172 forum in Yahoogroups. The current discussion is
about MMO and its obvious benefits. I don't need graphs, charts,
engineering reports and so-called hard data and statistical studies to
convince me MMO is desirable. And, btw, I put a capful of MMO in my
Harley's tank every fillup back in the 70's as advised by H-D Motor Company.

And finally, if you haven't flown Continental's six bangers, including the
O-300 and its grandbaby, the IO-360, you just THINK you've flown an
aircraft.