When the engine starts making metal, you've got an expensive overhaul on your
hands. Normally, you can get two, sometimes three, major overhauls/repairs (see
another thread for which of these words you want to use) out of the bottom end
before you have to undersize the crank. If you go until the engine makes metal,
and depending on what metal it is, you may not even have a reusable crank when
you pull it apart, and now you are really talking MONEY.

Same for the jugs. If it is pistons that are making metal, then they are
getting loose and sloppy in the bore and this accelerates wear tremendously.
Exhaust valves are in the neighborhood of $200 apiece, and the guides are not
far behind if you have to machine the guide bore.

Wear is not linear. It is exponential, and the longer you go past RTBO, the
further you are up on the exponential curve.

Now, if you are REALLY looking to fly inexpensively, buy a relatively high time
engine, put a couple of hundred hours on it, and then figure out which end of
the wrench gets greasy. Find yourself a mechanic willing to do an "owner
assisted" repair/overhaul. The O-200 is about as bonehead simple as you can
get, and all the machine work is done by an outside facility. You get back
straight/chromed cylinders with the valves installed and lapped, fitted pistons
with fitted rings, case inspected, crank inspected, cam inspected/overhauled,
and the like. You can send out the mags, carb, vacuumpump, and any of the other
accessories you want. From there on it is tinkertoy simple (with expert advice)
to put it back together.

Roughly? Including R&R and labor to dis/assemble? Half.

The HARD part is having the guts to pull it apart yourself. However, with a
digital camera recording every step, putting it back together is a simple
reversal of the process.

Just my 8% of two bits, mindya.

Jim




-Another option I've looked at is purchasing a low price Cessna with an
-engine that's past it's recommended time between major overhaul. Some of the
-sellers I've spoken with are insistent that recomended times aren't
-important, it's the condition of the engine that matters (ie. not making
-metal).

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com