The consensus around here is that as long as the engines are blessed by
the mechanics and checked for compression, one can exceed the
recommended TBO sometimes by a factor of 2x.

My question is this: Is this practice safe?

I'm no expert, but it is NOT safe. There are things deep in the engine that
a mechanic has no idea about...such as...the main bearing. If one of those
goes, so does the engine.

As far as cylinders, pistons, rings, valves go...well...they can be
monitored and you can get a "Top Overhaul" to keep those components in
working order. BUT it's the bottom half that really needs the Major
Overhaul. The bearings, seals, crankshaft, cam shaft, connecting rods that
can and will cause an engine failure.

Going over TBO by 50 to 100 hours is one thing...but 1000 or 2000 is totally
an unacceptable risk.

My partner and I fund an Engine Account with 17.00 dollars per hobbs flying
hour. We have 12,000.00 dollars in that account now with 800 hours left to
go. When we hit 2000 we will have 90% or more of the money for an overhaul.

Don't stick your head in the sand and fly, fly, fly and never save for the
overhaul. You'll only be fooling yourself that when the time comes you'll
have the money or that you'll get 4000 hours out of that engine. It won't
happen. The next time you blink you'll be at TBO and no way to replace the
engine. Then you'll be forced to sell the plane for much less than you
bought it for.

Kobra