Sarge,
You get your first plane and engine, hear a couple guys at the local field say they don't like ABC engines, and suddenly you're an expert.

Sorry, but the break in on an ABC engine is typically one or two tanks of fuel. The break in on a ringed engine, when done properly, is a couple of GALLONS of fuel.

Aerobender,
True ABC engines are aluminum (A) pistons in a chrome (C) plated brass (B) sleeve. But many advertised ABC engines actually have a nickel plated sleeve and should be sold as ABN's. These are state of the art engine technology, and are big sellers primarily BECAUSE they need little break in, which can often times be done in the air.

Here's why, ABC engines are constructed with a tapered cylinder wall (no ring) so that the piston gets very tight at top dead center when they're cold. As the engine heats up, the differing rates of expansion provide the proper clearance between piston and cylinder wall.

If the engine is run too rich, it stays too cool (and too tight) which wears away the cylinder wall resulting in lower compression (not a good thing).

So, the BEST way to break one in is with a series of short (about one minute) runs at just below peak rpm (which quickly gets the engine to opewrating temps), followed by a cool down period of a few minutes; then repeat. I'd run at least a tank through it on the ground like this, then set it for about 500 to 600 rpm below peak and go fly!

Manufacturers will give different break in methods, but the typical one recommended is to run the engine on the rich side for a tank or so, then set it to normal conditions for flight. Personally, I think you run the risk of wearing away too much cylinder wall this way, but....

Now, I recommended the Thunder Tiger 46 Pro because I've never heard anything bad about them. The same is true of the OS 46 FX (which was recently replaced by the AX). The AX isn't quite as good as the FX, but it's much more expensive than the Thunder Tiger.

There are a number of other good 46's out there, but I'd stay away from MDS (Multiple Dead Sticks, as the joke goes), or the OS 46 LA. I have a 46 LA and it's been a decent engine, but many have had problems with them.

46's are recommended mainly because they're powerful enough to be useful in sportier, more aerobatic second planes, but are not really overkill for a 40 size trainer. The LT-40 will handle the extra power without problems. (A friend in our club has one with an OS 70 four stroke, talk about overkill! )

Anyway, you're taking your time and being selective, so I'm sure you'll do fine with whatever you choose.
Dennis-