As a spill over from my glow days all engines mounted upright were bolted to the top of the engine bearers, yet engines mounted inverted were bolted to the underside of the engine bearers. I suppose I just followed the crowd in doing so, and switching to gassers did not pose a problem as most all were rear mounted. Now that many of the smaller gas engines are beam mounted like most all of their glow counterparts, is ther any reason why an inverted engine should not be mounted on the top of the bearers.

Karol

Yes, it will probably mess up your engine centerline.  Also, remember that mounting ears are usually machined on one side to be parallel and flat for mounting.  The cast tops are not square, and you could risk distorting the case and ruining the engine.

I know on smaller engines, you could move the centerline up to 1/4" by mounting it on the "wrong" side of the ears.  If the ears are thicker on the gasser, and I'm assuming they are, it could put your centerline off even more.  So your cowl won't line up correctly( assuming enclosed engine), or even worse, could create an evil handling plane because the thrust line isn't correct.

I have never seen what you describe. When I mount an engine inverted, the engine mount is also inverted, thus the relationship of engine to mount stays the same. The top of the beam mount should be lined up with the center line of the firewall: inverted should be the same alignment.

I try to match up the carb to the fuel tank location, along the center line. Whether you use the top of the engine bearers or the bottom is really immaterial as it works either way well. But the engine has to match up with the front of the plane and the center line for the fuel tank as much as possible.  A lot of the RC combat guys mount the engine upright on the bottom of the engine bearers as it just seems more natural to do so.
Now there are a few engine designs that don't have as much room on top of the engine lugs for mounting on the bottom like that, but those are the exception.

I've never bolted them to the tops of the flanges. Up side down, sideways, or angled. Always mounted to the bottom of the flanges, with gas the tank position is not important, as the carb is a pumper.

All of my gas engines mount on spacers/pillars perpendicular to the firewall.  With glow, I invert or tip the engine mount along with the engine so it is a constant mating. 

I think the last model I had with built-in wood engine bearer blocks was my Trainer 40 built from RCM plans.

no matter the orientation, the crank centreline is always on the thrust line for the fuselage.<div>Thrustline is closely coupled to the wing centreline. changing this relationship makes it much more tricky to trim the aircraft.</div>