G'day

I have run in many engines in my time but I have never run an engine in inverted. Some have been mounted sideways or even at 225 degrees but never inverted (180 degrees).

The main reason I would not run in an engine inverted is simply that it is too easy to flood an engine when it is inverted and especially when you don't know the engine at all. A flooded inverted engine is not fun and broken conrods are a possibility if you manage to get a hydraulic lock and use an electric starter.

My most recent two new engines were a Saito 40 and an OS 81 alpha. The Saito is now mounted inverted and is running fine. I spent about 20 minutes running it in a test stand and then moved it to its small Tiger Moth and completed its running in in the air. The OS spent about 20 minutes in the test stand and then another 10 in the plane being run to get the tuning right before its first flight. In both cases, the time spent with the engine in the stand meant that once it was in the model, I knew how much to prime and I had no problems with starting or running.

So ...

I'd suggest you get to know your new engine in your test stand and when you are happy that you can start it easily and have it tuned, then put it in the plane and go flying.

Cheers.

Mike in Oz