Thats a very good and understandable answer Kieth It gives me more confidence to try and source a larger three blade prop for the 120sp, or indeed to not try and get so much out of a 15 x 13 3blade prop on the 90sp. I think that after the initial running in, I was blinkered in to trying to achieve the revs given in the manual, and this may have led to some very hot runs. My 90sp suffered a front bearing failure after a relatively short period, which you repaired under warranty. I flew it for the first time last week in a Hawker Hurricane since it came back from repair and it feels like the bearing has gone again. The engine does seem to run extremely hot, so I'll replace the bearing then treat both the 90sp and the 120sp I'm buying second hand as new engines, and go through the running in process by the book.........and some more! on the bench until I'm happy with them both before trying to fly them in a model again

Thanks,
Walts.