The engine came installed in the plane with the cowl cut out and all. I know there is nothing wrong with the fuel system in the plane as it ran the same way on the bench. As far as breaking the engine, is states in the manual that no break in is required however I did run about a tank of fuel through it just to be sure. I tried removing the needle limiters on the HSN and LSN and adjusted them for hours trying to get it to run as well as trying different glow plugs and different fuel. I called Horizon and they said it sounded like bad bearings to them and to send it in as it was still within the two year warranty period. After about a week and a half I called to check the status of the repair and guess what? They said almost every part was replaced including both bearings and they still couldn't get it to run correctly so they sent me a new engine. This one is the 46 NX as the NT has been discontinued. As far as the cowling is concerned there is a largish area around the muffler so the heat can escape. Anyway if this engine doesn't work out I'll go with a Saito 62. My older H9 cub with a Saito 56 flies great and sounds so nice. I almost forgot to say what awesome support Horizon Hobby has.