The relief at at the rear of the crank-case becomes a "port" if the cylinder head is rotated to configure the engine for rear exhaust. If you purchased the engine through Triad Aviation Ken, I will swap you for another one if you would like, no problem. I must admit that we don't open every single engine up and inspect it like Dar does, but the ones we have inspected have been perfect. The engines are hand assembled and such a large piece of metal should not have been overlooked. On the other hand if you choose to clean it up yourself and get on with flying the engine, please accept my appologies on behalf of the factory. If you can get a better picture of the engine and the peice of swarf you removed I will pass it back to the factory and see that someone gets smacked with a trout.