It sounds to me that it may be gummed up a bit. I would saturate it with after run oil or GM trans fluid (Not Ford Type F) Put a prop on it and rotate the engine for a while. The engine should loosen up, if it is still tight at the top of the stroke this is a good thing and probably does not have a lot of run time on it. The engine should run providing you have a good glo plug and fresh fuel. This is a bushing engine and you should not expect AX 46 power from it. I have one and it runs great propped correctly with 10% nitro. This is an ABC engine, look up OS engines on Google and it will provide you with a wealth of info...
-Tom