That's just broke off in the engine mount, you should be able to use a back out tool that you can get at a hardware store and get it out, but it has nothing to do with the engine itself. The engine just sits on the two engine mounts. You could try running it with just 3 screws, but it might cause the engine to shift and therefore causing you to strip a spur gear, then again, you might be able to run it for weeks and not have any problems. If you don't want to mess with trying to get it out, just order some more engine mounts, there not expensive. They're only like $4 on rufaster.com.