I am helping a bud with his FS 90. On the back cover plate there's an area that is extended and you can see a small bearing go around and there is a flat head screw in the middle. You can see that go around too so it is connected to the crankshaft. My question is that this area is all open and could get dirt in it. Is this original or was there a cap over this that I am missing? Thanks in advance for any help. I hope the pictures show what I am dealing with.

Jeff