How would I go about removing this?

 

really?

It's the oil fill neck. Twisting and pulling would remove it.

 

Sometimes they're pretty tight. I clamped some roughly contoured wood (by me ) to it with a large hose clamp to get extra pulling, prying, and twisting force. Used a dead blow to get it loose initially. Be careful though, it's pretty thin metal.

 

you should be able to tap it out by the flange if its stubborn, then when you re-install it put a very small amount of RTV on the outside and tap it in.

 

http://www.rebuildingrotaryengines.c...ng_Resurfacing

5 mins in... shows how.