Welcome to the site, you could probably get more response to your question by posting it on the engine forum. As these engines are becoming more rare, the are becoming more expensive to repair and maintain. My question for you is this. Is the engine doing what it is supposed to? Is it performing at close to it's rated HP? If not you need to look at why, and if there is a problem, correct it first. If you know the recent engine history, you might have a better idea of what you can get away with, as for as the pump. Otherwise, I would absolutely not touch the pump, until I had looked at the crankshaft bearings. You might contact fjh, one of the members, he could probably answer questions you have about this engine. James