I have an 853 Bobcat with a kubota engine. One of the guys was running it the other day and started hearing a loud knock/bang sound. It was very low on oil. I am assuming the engine is shot. The one thing I don't understand is that the knock only starts after the engine has been running for a few minutes. When it is first started it sounds ok. Any thoughts on why this is? Any advice on where to look for a replacement engine? Thank for any help.