ok...the engine has started to knock. Started tractor, after about 30 seconds it started knocking. Oil pressue was at 50 psi. what the heck gives? hour meter is around 4700 hours. Where does one go for parts, bearings, etc for rebuilding. Its a gas engine.Waukesha. Seen something about pulling pto shaft to remove engine from frame. Mine has 540/1000 pto case on rear. Still need to pull pto shaft? don't see where that shaft aligns with engine crank centerline??!!?? unless theres a pto shaft under upper plate cover on pto case.