I have been working on my 39 B for a couple years. It ran great up to yesterday. I got it out this weekend to do some cleanup and paint prep. I let it run for about 5 minutes and all of a sudden it had a metallic ping and smoke started rolling out of the crankcase breather. I tried to shut it down but I was too far away before it ground to a stop. I pulled the crankcase cover and let the smoke go out. I checked the oil pump and it was spinning. The valves were working correctly and the rods were tight. The motor spins freely and has great compression. I don't feel any resistance when spinning it over by hand. I changed the oil and no pieces or chunks of metal came out. Long story short is I have no oil pressure and one heck of a knock coming from the pulley side of the engine. I don't see the part AA824R on the top of the oil filter housing. The parts book and service manual don't explain how the spring is installed. Any insight on what it could be? I'm thinking mains.