Ford Repair: 360 73 ford truck, main bearing, rear cylinders

Question
Hi James,  My name is Trey & I have a 360 in my truck. I hear a knock in the motor & it sounds like its coming from the rear of the motor. When the truck is at idle it seems as though I can hear it on the same place on the rotation.  When I changed the oil I didnt see any metal; I also checked the flex plate/flywheel.  I only hear it at low rpms, above 1800 I hear nothing.  Can you help me?????

Answer
Stay at low r.p.m's and keep servicing the engine until you find the problem. Were you under the truck while it was running when you checked the flywheel. If so you would have surely heard them if it was torque converter bolts. The problem sounds like the rear main bearing or the connecting rod bearing. Break out a stethoscope. Pay close attention to the rear cylinders of course. With any luck it won't get out of hand and anytime soon since it only does it at an idle. You won't wanna here this but run high test. Let me know what you here with a stethoscope.