knocking sound at idle when warm

[mooktank]

the 5.0 in my truck make a knocking sound sometimes at low rpms when warmed up. Also the oil pressure drops at idle sometimes when warm and at idle as well. It will go back up when I rev the motor up. I really need this engine to make it through the winter and there are hardly any mods on it. 160k though. Oil always changed every 3000. It sounds like a vibration in the truck that only happens when i rev it up and it then comes down and it starts at like 1000 rpm.

 

[Schlodes]

Check your harmomic balancer asap. If the rubber is all cracked, and coming out the sides, it's junk. Unplug the coil wire and have a buddy crank the motor over and look to see if it wobbles... Or worse yet, if it has spun a little bit on rubber [cause the rubber is so worn] then the motor is not balanced now and that 'could' be the knocking you hear.

 

[mooktank]

what about my oil pressure dropping to zero when it makes this sound? Think its a bad oil pump or bearings? I have a 351 to put in it but i was gonna do it next spring, should i do it now?