Picked up a super clean 84 with 106,000 and just changed the oil / filter. It now has a knock when warm ? didn't do it before . Coincidence that something went ? Starts right up, runs smooth. Help please

 

If you just bought the rig, the po might have loaded the engine with an oil additive to hide the noise.

 

my first thought also. put about 500 or so then did the change + plugs ,wires, cap, rotor. Put in a wixs filter with 10W40, then just for giggles swapped that for a 20w40 and then some lucas and still the noise ? but only after it warms up ? cold start nice and quiet ? any other input ?

 

Can you isolate where it's coming from? Top of the motor/front/ bottom end. I hope for your sake its not in the bottom. You can use anything from a long screwdriver to listen or a stethoscope. Look for moving/dangerous/hot/electrical parts first before trying anything. Then if you do the long screw driver method like my hillbilly self does place the tip of the screw driver on what you want to listen to and then put your ear to the handle (once again look for hazards). and listen. If you need instructions for stethoscope operation then you might not be able to use them and should refer to hillbilly method . Sorry bad joke.
But isolating he noise would be a great helping you narrow down your possibility's for what might be wrong.
.