Compression Question

[BAMM71]

Hey all, long-time lurker here.

I recently acquired a 71 C10 with a 350/3 speed (on the floor). It was, of course, running and driving and then I ripped the exhaust loading it on the trailer...which snapped the manifold...this can go on and on.

It had what I thought was a misfire. Pulled the cap and rotor (HEI) and replaced those, plugs, and wires. The same hitch in the giddy-up was still there. I pulled the plugs and the number 3 plug looked brand new :/ I did the compression test 140-145 in every cylinder and ZERO in number 3. I pulled the valve cover and nothing seemed amiss...turned it over and one spring on intake side wasn't compressing. I hit it with some cleaner and let it soak and then everything was moving properly again. Stuck a cloth in the cylinder and bumped it and the cloth went flying. So confused. I was thinking if it were a hole in the piston I would have no pressure. This is new territory for me but I'm open to thoughts and suggestions and not scared to get dirty.