Pull valve cover for #3, remove both rocker arms for #3, pull the spark plug and apply compressed air (100lbs) into the cylinder #3, listen for a air leak sound in the exhaust tail pipe, Intake manifold or crankcase.
Exhaust= Exhaust valve problem
Intake= Intake valve problem
Crankcase= Piston ring failure
Two more things can cause low compression, ...
Why would you expect smoke in the exhaust? Any smoke from that cylinder can be combusted by the other hot exhaust gasses in the exhaust manifold.
You have a clear indication of a problem in one particular cylinder.
Your next step is to consider applying compressed air to the cylinder through the plug hole and then listening for where it comes out. Do make ...