Toyota Repair: 5s-fe making tapping noises after top overhaul, top overhaul, camshafts

Question
Sent car for top overhaul.  Changed distributor.

After overhaul, the car sounds like a diesel engine.  A tapping noise is coming from from the engine block, next to the timing belt.  THe mech changed the tappets and exhaust valves during the overhaul.  The mech is at a loss.  He is now talking about camshafts or cylinder being off.

What is the problem?

Answer
This engine uses a "silent gear" design for the camshafts, one of the camshafts has a two piece gear that is spring loaded, before disassembing a service bolt has to be installed into the two piece gear to keep the spring from unwinding, if the bolt is not installed and the camshaft gear loses the preload on the gear the engine will sound just like you said, a diesel. If this is the case the camshaft has to be removed and and preloaded by turning the smaller part of the gear until the hole in the gear lines up with the threads in the main gear and inserting a short 6mm thread size bolt, once the camshaft is reinstalled the service bolt is removed.