1991 Pick up 4 cyl problems

[trick240sx]

Hello I need help. I have a 1991 Nissan PU. I started hearing a severe knock in the engine and pulled the valve cover. I noticed 4 of the valves have play in them. I also noticed that the old timing chain tensioner was totally gone accept for a plastic ring. I put it in the shop and they did the timing chain tensioner sprockets and all. When I picked the truck up the tapping was still there and the truck had less power than when I took it in. Now the truck keeps shutting off I took the oil cap off with the truck running and it appears that oil is not getting to the top of the engine Basically I need help.

1. Is there suppose to be oil under the valve cover if so how much.

2. Is it possible that the plastic from the tensioner clogged the oil pump and oil pump pickup.

3. Is there anything else that would cause the valve to act up.

also if I do drive it valves will not tap under load at first and then you hear a loud tapping after a while is that oil starvations.

[NISTECH]

You need to take it back to the shop and ask them what the heck happened first.