1983 300Sd Engine turns but will not start. Symptons were
1) the glow plug light takes about 5 seconds to come on stays on for a few seconds and then goes out. After 21 seconds I hear a click. Does this sound normal?
2) Had some nailing. Ran Diesel Purge through. Ran great for a few days and then the slight nailing came back at low speeds.

I intend to change the glow plugs (about 80,000 miles on them)and relay along with the injectors (over 100,000 miles) should there be anything else I need to be looking at? Valve adjustment or timing chain?

There's no need to change anything until you have done some diagnosis. This is just throwing money and parts at the car sort of like the government. They have a problem, they just start throwing money at it without first analyzing the cause of the problem.

First check to see that you are getting voltage to the glow plugs. If you are, replace the glow plugs, not the relay, if you aren't, check the bar fuse inside the glow plug relay.

I would not change the injectors until you get the car started and then see where you're at.

Good luck,

To dove-tail on both what Larry said as well as PEH in an earlier post, be sure to troubleshoot first, and with glow plugs be sure to un-plug the large connector on the GP relay in order to accurately test each plug. I had always tested them improperly by not removing this connector and it made all the plugs test good when in fact they weren't.
Good luck,
Adam

Thank you for the help. Electrical problems always get me nervous. I never tested the glow plugs before. Where do I start and how do I go about doing it. Also How bad do one or all of the glow plugs have to be before the car would not start?