Just picked up a new to me four door, I got it with a "blown head gasket"(oil in the water, I also know it was over heated badly) it runs ok, down on power but smooth, and has no blow by from the oil filler cap. Trying do decide wether to just do a head gasket, or full rebuild. So I did a compression test 115 psi warm +/- 5 added oil and only got 120 +/- 5 psi, so what do you think valves? Rings? Crank key? Full rebuild or just throw a head gasket on and hope for the best? Other diagnostic ideas? Thanks

With only a 5psi difference between wet & dry tests, it's unlikely to be past the rings - I would check the valve clearances, and then follow that with an inspection of the cam timing and crank keyway - if those are all correct, do a leak down test - that will give you some idea where you're losing pressure - past the valves, or into the cooling system (via head gasket or a crack somewhere).

Ok thanks, I'll start there, how do you tell if the valves are burned, visually while I have the head off?

That is one way, but, the leak down test, which I presume you're going to do before pulling the head, will also allow you to determine if the leak is past the valves.

I would rent a leek down test and check valves before pulling the head, but I have to pull the head anyhow as it is pumping engine oil into the cooling system, so I am grateful for the suggestion, but the head needs to come off unless someone knows what else would cause oil in the coolant? It's 1.6 16v

Oil in the coolant ...

 - head gasket
 - cracked block - which is not unusual with the G16 engines
 - cracked head

Coolant in the oil ...

 - head gasket
 - cracked block
 - cracked head - there may also be a welch plug in the head that can allow cross contamination
 - intake manifold - either gasket or cracked

Is it an automatic transmission?  What are the chances of it being atf in the coolant rather than engine oil?

How much do you want to spend - are you looking for a low buck repair?

Because of the uniform low compression, and the fact that there is no significant change when oil is added, my suspicion is the cam timing is incorrect, possibly because of a damaged keyway - I would check that as step one - if you get lucky and it's just incorrectly set timing, setting it correctly will bring the numbers up, and you can then get a better idea of the condition of the rings (another wet & dry compression test).

If you get decent compression numbers after correcting the timing, pull the head, check the valves by filling the bowls with kerosene and see if it leaks out - if not - slap a gasket in and call it done.

No it's a 5spd, but thanks for the tip on the kerosene! I'll try that. I'm waiting for a water pump and timing set before I tear it down. Hopefully this weekend!

I would also suspect a bad crankshaft keyway.