I have a 1991 Honda Civic DX. It has run well until last week when it just wouldn't start for me. I have checked a few things: I have spark on all four plugs, the fuel pump seems to be working as it should, the starter is turning the motor over... although it doesn't sound right.
I checked compression on the cylinders and found only around 40 -50 psi per cylinder.

My question is does this sound like a head gasket problem? The car was running completely normal... just seems kind of sudden for a gasket? I am by no means a mechanic, but usually if I know what needs to be replaced I can make my own repairs.
Any suggestions would be greatly appreciated!
Thanks in advance

Look for antifreeze in the oil. From what I know if it is present then the problem may be a cracked head or something else.

No anti freeze in the oil...
Got to thinking... Would the timing being off effect the compression? Ei valves open on compression stroke.
Should I be checking timing before I start tearing my engine down?

Is it smoking at all, if so it could be the piston rings. The timing should not go off all of a sudden without something to affect it. My wife's car had that happen with one cylinder and it was the head. If I had to guess that would be my suspission. Before you go through the trouble of putting a gasket on you should have your head tested.

You could also call your local dealer and ask for the service department and ask them the same question. I do it all the time.

It hasn't been burning oil/ smoking. I'm going to pull the cover off the timiing belt to see what I see.

Reading this might help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-honda-civics-46563-2.html#post232786

Minimum compression should be 130 psi.