60 PSI in all 4 cylinders

So here's my issue. I rebuilt the engine in my b2200 7500 miles ago. 200 miles ago I replaced the head with a brand new one and did the conversion to mechanical rockers from HLA's. I'm running a Pace Setter header and a Weber carb. Just before replacing the head I had the cam plug pop out of the rear of the head and dump all my oil on the freeway. Since installing the new head the cam plug has popped out 4 more times. I have a block across it holding the plug in for now and everything seems to be running fine at good rpms and not noticing any difference in performance, but the radiator has been pushing all the coolant to the overflow without the engine even being hot. I replaced the radiator cap and still getting the same result. This leads me to believe that my radiator is being pressurized. So next I performed a compression test. All 4 cylinders were exactly the same at 60 PSI. I would lean towards head gasket if it was at 60 in 1 or 2 of the cylinders but all 4 being the same is making me scratch my head. The pressure to the radiator makes me curious of a crack in the block but that still wouldn't tell me why I am only getting half compression in all 4 cylinders. I am in the process of building a 302 for the old girl but until the build is complete this is my commuter car. Any suggestions on the cam plug issue, compression issue, or radiator issue would be appreciated (pretty sure they're all related though). Thanks

I would first suspect the gauge is flaky and not going up past 60psi if the engine is working otherwise. Minimum on the trucks is something like 110. The throttle should be open all the way while you crank the motor. Crank the motor about 5 revolutions per cylinder. That is for a dry test.

Put a couple of squirts of oil in a cylinder you are testing and see what your reading is then. That is a wet test.

The stock motors have a bar that is supposed to go over the rear cam plug to keep it from pushing out.

Maybe your rings got stuck on the pistons with all the oil being pumped out, but if the truck is not smoking or knocking I wouldn't really think so.
Do you have a working pcv or is it just vented. That can cause excess pressure in the crankcase, and maybe that is why the cam plug is being pushed out.

I have to agree... something was done wrong.
You won't easily get an engine to run if compression is below 90 psi on all cylinders.

Thanks for your responses guys. I have looked at all the trucks in the scrap yards and at all my friends' mazdas and none of them have the bar you are talking about. It does have an extra threaded hole back there thought that I was going to put a large fender washer on to hold the plug in since the other side is being held buy the stock pick point that is mounted on the back of the head and I think between the 2 it would be fairly secure. As for the gauge, I used 3 different guages. 2 of the screw in style (one digital and the other a needle) and 1 of the ones that you just push against the spark plug hole. We checked my buddy's truck at the same time and he was getting between 115 and 120 so I know they go up that high. Even when I have the engine hot the compression doesn't get into the hundreds. As for the PCV, it is working fine, I can blow through it and when I shake it the check moves freely. The thing I haven't tried is holding the throttle open while I crank or conducting a wet test like Mr. Tweaker mentioned, going to do that in the morning. It is interesting though since it purs like a kitten. I'll let you guys know what happens. Thanks again for your ideas.

OK, there is a plate that holds the plug in, I have one and seen it many times on other trucks - a lot of people just leave them off and never have trouble - but I have had trouble without it in the past. I totally agree that you may have a crankcase pressure problem and if it is not the PCV system (notice I said "system" not just the valve) then you are looking for something more serious. But that doesn't seem to be your main concern right now...

I always say a compression test is not very conclusive no matter what it reads - what you need is a leak down or at least just a pressure hose, put 120PSI into the cylinders (while they are at TDC) and see where your leak is. Also test them at BDC if you can (might require loosening off the rockers) that can tell you if you had a crack lower in the bore.

Also pressurize the cooling system and see what up.

Your coolant being pushed out is most likely a result of combustion pressure making it's way into your cooling system (even a small leak can do it) because combustion pressure is astronomically higher than your cooling system pressure, it does not take much to blow your cap and push all the coolant out - now this combustion pressure can only really get out in a few ways:

-Blown headgasket (how sure are you that you observed ALL of the correct procedures and what brand gasket and lots did you use)

- Cracked block or head (you bought a new head - I have used them too and they are really good, so I doubt it's that - although anything can happen)

Another note - if you have coolant being pushed out AND you have excessive crankcase pressure, then it sounds like possibly you have combustion pressure going into oil and water systems.