i am confused,i thought i would see a valve with a portion burnt out but it looks o.k . to me,,with the cam off and all valves seated ,head upside down ,i poured a small amount off gas in the compression area, it did not seep through,if the valve was not seating properly wouldn't the gas run through? when the car was running you could feel it blowing out the exhaust pipe,,i guess one question is should i take this head to a shop or try to find another one in the junk yard? thanks,kris

Run the pistons down the bores and feel for vertical scratches that would indicate a broken ring. If the tops of the pistons are covered completely in carbon, and there are no scratches, the rings are fine. If you have any clean aluminum on the piston tops, it is burning oil.
Have a shop do a valve grind if all else is good. A variation of 20 psi on 150 is more than likely cranking time, or some other variable in the test itself, rather than an engine problem.

well , the engine when running had little power,and as i said if i put my hand over the exhaust the blow-out was very forceful as if the engine was pumping air on one stroke, if it was rings i suspect i would see some smoke and there was none, the reason i suggested a junk yard head was the expense involved, the piston top is not clean ...any other ideas?.......Kris

Well Kris now that it is apart, diagnosis can be more difficult. Is the entire piston top clean (or different) from the other three? You may have had a blown head gasket. At this point you will have to ensure the head is good before re-installing it. A junkyard head is no better, and probably worse, than the one you have. Did you check the bores for scratches?

Define "blowing out the exhaust pipe" would you? Why would you junk that head? Your method of checking the valves for seal is about as good as you are going to get without pressure testing them. We have always done just as you are doing only we used windshield washer fluid as it is a little bit thinner.

Mark

For future reference.

Are you saying that if one has the head off, eg. during head gasket change, one can check the valve seals by just turning over the head and seeing if gas/washer fluid leaks through?
--
1980 245 Canadian B21A with SU carb and M46 trans

No, that is not what is meant by that statement. Turn the head over, find two cylinders that are on overlap, i.e. the valves are closed, and fill the combustion chamber with washer solvent. I use the solvent because it is thin and has blue coloring in it. Now look up inside of the ports and look for signs of seepage. You are checking the valve face to valve seat interface. If you see fluid leaking through there then the valve faces need to ground and the seats cut. This is really a down and dirty way to do it and is meant to give you a ball park idea of the condition of the seats. The seals themselves are located on the valve guide and go around the valve stem of the intake valves. Hope this clears it up a little and thanks for asking.

Mark

"Hope this clears it up a little and thanks for asking."
Yep. Neat trick of the trade. Thanks.
--
1980 245 Canadian B21A with SU carb and M46 trans

Did you rule out the possibility of bad rings?

Please clarify what you felt at the exhaust pipe. Virtually anything that could go wrong in a cylinder would cause the burst corresponding to that cylinder to be weaker, not stronger, than the other three cylinders.

If the cylinder walls look good, and the plug was not fouled, and you didn't have other evidence of a blown head gasket (e.g. forcing water out of the cooling system) then look at the cam and intake valve to make sure that the valve was opening and this cylinder was filling with air as it should.

Has anyone adjusted the valves lately? Any chance that one might be too tight and leaks at a certain temperature?