Water in cylinder...head gasket or porous block

[Stuart Giles]

The thinner HC head gasket isn't as tolerant of warpage and waterway corrosion as the early type. Your problem could just be a leak from one of the water passages into the combustion chamber, rather than a 'proper' head gasket blow. checking the flatness (or not) of the cylinder head is simple if you have the head off already. A straight edge can produce misleading results unless it is the 'Camelback' type. A surface plate is the best thing really, but a piece of thick plate glass will do if you don't have access to surface plate. If the block and head are both flat, it's really down to pressure testing the block. you can do this at home if you have access to a compressor with a pressure regulator. The head/block is filled the brim with water and then the air pressure is raised to about 50 PSI. These photos are of a 1920s Chevrolet cylinder head I did a while ago, but I have done the same with A7 blocks. There's nothing more frustrating than  doing a load of work/spending a load of money on a block or head, and discovering that it's only good for a door stop when you come to run the motor up.