how do you test a cylinder head to see if it has a crack or do you have to take to someone to find out.

 

First off checking for any cylinder head warping you can take a good straight edge and lay against the head and check using feeler gauges.Shouldn't be able to pass any gauge under the straight edge.For a general test of leaking valves just fill the intake port then the exhaust port with carb cleaner or a solvent such as naptha and see if any seepage around valves.If it seeps then lapping valves or possible seat or valve replacement may be needed. For possible cracks in head areas such as coolant passages,seats,etc magnafuxing is the most common way to tell.You can purchase a powder type or spray type dye that can spot cracks invisible to the naked eye at most auto stores. Plus here's a video on using powder on an old engine head that shows up cracks.