Most likely the cylinder head gasket is leaking but the head doesn't necessarily have to be machined. First it needs to be cleaned up with an air tool and abrasive disc, and it has to have the proper "surface finish" for the new gasket to bite into. Next, it has to be checked for flatness. An engine machine shop can do that for you. Unless the manufacturer specifies differently, the standard is no more than .005 inches variation in any direction on a cast iron head, and no more than .002 inches in any direction on an aluminum head. I'm sorry I don't know how that translates into millimeters, but your engine machinist will know what is acceptable. They can also check the head for cracks. They use a feeler gauge and a precision straightedge to measure the flatness. .005 inches is roughly the thickness of two sheets of paper. If the head needs to be machined, they will leave it with the correct surface finish.
Jan 9, 2014 at 3:12 PM
