[harddecisions]

The last time I ported a set of 5C heads I broke through the pushrod bulge on one cylinder. Before I started grinding on the 5C heads I averaged the stock side to side dimension of the intake port at 0.950 at the smallest part just inside the intake manifold flange. This is a rough measurement and is probably not precise to all heads. I measured this clearance with a snap gage keeping the handle of the snap gage perpendicular to the intake flange. As I ground out material I would slide the snap gage, which I had locked at 1.050 in and out of the port. My plan was to increase the dimension by 0.100 on all four intake ports both the heads. As I said I broke into the pushrod hole on one cylinder. No big deal, I repaired the hole with ½” brass tubing from a hobby store sealed with JB Weld and everything was fine. Now I have started porting a set of 6X heads and have decided to flatten the pushrod bulge to a side to side measurement of 1.030 to prevent breaking into the pushrod hole. Needless to say the ports end up being larger than 1.030 but I use that as a reference to keep from breaking through. I completed grinding on all eight ports and didn’t break though on any cylinder. Obviously I want the ports as efficient and straight as possible or I wouldn’t be porting the heads. I read the comment in either Jim Hand’s book or the HO Specialties book about judging the thickness of material by placing a 3/8” extension in the pushrod hole to check clearance. Sorry, but I don’t remember which book and don’t want to look it up right now. This advice really didn’t work for me; I can’t judge the clearance well enough to continue cutting deeper into the head. I really have two questions: First does anyone know a good way to measure the thickness of the metal between the intake port and the pushrod hole, and secondly does anyone have better dimension for the side to side clearance that I can work from to smooth the pushrod bulge?