[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?

[ed boersma]

I went about it a bit different.

Used a length of 1/2" round SS bar inserted into the pushrod hole, ground out metal until I just touched the bar along most of the length (height of the runner), then 'repaired' the breakthrough with 1/2" brass tube held in place with epoxy and threadlocker. That way I knew that all runners would be very close to the same, and would probably be widened out as much as possible.

Just a thought.

[screamingchief]

It's really not that complicated to avoid breaking thru if your goal is to not do so.

There have been more than a few threads here with folks posting their methods to gauge the distance/thickness of the bulge,one guy fabbed up a real nice fixture to do that,I saved a pic for reference it was so nice.

As stated most of these methods use some sort of solid round stock or such in the tube to measure the inside pushrod wall location when doing this.

But in the end if you go this route your still kinda at the mercy of the castings your working on as far as where the precise port widths are gonna end up as core shift may have one set of heads with lots of room and another set with next to none.

But there are a lot of good threads and info in the archives if you take the time to dig for it.

[Jim Hand]

HD,,
See my response on Classical Pontiac. It basically states to not risk a breakthrough! That part of the port is not a major restriction.

Jim Hand