Knucklehead Porting Aid

 

One of the things that will quickly jump out at anyone who sets out to port a set of knuckle heads is the chunk of casting that protrudes into the bowl of the intake port. That protruding section of the casting houses the threads for one of the head bolts, specifically the one that's between the two cylinders closest to the intake spigot. Unfortunately, it also happens to be in a key area which limits airflow. 

Arrow indicates the casting "lug" as found in a stock port

 When porting, generally speaking, the more of this chunk you can remove the more you can improve the airflow. However, grinding through into the threads is, . . . well, let's just say grinding through is problematic. If only there was a easy way to check how much material there is between the port and the heads if for no other reason just to cut down on the anxiety while you're grinding.

Well, as to happens there is one. Here's a little tool I rigged up that you're free to copy if it will help you out.

 The idea for this tool came from a You Tube video by legendary engine builder John Kasse. It's really just a scaled down version of a home-made tool he featured in one of his tech tips. This one is obviously modified to fit this specific task, but it's worth mentioning that the same concept could also be adapted for checking the thickness of cylinders that have been bored oversize multiple times which would be particularly useful on Knucklehead cylinders. Build it to the right dimensions and checking the thickness between the fins and the cylinder bore would be a snap rather than a guess.

The simple concept behind the tool is that as long as it's built symmetrically and with the pivot centered properly, the thickness of whatever the points on one end close down upon will give you a visual of that thickness on the other end.

                                   The tool in action on a dual carb OEM Knuck casting that has                                       already had a considerable amount of the lug removed

 For checking the Knuck head at this one particular spot, one of the straight arms has to be trimmed so it will slide into the head bolt hole (be sure to trim the "outside" edge and not the "measuring" edge) and also shortened just a bit so it can bottom out in the hole. One thing that you'll soon learn when using the tool is that as you grind material from the boss in the port, the material will get thinner at deepest part of the head bolt hole first. That's fortunate because it is the part of the hole that can most afford to be weakened and if you do grind through, it's still possible to repair the mistake.

And no, the picture is not of a Swastika.