Windy City Weapons

[4thcoast]

Hello all, my name is Stephanie Fansler and I am a student of Mark’s. I learned a few months ago that I would be a part of the Henderson rebuild team, and have since been acquainted with and cultivating my affection for Henderson(s). These past several months have been my inception into, what I consider, a new world. With no background in mechanics, just a yearning “to know”, I had just bid farewell to four years of music school, where I had been wrapping my mind around the theory behind why a secondary dominant built on the fourth degree of a C major scale alludes to the key of B flat major, and wrapping my hands around my Stradivarius, B-flat, piston-valved trumpet. Let’s just say the words, “piston” and “valve”, have obtained quite a new significance.
Now versed in reading a micrometer, and getting the swing of snap gauges, I get to practice my precision measuring skills, which are essential if this engine is to be repaired and mended to it’s utmost potential. Here we go. Valve guides numbered, “ 1 E, 1 I, 2 E…”. Check. Cylinders lined up nice and neat on the workbench, valves standing at attention in two columns of four; four intake, four exhaust. Mr. Hill points out that holding the valve so as to view it from the top of the stem, you can see the subtle difference in stem diameter, the exhaust diameter being larger, (.344”) and the intake smaller, (.312”). I notice that the old valve stems have a pinhole where a .125” (1/8”) pin is inserted, and the new stems don’t. We get to make these holes for the spring retention pin. I think, “Sweet!” I get to spend some extra time in the machine shop, watching Mr. Miller and Mr. Hill gently drill a hole at the top of the valve stem that begins .1406” (9/64”) from the top surface of the valve stem. We go right down the line measuring their external diameters, which have to be machined “down” by the process of turning on Mr. Miller’s HAAS CNC lathes up the hall. With the original valve guide O.D reading .565” we get a consistent reading of .584” for the whole lot. Considering the .001” interference fit into the .500” valve guide orifice, which is necessary in the reassembly of these components, this means that we need to turn .018” from the valve guide(s), leaving the diameter of the guide at .566”, (pretty damn close the original, huh?) or .001” larger than the diameter of the guide orifice. In order for this to all go down, Mr. Hills says, someone needs to draw up a print for Mr. Miller to read. I’m thinking to myself how great it is to be practicing for my machine class in engine power & transmission class, and that this “crossover” is conveniently supplementary. As time elapses and new knowledge saturates, the true understanding of how frustrating it would be to grasp and become engaged in this project if I wasn’t taking my machine processes class…well? Saturates. Alright, last few measurements. Valve stem to valve guide clearance. Eight measurements total; 4 intake, 4 exhaust. From measuring the O.D of the valve stems and the I.D of the valve guides, we calculate out a consistent .004” clearance for the exhaust, and an unvarying .003” clearance for the intake. I write my numbers down, and start to put the Henderson’s organs back on the cart.
March 12th, we are several weeks into the semester, buckling down in Engine Power & Transmission lab, where the ambition of the Henderson project finally emerges, and valves guide the way.