Cylinder heads and valves
This simple, brief page literally encompasses almost a year of effort! When I decided to create my own, personalized head design, I also determined that I wanted to learn the art of casting... and it is indeed an art, one that I haven't even come close to mastering. Roughly six months were spent researching sand casting, culminating in a level of comfort with the process, and general confidence with the output. The first attempts at casting were producing perhaps 70% scrap and 30% acceptable product. This improved over a few weeks to the other end of the spectrum; 70% of my attempts were creating nice castings. As the learning curve flattened, I was probably scrapping only 10%.
The design of this head was simple... I first xeroxed Lee's head design, and then used a bit of white-out to eliminate everything except the interior void. In other words, I kept the volume of the head above the piston, and simply redesigned the exterior. The angles, location, etc, of the valves, and the intake and exhaust ports, were retained.
Photo: shows the progression of the cylinder heads, concept to finished head. Upper left is the original wooden pattern. A pattern board was made which casts 4 heads at a time from 356 aluminum alloy. One of those as-cast heads is upper right. Lower left is preliminary machining, including valve stem holes and spark plug hole. Lower right is a completed head, minus rockers or valve stems.
One major change was in the use of an insertable valve stem of aluminum bronze, rather than separate stem bushings and valve seats. This has several major advantages over a valve system which uses pressed seats and valves which ride in bushings...
1) The valve seat (the area which contacts the valve periphery and forms the seal) is machined at the same time as the reamed stem hole. This ensures alignment between valve stem and valve periphery, thus helping with the seal. 2) The stainless valve and the seat area can be ground or lapped outside the head itself. Once the seal is assured, only then is the stem installed in the head with a light press fit. 3) There is no danger of a valve seat popping free and falling into the cylinder. Finally, 4) Valves and their matched stems can be stockpiled as spares and easily used as a unit to replace a fauly valve + stem in a head.
Photo: On the left is a completed aluminum bronze valve stem with a valve loosely inserted. On the right is a valve executed in 303 stainless.. 316 would be a better choice. The middle portion of the photo shows the valve spring and spring keeper. The valves were ground in place relative to its stem using "Time Saver" fine grit, non-embedding lapping compound.
Lee allows one to choose between a 1/4" X 32 spark plug, or a much larger 10mm plug. While the 1/4" plug shown here looks very nice and is much closer to scale than a 10mm plug, it is far less forgiving than its larger cousin with regards to spark energy and fouling. The very simple answer, which I foolishly did not execute, and which Lee recommends, is the use of a steel bushing. The head itself is tapped for the 10mm plug, which may then be installed and used, giving one the advantage of a powerful plug, relatively immune to oil-fouling. Once the engine is running well, you could then install a steel bushing with an OD thread of 10mm, ID thread of 1/4" X 32, and enjoy the benefits of the pretty little scale plug. Two brands of 1/4" plug that I am aware of are the Rimfire brand and the Stits. The rimfire plug is the more common of the two. Either brand will set you back $15 U.S. each. Ouch.
The 10mm plugs, while not exactly common, are available via mail order from a number of suppliers, and the price is far less than 1/2 of the specialized 1/4" plugs. Be aware that the spark plug wires will have different terminations... if you swap plugs between the large and the small, you will also have to change the wires. Also, you've got to be careful that the spark doesn't jump from the wire to the nearby valve towers or valve inserts. If the plug(s) get fouled badly, the 35,000 volts needs to go somewhere, and the path I just described is what will happen. I know, I've seen it!
Photos: Front view of a completed cylinder head. A Stits 1/4-32 spark plug is installed, as are a pair of rocker boxes, also cast and machined. Rear view. The 2 ports (intake and exhaust) are barely visible inside the cavity milled into the rear portion. The fins were cut with a slitting saw on the vertical mill.
Like Lee's heads, mine are threaded to the cylinders. Threading almost guarantees a mechanically perfect interface, being strong and free of leaks. The only drawback is that the cylinder skirt holes must be drilled after the head is installed, as there is no way to predict the angular registration of the head vs. the cylinder.
Thus after roughly 10 months to a year, I started from nothing and ended up with a modest sand-casting outfit that would serve me well in the future, and 10 heads c/w valves. My goal was 12 heads, but the scrap-rate (that's machining scrap) knocked me down to 10.
Photo: A nice view of a cylinder head temporarily fitted to a "jug". The cylinder heads are threaded internally to match the cylinder, and a soft aluminum washer helps the seal. I plan on using high temperature loctite as well as a calculated interference fir to hold the head in place.
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