Harley engines, like Captain America’s “Panhead,” are named for the shape of their rocker boxes.
Since 1936, Harley-Davidson V-Twin engines have been named for the shape of the chrome rocker boxes that enclose their cylinder heads. “Knuckleheads” were replaced by “Panheads” and then by “Shovelheads” in 1966. The “Shovelhead” produced significantly more horsepower with significantly less engine displacement than current models. However, Harley was limited by government regulations as to how much power it could give to the engines and production was eventually halted in 1984. The heads were sand cast iron. A slightly smaller version was called the “Ironhead.” And, a standard way to make these engines even more powerful was to polish the interior of the heads and the intake and exhaust ports.
1. Remove the front and rear heads from the engine. Strip the heads of any movable parts including valves and seals.
2. Scrape the bottom of the heads with a gasket scraper and soak the heads in a 5-gallon metal bucket containing any degreasing solvent in a well-ventilated room for 6 hours.
3. Dry the heads with compressed air. Paint a 1/4-inch-wide line around the outside of the bottom of each head with black touch-up paint. Do not attempt to polish any part of either head that is not within that painted line.
4. Attach an abrasive roll to the shank of a rotary grinder according to the instructions for your grinder. Rolls usually attach to the grinder shank with a single, flat head screw. Work on one head at a time.
5. Lay one cylinder head bottom side down on a flat surface. Slowly grind the 90-degree edges of the intake and exhaust ports until those edges are no longer sharp to the touch, using a rotary grinder and abrasive roll.
6. Smooth the cast surfaces inside each port until those surfaces are shiny and smooth. Turn the head over.
7. Smooth the cast surface inside the hemispherical combustion chamber the same way you smoothed the interior of the intake and exhaust ports. Change abrasive rolls frequently. Do not attempt to physically change the shape of the combustion chamber. Do not polish within 1/2 inch of the valve seats, which are the clearly visible, machined area around the ports inside the head.
8. Install a polishing wheel on the rotary grinder shank using the same technique you used to install an abrasive roll. Polish the interior of the intake and exhaust ports and the interior of the combustion chamber using a rotary grinder, polishing wheel and polishing compound.
9. Repeat these procedures to port and polish the second head. Remove the touch-up paint from both heads with acetone and a shop rag.
10. Wipe all surfaces of both heads with new motor oil and shop rags to remove metal and polishing residue. Leave a thin coat of oil on the cast iron heads to prevent rusting until just before reassembly of the engine top end.
11. Wipe all surfaces on both heads with degreasing solvent and shop rags immediately before engine reassembly.