Prepping Engine Cylinders – Cylinder Smoothing
There have been countless articles on the correct method of prepping engine cylinders for new (bigger) pistons during a rebuild or a custom build. However, there has been little published about the outside of the cylinders, the fins and the casting itself. Late model Evo and Twin Cam cylinders are aluminum and come out of the foundry/factory finished quite nice, a quick trip to the powdercoaters and they’re ready to run. The predecessors to the Evo (Shovels, Panheads, Knuckleheads and Iron Head Sportsters) all featured cast iron cylinders. These cylinders came from the molds with a fair amount of “flashing.” Flashing is a small amount of metal that seeps into the mold usually around the area of the cylinder where the mold was split (we’ll show you in the photos). Removing any errant flashing and smoothing the fins will make the cylinder look better once it’s powdercoated or painted and improves airflow around and between the fins.
We had a set of Panhead cylinders on the bench that belong to our friend Steve B’s custom Panhead chopper. The cylinders have already been bored and honed to fit the new pistons by Bob Bennett at Bennett’s Performance in Signal Hill, California. Now we will spend a couple hours smoothing out the castings using a number of files in different configurations and a Dremel tool with various accessories to get them ready for black powdercoat.