Designing a racing piston that can take the abuse of high cylinder temperatures without melting down is a challenge the manufacturing wizards at JE Pistons take head-on, day in and day out. One concern which must be overcome in the piston development process is the amount of clearance between the piston’s skirt area and the engine block’s cylinder walls. This clearance has been the bane of piston designers for decades, as the piston’s proximity to the cylinder wall is crucial for a number of reasons – to prevent piston rock and reduce frictional losses. JE’s Perfect Skirt does exactly that.
“In order to achieve quiet operation and stable piston secondary motion, the piston to cylinder clearance should be optimized to provide the satisfactory minimum clearance when the engine is at operating temperature. At the same time, the clearance must be large enough to provide freedom from piston seizure under the intended operating conditions. To address these conflicting requirements, the clearance on a conventional non-coated piston is biased to provide freedom from seizure under any intended operating condition,” says JE’s Research and Development Manager, David Fussner.
JE’s’s newest venture into skirt coatings is known as Perfect Skirt, which, as the name implies, is a coating designed to provide the benefits of closing up the piston-to-wall clearance while also reducing operating friction, much like existing coatings. But it offers extended benefits as well.
“It’s formulated and applied in-house using a patented process on proprietary automated equipment, and then goes through a two-step thermal bonding and curing process,” says Fussner.
Traditional piston coatings have in the neighborhood of .0005-inch of buildup on the material surface; not so with the Perfect Skirt material.
“The coating thickness varies depending on the piston application it is applied to. The thickness is dictated by the amount of initial clearance that is being reduced with the application of the coating. Generally, the coating is at least twice the thickness of traditional coatings,” says Fussner.
Testing the product was a lengthy process that included many different applications on the in-house R&D dynamometer, along with thousands of actual road test miles to determine the proper formulation for the final product. The company subsequently filed a patent application for Perfect Skirt.
Unlike traditional coatings, the Perfect Skirt coating is designed to self-adapt to the specific cylinder bore in which it is installed. It’s designed to “buff off” only as needed until it develops the desired form. Basically, Perfect Skirt is bonded to the skirt surface and is designed to become the piston’s sliding area against the cylinder wall.
“The Perfect Skirt coating formulation has the unique ability to automatically precisely fit itself to the specific cylinder it is installed in. In the initial running of the engine, the piston coating in contact with the cylinder wall will adjust to its precise form quickly. The form at this time is the ideal automatically produced shape, at the automatically produced minimum clearance. At this point, the coating has settled into a uniform and equalized pattern, providing very low friction and quiet operation throughout its service life,” Fussner explains.
The piston will be designed by JE to fit the bore properly. The builder should choose the piston that is made to fit the bore size it is intended for, then install it, as the Perfect Skirt coating system does the rest by adapting itself into the bore and providing a forged piston with an excellent fit that will run quietly.
Perfect Skirt offers a way to keep your skirts perfect, crease-free, and sliding up and down with a minimum of muss and fuss.