The oil control check valve on all oil cooled Milwaukee Eight, also known as M-8 models regulates the amount of oil flowing to the oil cooler and cylinder heads. The stock assembly includes a formed steel check ball retainer. Over time, this retainer can fatigue and break, causing chips to flow through the oil system, back into the tank and can cause significant damage along the way. The S&S check valve is constructed of 6061 billet aluminum and the check ball retainer is machined from high strength steel for long lasting durability., guaranteed for the life of your motorcycle. Fits all oil cooled Milwaukee Eight engines 2017 to present.