S&S Cycle is an American motorcycle engine and parts engineer and manufacturer. S&S attracted controversy in 2005 when Harley-Davidson filed a patent and trademark infringement lawsuit against the company along with fellow aftermarket engine manufacturer Delkron, Inc. Harley accused S&S and Delkron of copying parts for Twin Cam engines and using Harley trademarks without permission. S&S argued that the suit was without any legal basis, and asserted that "a mutually beneficial relationship existed" between them and Harley. S&S Cycle develops performance replacement engines for V-twin motorcycles, most of which are replacement engines for Harley-Davidson models and are manufactured in the United States. S&S was the first motorcycle engine manufacturer to produce pre-certified United States Environmental Protection Agency compliant engines, lifting the burden and cost of performing the complicated EPA testing procedures from the companies and enthusiasts who buy S&S engines. The company also produces TÜV certified engines, and has even succeeded in complying with California's emissions requirements. S&S is the only motorcycle company in the world to manufacture Knucklehead, Shovelhead, Panhead, Evolution-style engines and Twin-cam style engines. S&S manufactures the largest (143 cu in (2,340 cc)) engine to fit a stock Harley-Davidson frame.