The piston kit for Harley Davidson Dyna models from 1999 to 2006 is made of a high-quality 4032 aluminum silicon alloy, which has a low expansion. The forged pistons are specially designed to be both light and robust. A accumulator between the first and second piston ring improves the sealing of the rings significantly. In addition, small grooves at the top of the piston minimize the risk of detonations. The piston surfaces are provided with an anti-friction coating in order to increase the durability and minimize friction.