This counter balance shaft is a genuine replacement part for Chevy and GMC 4.3L Vortec mercruiser engines with timing gear. The part number is 3857715 and it is designed to maintain engine balance and reduce vibration for a smoother operation. Made by Volvo Penta, a trusted brand in the marine industry, this internal engine part is a crucial component for any boat owner or mechanic. Whether you're replacing a worn out part or performing an engine rebuild, this counter balance shaft is a reliable choice that will ensure your boat runs smoothly and efficiently.