Big Bore Kit GY6 ATV Scooter Engine Motor 50cc to 80cc. 4 Stroke. CONDITION: BRAND NEW Change the size of your engine, and feel the POWER. Give your machine the new power and torque it really deserves, and have more fun with the power at your finger tips. 1x Cylinder Block. 1x Piston. 1x Complete Ring Set. 2x Circlips. 1x Piston Pin. 2x Head Gasket Set. Head Cylinder NOT INCLUDED. Size: Change from 50cc (39mm*41.1mm) to 80cc (47mm*53.2mm). Works with stock Cylinder head. Big Bore mostly fit: GY6 or GY6 engine clone (139qmb) Scooters. 50cc GY6 Go Kart engine. 50cc ATVs. 50cc Dune Buggies. 50cc Buggies. YERFDOG. SUNL. SYM. PGO. KYMCO. VENTO. STRADA. ROKETA. FUJI. WILDFIRE. KAZUMA.