Stage6 Streetrace 40mm 50cc cylinder kit for Vertical Minarelli scooter engines.
These were commonly found on early pre-bug type Yamaha Zuma, BW'S, MBK Booster, etc.
Very nice looking cast iron kit. Stage6 claims these are good for 7 or so horsepower when paired with a 17mm carburetor and sport touring type exhaust.
2 ring piston with stock style 10mm wrist pin.
Comes with cylinder, piston, rings, pin/clips, head, base gasket and o-ring for head.