Universal Parts Complete 50mm Big Bore Top End Kit for 50cc 4-stroke QMB139 engines.
Upgrades to 81.3cc based on a stock stroke of 41.4mm!
Includes cylinder, cylinder head, piston, pin, circlips, rings, head gasket, base gasket, HP Taiwanese camshaft, rocker arm shafts, rocker arms, cam holder, spark plug, intake studs, exhaust studs and exhaust gasket.

*You may need to modify your engine case to accommodate the larger cylinder.