Montesa 4rt S3 300cc Big Bore KitKIT CYLINDER PISTON BIG BORE FOR MONTESA HRC 300cc 4RT. High quality product. More capacity gives the engine more torque on bottom and more power on revs. The engine is very smooth on low RPM, and very powerful on high RPM. Engineering and production 100% made by S3. Heavy duty casting, with more water capacity and more water circulation, flux spiral. The kits are delivered ready to fit on the engine, with cylinder and piston already assembled, and