Knock-out-pin type 125 motorcycle engine

The utility model relates to a push-rod type 125 petrol engine for motorbike which can improve the high speed performance of the engine and add the heat dissipation route of the piston, which comprises a brace, a connecting pole, a piston, a piston ring, a main shaft fifth gear, a countershaft fifth gear, a right crankcase and a cylinder. The utility model is characterized to that: the mass of the piston is less than 125g, the quality of the piston ring is less than 11.25g, the quality of the connecting pole is less than 3,650g, the ratio of the gear number of the countershaft fifth gear and the main shaft is not less than 1:1, at least one oil spit hole which is point to the bottom of the piston inner cavity is arranged at the right crankcase, the oil spit hole is communicated with the oil path of the right crankcase, the pressed height of the piston is 21.3mm, at least one oil hole which runs through the inner and outer wall is arranged at the skirt section of the piston, a continuous manger is arranged at the cover of the cylinder and corresponding to the oil spit hole.