Small Engines (Lawn Mowers, etc.): engines, drive pulley, hp engine

Question
can you put a 6.25 hp engine in a old 12hp riding mower? will it have enough power to cut grass?

Answer
I wouldn't recommend doing this. First of all, the crank is probably not the right diameter or length to support the deck/drive pulley, and chances are, it will not have the power to run the unit properly. If it does, it most likely won't last very long.