Stay away from steel, they cause more problems than they are worth in my opinion, if you have the mesh set correctly then a spur will last a good while,When you mount the spur gear take a piece of paper and run between the gears, if you get a constant smooth "teeth" pattern your good to go, there shouldnt be any resistance when you spin the spur gear once the engine is remounted..... look up how to videos on youtube, they will clearly explain how to set your mesh.