Never...NEVER....hammer a cold harmonic balancer onto a crank. The way most of us old timers do it is to place the balancer in a pan of boiling water for 5-10 minutes. Quickly grab the hot balancer with your wife's best towel, duck her blows, and run out to the garage. Place it on the crank, place a 2X6 on the front pf the balancer and then hammer it on. Metal swells when hot and shrinks when it cools off. Trying to hammer on a cold balancer runs the risk of getting it 1/2 the way on and then not being able to move it.