1985 mustang 302 50 oz balancer and flywheel.Car started to appear to have a miss and vibration right off idle.Check all the normal things then with the timing light notice timing was way off.Rubber on balancer looked good,but I took the crank pulley off and i could feel the the balancer had play in it as a I spun the crank pulley.Pulled the balancer and the woodruff key had elongated the slot on the balancer to about 3/4 of an inch.The balancer bolt was snug but seemed like it back off some from where i had it when the motor was put together.I think this let the balancer move enough to start chopping away at the key channel on the balancer.Put a new balancer on it and made dam sure that bolt was tight.Car runs fine again,But that was my Sunday adventure.