Bax, I had the same thing happen to my '54, 235. It was only noticeable while idling. It turned out to be a loose crankshaft pulley (harmonic balancer). Pull the v-belt back and fourth and if the pully moves, there's your problem. If so, you'll have to remove it and replace the woodruff key that keys it to the crankshaft and maybe the pulley itself. I hope that's all it is. Best regards, Jacques
