I pray that You smeared, the spring side of the front crank shaft seal, liberally with some good grease. It is not uncommon for the spring to pop out of the seal when driving it into position onto the front cover.
A light and a mirror will tell the story, the spring will be dangling around the cranking shaft.
Uh Oh! I did smear the spring side with oil before getting it in place. I'm not sure id use the word liberally, though.. When I looked at it, it looked fine, and I started the engine after I had the new balancer In place and everything seemd fine. But I guess time will tell..