I know that this thread is a little old... But what do you mean by re-greasing the bottom bracket?I used a pk80 68.5cc slanthead engine on both of the cranbrooks. I'll be honest with you about this bike, Its not very durable stock. You should buy some HD wheels for it and really re-grease the bottom bracket before you motorize it. I also added a front hand brake to both of the cranbrooks I built but the guys who bought them love them and they haven't upgraded the wheels yet even though I advised them to. They are easy builds though.
Thanks