Rotating a Pistion Joint

Perhaps my approach is incorrect, but I can't seem to get this to work.
I have a number of cubes falling from the sky. Once a collision is detected, and those cubes aren't connected, I connect cube b1 to cube b2 with a Pistion Joint. Eventually these cubes collide with the ground and I end up with a stack of cubes. Now, I want these cubes to also rotate around the upward facing axis (Y) 90 degrees once they're connected. So after I connect them with a Piston Joint, I also connect them with an Angular Motor Joint. But regardless of what values I plug in, I can't get any rotation at all. Thoughts? I don't want to connect them pre-collision... the idea is to be able to drop an unknown number of cubes from a starting point in the sky and have them connect on impact.

Thanks.

Having read your previous posts, I must admit, I can't exactly grasp what is it that you are trying to do. So far you seem to be using joints a bit too much. If you'll have too many of them - quite inevitable you'll end up having tweaking problems (such as with ragdolls). So, perhaps if you could supply a screen or something.
From what you've supplied so far - don't create another rotaion joint, there's no need, as you can simply supply the rotation data directly yourself.