The Energon Pub

first transform him to robot mode. grab the little panel that sticks up behind his head and pull it all the way forward, as if you were closing the hood of your car- do not let the automorph feature activate, you should be able to move the head panel thing without the automorph, similar to the sword on voyager megs cannon. I used my fingernail to hold the gears on his chest in place but this may not even be necessary.

now flip the head panel back to its normal position this time pressing down on the head as if you were going to snap it into place.

repeat these steps, flipping back and forth, until the head panel is no longer "floating" a scale foot above bumblebee's chest.

worked with mine, hope it works with yours too