|LEGO® → System → Service Packs|
The motor is a single part, four studs across, and twelve long. It has three layers. The first is situated beneath the other two,is slightly skinnier and shorter, and has a hole into which a beam element can be placed. The next layer is longer and wider than the previous one, and has a 2X4 section jutting out at the far ends of the piece. The top layer is eight studs long, and is entirely stud-covered as well.