These E7s are easily the best looking and best running of the 1970s Atlas/Roco diesels (although given the rest of the competition, that's not exactly a major achievement).
The all-metal chassis is quite hefty. The worm gear towers are actually attached to the trucks (as opposed to the chassis). I can't quite see the motor (what with it being buried inside the chassis), but I'm told that it's 5-pole / straight-wound. Long plastic driveshafts run from the motor to the worm gear towers (with plastic u-joints at either end). All gearing is plastic. Prior to 1980, all axles were geared. After 1980, only four of the six axles were geared. Eight of the twelve wheels provide pickup (the center wheels on each truck being electrically neutral). There are no traction tires. Current is transferred from the trucks to the PC board via wires (and from the PC board to the motor via flexible metal tabs). The couplers are truck-mounted Rapidos. A non-directional headlight is sandwiched between the PCB and the chassis. The wheel flanges are overly large, rendering these useless on Code-55 track.
As mentioned above, these are respectable runners. Throttle response is smooth, although performance at very slow speeds can be a bit uneven (probably due to the motor). I can creep mine through insulated frog turnouts without problem, so pickup is fine. Narrow radius curves are not a problem. Best of all, these are surprisingly quiet runners - easily the quietest Rocos I've yet encountered (the rest of them being a notoriously noisy bunch). In fact, if they'd gone with a higher quality motor these might just deserve an "A" rating. However, minor deficiencies aside, I'd still say they're good enough to operate (or at least they would be if there weren't other better options out there - IE, Life-Like, Broadway Ltd, et al).
Apart from the aforementioned gearing change, this model remained basically the same over its brief lifespan. It was ultimately discontinued circa 1982 when Atlas dropped their entire line of Roco-made locomotives in favor of their new line of Kato-made locos.
Circa 1985 Con-Cor started purchasing these shells from Roco and re-released the model with a new Kato mechanism (the same mechanism Con-Cor used under their E8's).
To remove the shell, simply spread the sides apart and lift it off.
Reviewed: 4/78 Railroad Model Craftsman (hey, send me a copy and I'll summarize it)
(Thanks for the mech pic, Rudolf!)