Would it be possible to take two powered diesel locos that are to remain coupled back to back, both have one motor each, disconnect the E-unit from one, run a the motor wires from the E-less unit loco to the other locos E-unit and wire it such that when the one loco is running forward, it has the rear one running backward, and vice versa when you change directions? Can the E-unit handle the current of two motors?
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I've seen it done, but I personally believe the standard E-Unit is maxed out running one two-motored locomotive, and maybe more than maxed out! Those tiny contacts and cheap copper drums don't look like high current devices to me. 
@CALNNC posted:Can the E-unit handle the current of two motors?
Go for it. Lionel used the 3 position mechanical e-unit with all of their dual motored locomotives!
I don't know if the contact fingers and drum segments are universal across all Lionel E units, or whether Lionel used different units depending upon application (1-motor locomotive vs 2-motor). It would seem from a quick thought process that if an E unit in a 2-motor unit is robust enough for 2 motors, then installing that same E unit in a single-motor unit, and MU'ing the contacts to a second, single motor unit, it would work OK.
You could, of course, convert the E unit to an electronic one, perhaps from Dallee or a similar company. The manufacturer would be able to tell you the current-handling capacity of their product, and you could measure the start current of your two motors to ensure success.
@Arthur P. Bloom, the contacts and fingers are all the same across the e-units. The drum is always a 259E-1 and the fingers are all the same construction with different part number assigned per wire length arrangement, but standardized 100-45 and 100-46:
I’ve seen it done. While your at it, it’s also a good idea to run a wire from the roller pickups on the trailing unit to the solder lug on the e-unit in the lead engine. If you’re running three wires between engines you may as well run four and improve the performance. I especially recommend this if you are connecting MPC-era engines together.
As far as overload on the contact points on the e-unit, if you try to daisy-chain dual motored engines together the amperage could become too much for the contacts to handle. E-unit drums will heat up and melt on occasion.
Yup, 4 motors on a e-unit drum is a recipe for a funky stink!
E-Units were engineered for 4 motors.
Your MU scheme is solid... you can tether both motors to one e-unit, even while leaving reverse units in both cabs. Here is the diagram for doing so(the connection between cabs is circled in green, use your choice of connector). If you leave the slave unit locked in neutral, it can be restored to operation by unplugging from the master and turning the E-unit back on.
Thank for all the input on this subject, and the schematic. Now to work.
"E-Units were engineered for 4 motors."
How do we know that? is there a real-life application where four motors re controlled by one E unit? Or are you estimating by observing the size of the contacts?
A firmware update for the EEU described in the April/May 2019 issue of O-Gauge Railroading (#305) allows two locomotives to maintain synchronization when running in tandem. The update is available for a nominal charge, most of which is postage.
@Arthur P. Bloom posted:How do we know that?
@KRM posted:it is my understanding a Lionel E-unit can run 4 pulmore motors. I see it everyday with my 4 motor A-B- A ALCO unit. But it is a bit much for the transformer. I think the better option is three motors.
Not sure where @KRM came up with his knowledge, but this is just something I've been aware of for 45-50 years... maybe from Frank Kanzler or Earl Gardner?
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