B units?

I don't think any postwar B units were powered but some made after 2000 I think have motors in the B unit.

After the release of the E8s, 3rd Rail no longer does any non-powered units.  They can be synced in conventional with careful use of the throttle or synced using command control.  Personally, I do not like non-powered units and only use them when I have at least two powered units for my largest trains.

K-Line did their F3s with motors to all the axles with a tether.  The E8s were also done this way.  Early MTH E and F units also used a tether to connect A and B units.  I can't speak to Lionel as I do not have any Lionel diesels.

All of mine are powered.

In the late 1990s Lionel produced F3 B (and trailing A) units that were unpowered. An unfortunate idea, my ABA units struggle to run light...  I use the B units as HEP on occasion.

Jan

A B unit from the 1990s...

I had an FA-FB unit that ran in conventional in sync. Presently my powered units are tethered and are controlled by the A unit so that in conventional they stay on the same page. Bs that I want to swap between locos I leave unpowered.

K-line had powered aba but these had in truck motors with no tmcc. Still nice and they run flawlessly. I have all the different road names they offered in my collection and I like them alot.

Atlas produced some powered F-3 B units.  (I had one; I’ve since sold it).

All the manufacturers have powered and unpowered B units, along with powered and unpowered A units.  I have had fairly decent success running powered units together where they don't fight each other.

Atlas unpowered units are heavier, in my experience creating pulling power issues.  

If running a F unit (F3/F7) or E unit (E8), I almost always want a second engine for aesthetic purposes, single units don't look right (to me).

John