Compatibility between motors and trucks of different models/manufacturers?

Chances are good that motors from the same MFG have the same gearing teeth. Swapping motors between different mfg's will NOT have the same gearing teath.

SO Williams with Williams, WBB with WBB- [I am NOT sure of early Williams to WBB]

Weaver to Weaver, MTH to MTH, etc.

NO Weaver to Williams- the Motor Key for Chassis and gearing are OFF.

If you are trying to swap out two Williams motors and truck assemblies it should work as long as they are very similar. But if you are trying to swap Williams and Weaver or MTH it may not work. With Williams engines the couplers are mounted to the truck assemblies.

First see if the truck assemblies are about the same length, if not you might be able to swap shells rather then truck assemblies by drilling new mounting holes in the metal frame. 

Lee Fritz

Sam, it would probably be just as easy or easier to install ERR CC/RS as it would be

to swap things, even intra-brand. The price is not stupid, it really is easy to do - especially on diesels with no "chuff-switch" to install and typically plastic bodies.

And you would have another powered loco.

Actually, several years ago I picked up an early RK Dash 9 PS2 for about $100. Not being particularly mechanical or handy, I decided to pull the electronics complete with the motors (and the attached tach strip) and swap them with the electronics in our Williams E7s. Surprisingly, everything dumped right in place. Both engines fired right up and ran well. I was happy that I had upgraded my Williams L&N's for essentially nothing ( I resold the RK Dash9 at auction with the conventional E unit and True Sounds for $100) and they ran reasonably well. 

Not perfect as I later discovered that when subject to a real load, the engine will make a 'pop' sound which I surmise it the gears 'jumping' a notch. Otherwise they still operate fairly smoothly these three years later.

It is amazing what sometimes fits - a motor with its gears, etc., from my spare parts box taken from an MTH ten years ago into a year-old WBB trainmaster that burned one of its motors.  For some reason that trainmaster burned up two motors and it now has motors from an old MTH loco about ten years or more ago. 

And there there is this, which I hoped would work, but could not believe actually did!  I took two axles out of the old K-Line/K-Line by Lionel 'Streets shorty school bus, and they slipped into the truck of the new WBB 440-tonner, replacing the axles and wheels that came with it.  Maybe not a surprise, except you fit an axle into that truck by fitting its bearings (small square sintered bearings permanently attached to the axle) into slots molding into each side of the truck's chassis, these they fit!  ten years apart, one a 'Streets product, one a loco, K-Line to WBB.  Proof it pays to always try.  (This is for a 'Streets bashing project and when its done I will post pictures.  Pretty cool so far!)

I was surprised the MTH trucks from a premier GP 35 2 rail fit in this atlas gp35 hi nose which now is all ps3.

Front truck is scale fixed.. rear is floating with a DCS command electro coupler. Sweet running switcher

The Williams F-3 has a lower body height than the other Williams wagon top diesels. The flywheels in the F-3 are low/thin and large diameter, like a pizza. The flywheels on other Williams diesels are tall and their diameter matches the motor, like a tuna fish can.

So, you cannot put other Williams motors into an F-3. You can put F-3 motors into an FA-1, but not the other war around.