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Hoping someone on the Forum (perhaps @Gunrunner John) might be familiar with this based on actual experience.

I note that both Williams F3 and FA-1 diesels share the same motor truck - part number 293-E003. These engines have different motors however, with the F3 using part number 1468-E004 and the FA-1 using part number 808-E002. The only visible difference I can detect is the F3 motor carries a larger flywheel than the FA-1 motor. Presumably, the worm gear on both motors is identical as both use the same motor truck.

My question is this; since both motors use the same motor truck, would there be any issue with using FA-1 motors to power an F3 or, F3 motors to power an FA-1?

My purpose in asking is to make possible the upgrade of a favorite F3 to MTH PS3.0. This conversion is not possible with the F3 motor due to the size of the flywheel. The conversion is possible using FA-1 motors though. Since I have both models in my collection, swapping motors is an option provided there are no technical or mechanical reasons preventing it.

Thanks in advance for any info y’all can share!


Last edited by juniata guy
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I'm not Gunrunnerjohn but here are my thoughts: Yes you can use the FA1 motor if it makes it easier to mount the tach. But  I would swap both motors.  Since the flywheel on the F3 motor is a bit larger, it will store more energy.  So that motor will tend to start slower, and also try to coast a little further when power is cut, than the motor with the small flywheel.

Probably not enough to really matter, but if you want consistent starts with a minimum of "chuggle" they should both be the same.  My $.02.

Follow up to this topic in the event someone with the same question stumbles across it in the future.

The WBB F3 motors are 2” tall above the frame when fully seated in the motor truck. The inside dimensions of a WBB F3 car body are 2 1/4” wide and 2 1/8” high.

The WBB FA-1 motors are 2 1/4” tall above the frame when fully seated in the motor truck. Inside dimensions of a WBB FA-1 car body are 2 1/4” wide and 2 3/8” high.

The F3 motors would fit inside an FA-1 car body with no issue however, the slight height difference between the FA-1 motors and those of the F3, means the FA-1 motor is just a tad too tall to fit inside an F3 car body.

As the French would say - c’est la vie! 🤷


I wondered if the taller motor might be an issue.

I appreciate you mentioning it in your earlier response! To that point I had kind of just “eyeballed” the measurement. Your comment prompted me to actually measure and check the clearance before going further.

I’m disappointed it won’t work but, I reckon it’s always better to suffer the disappointment BEFORE spending money! 😉


The F3s have the skinnier flywheels but I am guessing they are too skinny for a wide enough tach tape. The question is if a flywheel thick enough for a suitable tach tape will fit. A custom machined flywheel would likely work if it was counterbored to fit over the bearing housing of the RS385. That would give an extra 1/8” or so.


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