Are Williams F3 and FA-1 motors interchangeable?

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.

I agree with Ted, if they're using the same power truck, it's hard to believe that they won't work interchangeably.  Obviously, one might be taller than the other one, but that's about it.

Ted / Gunrunner; thank you both!!!

The plan would be to swap both current F3 motors to the FA-1 and both current FA-1 motors to the F3.

The FA’s have a large car body and should easily accommodate the larger flywheels on the F3 motors.

Again, thank you for your responses!

Curt

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! 🤷

Curt

I wondered if the taller motor might be an issue.

@gunrunnerjohn posted:

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! 😉

Curt

@gunrunnerjohn posted:

I wondered if the taller motor might be an issue.

Pretty sure the difference is flywheel thickness. Some might machine down the FA flywheel so it just clears the F3 shell.

Pete

I'd probably just yank the flywheel and use a skinnier one from my stockpile.  You might have to whack the shaft with a Dremel if the flywheel end was too long.

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.

Pete