Best Guess

Dear Greg,

Best guess via NWSL is 0.4mod for the teeth pitch. This is based on the NWSL site search bringing up an 0.4mod wormgear for Athearn (search term "Athearn worm").

Also worth considering that the classic "Blue Box" and newer "Horizon Hobbies" era trucks and gearing may exhibit detail differences? (We've all been caught out by that previously... :-(   )

Looking forward to seeing your TP56 build!

Happy Modelling, 

Aim to Improve, 

Prof Klyzlr 

PS for a DCC loco, mechanical flywheel may actually be counter-productive when teamed with some decoders (BEMF control VS Physical reality behaviour mismatch), and the flywheel mass of the motor itself is likely significant already, unless you're using a tiny 3.7V toothbrush/phone-vibrator motor or similar...

Best Guess Reply

I am taking your advise and elimination the flywheel. The motor for this critter is only about an inch long and a half an inch wide. This will leave me room for the speaker. 

I am planning on making these available on Etsy in kit form and am printing the first test print of the body as I am writing this.

You can follow the progress at ChippewaRailShops on facebook.

Cheers

Greg

You should be able to reuse

You should be able to reuse the existing worm and just change out the shaft.

Also, to reinforce the comments on not needing the flywheel.

The real purpose of the flywheels on a model locomotive is to smooth out the motor output. 3 pole straight wound motors such as Athearn used to use needed the flywheels to reduce the jerkiness of the motor. Skew Wound and/or 5 pole motors don't require this as much.

The flywheels, especially on a diesel are too small to effectively create a significant momentum effect.  

So use a 5 pole motor or similar and BEMF and you won't need flywheels at all. All they are is weight at that point.