If I had to guess, the dogbone drive shaft. The chuffing indicates the flywheel and optical tachometer on the motor are spinning.
Cheap easy fix might be likely. PART 17 below
https://www.mthpartsandsales.c...lists/227?type=lists
EH1200002 | DOGBONE / DRIVE SHAFT / O GAUGE / 16mm L / ALT# EH-0000002 (Out of Stock) | 17 |
No fear, we go to alternate
In stock
EH0000002 | DOGBONE / DRIVE SHAFT / O GAUGE / 15.6mm L / PREMIER STEAM ENGINES | $3.00/ea |