I checked my supply of about 30 different Lionel motors, and the Lionmaster Challenger motor I have is way thicker shaft. I was surprised - thought they'd be the same. Seems the other Lionmaster Big Boy's used a different one than this one as well. Ouch - I have the same engine - hope it doesn't develop the issue. I have a 11 year old that thinks he isn't pull 30+ cars its boring.
Let us know how it turns out.
Jim