Lionel SD90MAC struggles to go backward

I seem to recall that I have had a motor loosen from it's mount.  All I needed to do was tighten the mounting screw.  

Is the motor mounting screw on this engine the screw in the center of the truck? If so, I made sure it was tight, but that made no difference. Also, when I removed that screw, I could not remove the motor.

Is there another screw or part that secures the motor on this engine? I've looked at the parts breakdown on Lionel's website (https://www.lionelsupport.com/...ON=productPartFilter), but I can't tell.

The one screw you are talking about holds the motor (Part # 10) and motor mount (Part # 23) to the truck (Part # 1), you will need to check part # 23 (Motor Mount) is attached to the engine with two screws (part #'s 40).

Those screws should be tight. The engine should not move any different in relation to the truck. If they are moving, even in the slightest, independent of each other, something is definitely loose.

Hope this helps!

Thanks!

Daniel is correct, the motor should be solidly attached to the truck.  The two different places that can come loose is just as he says, and I've seen both of those problems multiple times.

As I remember this bizarre truck design, you will have to remove the screw that holds the center rail power collector roller to initiate the dis-assembly of the motor/motor mounting plate.

Thank you, gentlemen. It was the two screws that attach the motor to the motor mount. One was barely in; the other was completely out.

Now I can't get the motor to drop all the way down into the gear box. What's the "trick" to getting it back in?

Try ever so slightly turning the flywheel while pushing down on the motor. 

romiller49 posted:

Try ever so slightly turning the flywheel while pushing down on the motor. 

Yup, turn the flywheel as you insert it back into the truck.

Before you do, this is also a great time to add/replace the grease in the gear box before you mate the two.

Glad the engine is going to be backing up into yards and sidings again!

As it turned out, my problem with getting the motor to drop all the way into the gear box was that I didn't have the bearings for the drive axle seated properly and the axle was sitting too high. Once I figured that out and got the bearings seated properly, the motor dropped right in.

The engine is back to running like a champ--forward and backward--even after 17 years of heavy use.

Thank you all for your help!

Happy endings are soooo much fun.