This loco may look like it cannot be serviced, but it really can. I just fixed a balky 490 in preparation for selling it, and wanted to pass on the tips I learned as I went along, before forgetting them. This doesn't apply to those adventurous souls who want to take the whole motor apart, or to the double reduction motored locos.
The locos with the simple motor have no screws. The motor front is held by one clip, located near the front top of the motor, with two small tabs protruding from the engine's sides directly above the front drivers. Warm up both sides of the shell with a hair dryer (to prevent cracking), then pry the shell away from the tabs. If they don't release, heat a bit more and pry with a screwdriver with about a 3/16" blade. Slide the motor forward and out, holding a finger up against the front motor mounting clip. Note how the clip attaches, take a picture, or rubber-band it on for now.
Use cotton swabs and 91% isopropyl alcohol or your favorite grease-cutter through the conveniently-provided hole just above and to the right of the brushes, to clean the commutator. If you have one of those combination pencil & ink erasers that are encased in wood like a pencil, sharpen it so it fits in the hole, and polish the commutator face using the pencil end. Run a toothpick through the commutator's slots.
Lift the brush spring ends from the brushes with a miniature screwdriver. Turn the motor so the brushes face downward and rap it with your knuckles. They didn't fall out, did they? They're stuck in there with gunk. Find the slot on the side of the brush holders. Press the point of a push pin firmly against the brush and swipe down to dislodge the brushes. Clean the brush holders with swabs and alky. Clean the brushes in the usual way and determine if they need replacing.
Now, one of the most important parts: At each end of the motor are two copper strips about an inch long that are used for electrical contact. Clean the ends with a pencil eraser and alky. Also clean the tiny tab at the center of that front motor mount clip and the cab floor where those copper strips contact. All four surfaces should shine for good contact.
Reassembly will be easy if you have three hands. Remove the rubber band if you used one. Put a finger against the front motor mount clip. Move the drive wheels so the rods are in the far forward position, and slide them into the shell slots. Slide the rear securely into the cab floor, insuring that the copper contact is within the shell and touching the floor front. Likewise, the front contact should be behind the tiny center tab on the mount clip. Snap the motor front into the slots on the shell sides.
I wish I had photos to illustrate, but can't seem to get them to migrate from Picasa to this forum.
