This is my vintage Tomy train, I got it when I was a lot younger my guess is mid nineties, it stays at my mums house with all my old dark blue tomy track. I recently got a load if old track from eBay but had a real issue with this engine, it just wouldn't pull itself up hills and it struggled with rolling stock on the flat, so I took it apart to have a look, I also thought you'd like to inside one of these old locos with the reversing gearbox
Everything looked ok at first, but then I found this split gear, I repaired it with a little epoxy resin
With that repaired I regressed the gears and put the lid back on, I love this little loco, I was amazed at how easy it would be to to change the motor (although I wouldn't want to as I think you may strip the gears going from full speed forward to full speed reverse!)
Here's the gearbox with the motor removed, the motors only sandwiched between the two body parts, you can see the plastic selector under the motor which forces the directional switch 'full' forward or backward, if you look closely you can see the gear that the selector slides up and down the shaft, in one direction it drives the axle straight, in the other position it drives the counter rotation shaft behind the axle which then drives the axle, simple really
I've included an image of the underside if the top tray
You can see the switch mechanism and how it engages the drive the switch on the outside operates the long selector that engages the gear, in rest position the spring sits normally in the engaged position, when you turn it off it compresses the spring and disengages the motor side of the transmission
What I like about these, is that there is a blank fitted next to the battery, this can be removed so you can use x2aa batteries instead of just one,