My pal Tim has sent several 4-4-0s my way in the last few months, plus there was a 2-6-0 in the mix as well. All had bad axle gears, so I’ve had a bit of practice on the replacement of the gears. Today it took just 30 minutes - though Tim had removed the chassis for me so I didn’t have to worry about bodywork. He also bought the replacement axle gear from Bachmann, and he asked me to take photos so he could do the next one.
So here goes. Place on a towel upside down to protect everything. First the rods come off with a small socket or pliers (sockets do less damage if they slip!)
The wheel hub comes off with a small screwdriver, revealing the wheel attachment screw:
Finally, the bottom plate retains the wheel bearing blocks in the frame. The chuff trigger in the back makes it difficult to remove, so be gentle, and note that it won’t come all the way off.
So, with the wheels unscrewed and pulled off the axles and the rods removed, the bearings can be lifted out and laid at the side. Watch for the tiny springs underneath - you might remove them and safely store them as they are bound to fall out. (I used an old towel, so they didn’t fall very far.)
Now the motor is loose and will lift up out of the frame. Carefully slide the eccentrics and valve gear off the axle and wrap it with painters tape to keep it all together. Don’t move them too much - it is possible to let the piece that slides in the curved slot fall out when it is at one particular angle.
There are 6 screws on the gearbox - 2 at the back and 4 at the front. Carefully remove them and pry the gearbox apart over the axles, and admire the cracked/broken gear.
Insert the new axle instead of the old, and start reassembly in the reverse order. Be careful to
- make sure the springs are back under the axle bearing blocks,
- make sure the same axle block is on the side it came from (hence the suggestion you place them at the side of the frame. The wires on top collect power from the wheels.)
- jiggle the eccentrics (small black plastic disks) in the valve gear to make them fit snug against the gearbox. The circles in the ends of the valve rods go over the black disks.
- use loctite on the screws to make sure they stay in place. On this loco they were all a bit easy to remove.
Then ease the wheels back on, checking the rod pivots are aligned the same as the rear wheels so that the rods will fit. Keep screwing things together and you’ll be done in no time.
The final check is to apply power to the wheels or the contacts on top of the chassis to make sure that everything works as it should.