As mentioned on the "What Did You Do On Your Layout Today" topic, the somewhat distressed 1225 Berk I picked up off of forum member Serge was a bit more distressed than I realized, as the gear train let go at Glitchcon. So, here's a look under the hood as I got the 1225 back up to snuff!
As a bonus, here's a RW in the shop for whistle contact cleaning (for the benefit of those who haven't seen RW guts before):
Disassembly of the 1225 is straightforward, with two screws under the cab and two under the steam cylinders. Here's the chassis sans boiler casting:
I did have to replace a broken ground wire going to the trailing truck. The contact and trailing truck need to be removed from the shell before taking it off.
Here's the underside with the roller pickup and bottom plate removed. Note the clever connection for track power (the brass captive nut). Also note the cam on the front axle for driving the smoke unit.
The old motor/worm gear and geared axle.
The top of the motor. Note that Lionel put two different flywheels for different versions of the 1225 onto the motor; be sure you have the right one before ordering a replacement!
The chassis with the motor and axle removed. Note the various indexing slots for the journal bearings.
Old and new motor and axle. Coming from a heritage of postwar Lionels that seem to last nearly forever, I find this amount of wear after ten years of use somewhat disheartening.
The new axle in place. It's easier to replace the axle, then install the motor and reconnect the side rods.
Disaster struck when one of the shoulder screws broke off in a wheel. I wound up having to reinstall the old axle temporarily, until I can get that screw removed:
With a temporary screw in place, the Berk was tested for a couple of laps sans shell.
While I waited for new shoulder screws and traction tires, I reinstalled the shell. The new screws and tires arrived Wednesday 8/12, and were duly installed. ProTip: You have to have the screws off the rods in order to install new tires. 
With new motor and traction tires, the 1225 was ready to hit the rails!
And here's an artist's conception of how it performed!
Hope this helps!
Mitch
