Converting the Atlas O gauge Atlantic
to S Gauge

It makes a handsome S gauge Loco pulling a string of heavyweight passenger cars.

Click on images for larger view


The Atlas Industrial Rail Atlantic engine for some reason was scaled extremely close to 3/16" per foot , or S scale but was made on an O gauge chassis So this is my attempt at correcting it to be a S gauge loco that it should have been. It uses almost all of it's parts recycled from the junk box.
The basis for the conversion starts with an AC Gilbert Atlantic frame that has it's original front mounting bar cut off. 
Various bit and pieces are added such as a geared can motor, modified smoke unit, trimmed pilot truck, drive wheels from a late model Gilbert loco, valve gear and mounting brackets etc.  
The space is limited in the shell so power is limited to few choices. I went with my can motor conversion as it wouldn't need to remove the backhead of the shell to fit. A direct drive can motor could be made to fit by using a small motor. The sides of the chassis and motor plate  have to be narrowed to clear the shell. This required using four new number two screws used to mount the plate to the chassis.

A mounting bracket is made that fastens to the rear of the motor plate. I suggest you use the same screws that mount the motor plate to hold the bracket instead of the way I did it with the cap screws
The trailing truck is  recycled Gilbert from a late pacific. The draw bar is also from the same donor loco. The drawbar is bent and tongue cut down to mate with the Atlas tender drawbar. I re-used the Atlas truck screw.
The smoke unit requires some tweaking. The smoke tube needs to be relocated towards the rear to align with the shell smoke stack. Once  you can test fit the smoke unit in place with the chassis mark the new hole by using a drill bit down the stack that just fits in the stack hole.

I also made a smoke tube 3/16 longer than the Gilbert one. 

The smoke unit had 1/8" removed from the bottom of the mounting pads to make more room for the wiring in the shell. 
I chose to silence the smoke unit by removing the baffle and sealing the rear of sound camber. This increases the smoke too.
The old smoke tube holes are sealed in the cover and in the smoke unit casting with plugs made from slices of screws. Also a new smoke tube hole is drilled in the casting for filling the lower chamber with fluid. 

Smokes like crazy!
I made a bracket that holds the crosshead guide assembly to the chassis. It uses the same mounting holes as the chassis to shell bracket. They use 4-40 cap screws to hold the whole assembly together.
The connecting rod is Gilbert mated to the original Atlas piston crossheads
I opted to add a faux valve gear mechanism.
I made the valve hanger from pieces of 1/8" square brass stock. This required milling a slot in the chassis for the hanger.
The valve rod is pieced together with Gilbert bits and parts
The pilot truck has to have a slot cut into the crosshead guide assembly just like the Gilbert ones do. The pilot rivet and spring and washer are then assembled to the guide.
The pilot is truck shortened on one end to clear the drivers.
There is a clearance milled on the bottom sides of smoke unit cylinder to clear the tops of the driver flanges. Be careful not to mill through the cylinder wall.

The tender did not require much modification. 
I used American Models tender trucks.  The chuff switch is mounted on the coupler tang.

 Heat the heat shrink tubing on the chuff switch to soften it and bend to fit.
The speaker hole was added as well as the program/run switch.  The tender top is plastic so the TMCC antenna can be a piece of wire inside the shell.
I added 5/16" tall  fiber spacers to get the tender height correct. The coupler is an American Models passenger coupler that is shortened 1/4".  A new hole is drilled in the coupler shank for mounting to the bolster.
The original tender drawbar is slightly bent  as shown. The front truck fiber spacer has a groove cut in the top for the drawbar clearance. Pop rivets used as spacers are trimmed to size for free movement and countersunk for the flat head mounting screws for both trucks.
An ERR TMCC Beep Commander board was mounted with 1/4" plastic spacers to clear the  truck wiring below it. The ERR Sound Commander uses a mounting bracket made to clear the truck wiring below it. 
I replaced the original LED (yellow?) headlight  with a golden white LED and added a 2.2k dropping resistor The loco wiring has a connector for the headlight and the rear has the tether connector that fits through the existing hole in the loco shell.
It makes a decent looking loco that AC Gilbert would have liked

There are many ways to do this project.
One could go with more scale type wheels.
More details could be added to the front such as a scale coupler, handrails and clearance lights. 

You can use a conventional electronic reverse unit, DC or DCC if you prefer.

See what you can come up with.