In the Mid-1980's I tried making Sn3 locomotives from HO mechanisms and was frustrated by their poor running characteristics. Athearn has reissued the HO Roundhouse locomotives and they run really well and can be converted into early narrow gauge locomotives found throughout the United States during the Golden Age of narrow gauge. Other tricks to make the old ones run great have been discovered.
The HO Roundhouse Mogul closely matches the Gary Caviglia plans in the March/April 1989 Narrow Gauge and Shortline Gazette. The stack and headlight are from IHC. We are using a 41" driver diameter.
Tomalco detail parts were available but are difficult to be found. The Pilot is a Selley part from Bowser trains, it is an oversize HO part but scales out to S.
(Click images to Enlarge)
Our narrowed mechanism on code 55 rail with ties we cut in 1986. We are using Bowser HO 56" drivers which are 41" in S.
The frame is narrowed to a width of .412. I used a small milling machine. The frame can be narrowed by hand with a large file. First cut grooves that are .044 deep at intervals along the frame. Then file down until the grooves disappear.
The front of the frame will be modified to take the new pilot.
The old Roundhouse frame used 1/8 inch diameter axles. The new ones use a smaller axle but can be easily modified to use 1/8 inch axles which are more prevalent. Romford in England makes drivers and catalogs an Sn3 axle. Bowser also has suitable drivers. The Alan Gibson workshop also has drivers.
Push the un-insulated drivers further onto the axle. Push the driver slightly beyond the check gauge cut off the axle and pull it back to the correct gauge.
The new HO Roundhouse locos pickup on all the drivers. Narrow the bottom plate assembly with a file. Locate the pickup strip a 1/64 away from the edge of the plate and drill holes through the pickup plate holder plate with a drill the diameter of the pickup strip. Drill holes through the bottom plate. Ream the holes in the pickup holder plate and press fit .047 plastic rod into them. Glue the rods. Increase the holes in the pickups and bottom plate for the rods. Relieve bottom plate for the pickups. Relieve the pickup strip around the gear slot.
A new PCB bottom plate with all wheel pickups can be added to the old frames.
Narrow the tender truck axles .044 per side. Push the wheels inward .044 and mount them on the trucks. A piece of plastic will be added to represent the journal box to close the gap between the wheel and side frame.
