REPOWERING

The Pacific Fast Mail

Class B 2 Truck Shay

Brass HO scale two truck Class B Shay, imported by Pacifc Fast Mail, built in Japan by United.  PFM Shay models are among the most popular HO brass steam models, even though most were imported with solid brass wheels and a relatively crude gearbox.  With addition of a new flat can motor and flywheel these models run even better and a bearing can be added to the gearbox to improve and stabilize gear mesh.   Details on how I did it below.

As would be expected with a Geared locomotive, this model's mechanism has a lot of gears.  All the axles are driven from gears on the right side of the engine; a center gear tower powers the side drive shaft thru gears hidden behind the cylinders.  A large Pittman motor provided dependable power and also provided alignment for the upper gears.  Misalignment of these upper gears can lead to poor running, premature gear wear and ultimately an inoperative model.  The photos below show the mechanism and the upper gear alignment I found in a used model.

Not all of these hand-assembled gearboxes are exactly the same.  Slight variations in assembly angles can mean that the upper gear on the motor shaft cannot be properly aligned and keep the motor inside the space available.   Note how the stock motor is as wide as the engine frame in the photo below.  This is also a problem in other PFM geared models.  Better gearbox designs provide bearings for alignment of all the gear shafts as part of the gearbox, especially the critical upper worm shaft.  Adding a second bearing on the upper worm shaft will allow improved alignment of the gears independent of the motor shaft. A short universal drive will be used to connect the motor and gearbox.  Replacing the large Pittman motor with a more modern flat can motor will also allow the use of a flywheel to provide smoother running qualities.

The motor shaft on this model is 2.4mm, a common size on Japanese models.  NorthWest Short Line (NWSL) among others have made 2.4mm  hat bearings available that can be used to support the front end of the worm shaft.  To create the front bearing support I used K&S square tubing, rectangular tubing can also be used.  For a foundation for the bearing support I soldered K&S 1/4" angle stock to the vertical post.  The angle stock can be held to the frame by screws or soldered, your choice.  I drilled a slightly oversized hole for the bearing in the vertical post.  I mounted the worm on a piece of 2.4mm shaft stock (NWSL) and positioned it for good alignment and used the shaft end to mark the vertical post for the bearing hole.    I drilled a slightly oversized hole for the bearing, this will allow some final adjustment before soldering the bearing to the post. 

Be sure to add thrust washers in the gearbox to eliminate end to end play in the worm shaft.

I have used several flat can motors in PFM geared models.  Many years ago I was using Canon CN2231 motors,  then I switched to the Kato motor used in their HO diesels.  This model  has the motor secured to the frame with a phosphor bronze strap soldered to a K&S angle; on the other side the strap is tightened to the angle piece with a screw.  Both angles pieces are soldered to the frame.  On other models I mounted the motor  with 5 minute epoxy on a flat brass plate (see Climax guide).  The flat brass plate is held to the frame with screws.  Both methods allow easy removal of the motor.  A small flywheel is mounted on the worm shaft extending out the rear of the gearbox.  A short Hobbytown universal drive completes the drive train.