Conversion of Intermountain 40' box car
Intermountain's 40' box cars are built with an injection-moulded plastic underframe on which trucks with couplers are mounted, and an injection-moulded plastic body glued to the underframe. The cars are delivered with low-profile plastic wheel sets of lesser quality than that of Micro-Trains, and truck-mounted couplers. These older cars have couplers that cannot couple automatically.
The cars are designed so that the height from rail top to the coupler mounting platform is approximately 7.4mm. There are holes in the floor that fit the Micro-Trains #1015 and #1023 couplers. I don't like the #1023 coupler as the coupler spring is in compression when the car is hauled, this can lead to the cars bouncing back and forth in a long train.
I like to use wheel sets with small flanges and #1015 couplers. This type of coupler is designed to be used without a shim for a mounting platform height of 7.1mm above rail top and 7.4mm with a shim.
Photo 1: Here the car is seen as delivered with plastic wheel sets and non-functional truck-mounted couplers. The truck bolster pin is pressed into a hole in the underframe bolster.
Photo 2: The trucks are removed from the underframe by prying out the bolster pins, and the wheel sets are removed. On one truck the coupler is cut off using a jeweler's saw and the cut cleaned up with a sharp knife. Be careful that enough material remains around the truck bolster hole.
Photo 3: The wheel sets are remounted in the trucks; a bolster pin is seen to the left. An assembled Micro-Trains #1015 coupler and 00-90 mounting screw are seen to the right.
Photo 4: Here the trucks are remounted and the car is placed on the track next to a Micro-Trains Coupler Height Gauge. The height of the coupler mounting platform is approximately 7.4mm above rail top, i. e. approximately 0.3mm too high for #1015 couplers without shim (I prefer not to use shims). The height is corrected by filing 0.3mm off the truck bearing surfaces on the body bolster.
Photo 5: The car is fastened in an engineer's vice; to spare the car sides soft liners from plastic, card or leather are used. The doors should be dismounted before. The truck bearing surfaces are filed and mounting holes for the new couplers are tapped with a Micro-Trains 00-90 tap (can only be used for tapping plastic).
Photo 6: The new #1015 couplers are mounted and the trucks are remounted after the changes have been made. On this car I later mounted Intermountain 33' metal wheel sets with RP25-flanges as it did not roll well enough with the plastic wheel sets. Other similar cars have retained their original wheel sets.