Bachmann K27 Reduction Gearbox

While testing a Bachmann K27 after installing R and K Railroad Products reduction gearbox, the third drive axle appeared locked in place. This caused the locomotive to teeter-totter on the third set of drive wheels. As this would probably reduce the tractive effort of the locomotive and encourage derailments, the locomotive was opened to investigate the cause of the problem.


The investigation revealed the installation of the R and K reduction gearbox had stopped the motor and gearbox from be able to pivot. The reduction gearbox moved the K7 motor rearward about 1 1/4 inches. This unfortunately caused the K27 fan to prevent the gearbox and motor from pivoting normally, and interfered with the suspension of the third drive axle to which the motor and Bachmann gearbox are attached. The impression in the Play-Doh shows the fan pressing on the new gearbox and limiting motion of the motor.


To eliminate the problem, the fan wires were unsoldered from the K27 printed circuit board, and the fan removed. But that only solved one of the problems. In the area behind the motor is a large printed circuit board with several sets of headers and multi-wire connectors. Now that the space for this myriad of heavy wires was cut in half by moving the motor back 1 1/4 inches, the wires were interfering with the movement of the motor and rubbing on the flywheel.


Although some K27 owners trimmed the mounting posts of the circuit board to resolve the problem, it appeared this would not provide enough clearance for the headers, connectors, and wires on the front of circuit board above the flywheel. Noticing that the motor was offset to one side, it was decided to mount the circuit board in the larger space on one side of the boiler.


The circuit board was fastened to the side of the boiler with hot glue. The wires on the front of the circuit board were pressed against the boiler and taped in place to insure they did not interfere with the flywheel or movement of the motor. All other wires were routed over the flickering firebox as the boiler was re-installed

After the locomotive was re-assembled, it was placed on a piece of track. All the wheels now sat squarely on the rails, and all four drive axles now moved freely on their suspension components. The teeter-tottering effect of the frozen third axle had been eliminated. This should improve the tractive effort of this fine locomotive.

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