Modifying the Heljan Bogie Drive

Unplug the cosmetic sideframes from the two mounting studs on each side of the drive unit.

Top cover Cut the pivot hole tag from the top cover of the drive unit to leave the top flush. Chamfer the top rear edge of the cover. Refit the cover to the drive unit.

Spring off the lower cover from the drive unit.

Coupler pocket Separate the two halves of the drive unit slightly and remove the coupler pocket. Cut off the mounting eye and forked spring mouldings associated with the coupler.

Remove the projection from the rear of the drive unit which would support the moulded brake gear.

Axle spacer mouldings Reduce the depth of the arched shaped spacer mouldings around the end axle holes of the drive unit. The overall width should be no greater than about 10.5mm.

Sideframe mounts Remove the pickup contact strips from the sideframe support studs and then trim back the studs to leave about 1 - 1.5mm projecting from the drive unit.

Undertray Remove the moulded bumps from the lower surface of the lower cover; in many cases they can be taken down flush without making a hole in the moulding, but it does not matter too much either way.

Take a little of the thickness off the outer ends of the lower cover moulding.

Modified drive unit Enlarge the central axle slot to give at least 1mm clearance around the central axle.

The following operations match the axle centres of the drive unit and the etched bogie subframe. Repeat them for each bogie in turn.

Find the brass bogie subframe and wheelsets for the bogie, which should still be all assembled following the first rolling test.

Orientate the bogie subframe and the Heljan drive unit, with the socket for the cardan shaft facing the inner end of the bogie.

Place the drive unit over the axles so that the axles engage in the slots in the drive unit. If the drive unit does not fit freely on to the axles, relieve very slightly the inner or outer faces of the slots in the drive unit until a free fit is achieved. Free vertical movement on the axles should be maintained when one end of the drive unit is raised about 1mm above the other. Check also that the drive unit is free to pitch and roll within the subframe, taking off any further material as necessary.

That concludes the operations to match the axle centres.

Drive Unit in situ This photo shows how the modified drive unit fits into the subframe and bolster assemblies.