Bachmann Class 66; Preparing the Locomotive

This section deals with the simple modification you need to make to the cast chassis block of the locomotive, namely, the fitting of pivot plates to provide surfaces against which to secure the bogie bolsters.

You will need to have completed the bolster and subframe assemblies before doing this work.

We assume that you are starting here with the loco dismantled: body separated from chassis and bogies and drive shafts removed.

Pivot Plates Remove the two Pivot Plate etches (P1) from the fret.

Fit of Pivot Plates in Chassis Block Invert the chassis block, and check the fit of the Pivot Plates over the bogie pivot holes, with their slots engaging in the cast transverse ribs either side of the holes.

Chassis Block prepared for plate Clear any raised features, oxidation, grease or loose material from the inside of the casting, in preparation for the glueing in of the Pivot Plates.

Fit of Insulator in Pivot Plate Check that the nylon insulators are a free fit through the holes in the Pivot Plates.

Pivot Plate and fixing screw. Prepare two 30thou plastic card spacers to fit between the top of each Bolster and its Pivot Plate. Each spacer should be drilled M2 for the pivot hole, and not extend beyond the perimeter of the Pivot Plate.

The plastic card spacers are to guard against the possibility of the chassis block sitting on the sides rather than the top of the Bolster.

Take the M2 pivot screws and two of the M2 Washers (A2) from the fret. Use these to secure a plastic card spacer, and Pivot Plate above, to the top of each Bolster. Ensure that the Plates are sitting flat and parallel with the Bolster tops.

Working Surfaces for Pivot Plate fitting Gather together a true, flat, hard, working surface, about 75mm (3") or more larger all round than the loco, and two true, flat, blocks of equal (about 6mm (1/4") or more) thickness and each large enough to take the footprint of the bolster.

Stand the bolsters on the flat surface and check that the top faces of the Pivot Plates are parallel to the surface. A slight deviation can be accommodated, any significant slope would indicate an error in assembly.

Arrange the Bolsters on the blocks, standing at approximately the correct pivot centres, and rest the loco over the bolster tops, adjusting their positions until the cast ribs, either side of the bogie pivot holes, engage in the slots in the Pivot Plates.

Loco sitting on Bolster Check that the chassis block is sitting level and upright. This can be difficult to judge, as the plastic chassis detail tends to 'droop' away from the chassis block at the ends. You may wish to refit the body to the chassis block and then make checks.

The loco in the photos sat true and vertical on the bolsters, but about 10thou (0.3mm) higher at one end than the other. A spacer of 40thou was substituted at the lower end before glueing the Pivot Plates. If you need to correct a 'lean' to one side, use a third support, under the fuel tanks, on the low side.

Having now established a relationship between the bolsters and the loco, the next stage is to glue the Pivot Plates into position. The glue acts both as an adhesive to retain the plates and as a filler to hold them at the correct spacing and alignment relative to the inside top surface of the chassis casting. You might wish to use a slow-set epoxy resin, to give plenty of working time.

Pivot Plate glued in place Carefully lift the loco off of the bolsters and any third support. Apply a protective ring of grease around the pivot screws at the top of each bolster, to prevent glue adhering firmly to them. Apply four or five spots of epoxy resin to the tops of the Pivot Plates on each bolster, each sufficient to form a 2-3mm diameter pad between the Pivot Plate and casting, but not so much as to squeeze out significantly beyond the edges of the plate. Carefully lower the loco back into place on to the bolster tops and any third support, ensuring that the casting ribs engage in the slots in the Pivot Plates, that the four 'feet' of each bolster are firmly in contact with the reference surface, and that the loco is supported in the previously established alignment.

Leave the assembly undisturbed until the glue has had time to set and gather strength.

Undo the M2 screws and remove the Bolsters from the Chassis Block, leaving the Pivot Plates now glued in.

If any excess glue has squeezed out around the Pivot Plates that would affect the rotation of the Bolster Top, remove it.