Bachmann 66: Springs, Bogie Assembly and Rolling Test

Primary Spring Wires Cut eight lengths of the primary spring wire, each 30mm long.

Degrease the wires and apply, to one end of each wire, a bead of fast setting epoxy resin about 1mm diameter, i.e. just large enough to prevent the springs being pulled through the holes in the ears of the central bearing carriers. Put the springs to one side while the resin sets.

Secondary spring wires Cut eight lengths of the secondary spring wire, each 18mm long. At one end of each wire, make a 90° bend 1.5mm from the end.

Primary springs in centre wheelset Return to the primary suspension wires and check that the epoxy resin beads have set hard.

Take four of the primary springs, one of the central wheelsets, and insert one spring through each of the four holes in the ears of the bearing carriers, feeding them through until retained by the epoxy beads.

Check that the epoxy beads do not restrict the movement of the springs in the carrier. Reduce their length and/or diameter if necessary (having only recently hardened, they will respond quite well to paring with a sharp knife).

Inner and outer wheelsets on primary springs Take the inner and outer wheelsets, check their correct orientation to the central wheelset, and slide their bearing carriers on to the primary springs.

Bogie wheeling jig Find a block of material long enough to support the bogie subframe, deep and narrow enough to allow the wheelsets to drop all the way down in their slots.

We use this tufnol jig for wheeling up and other assembly work. It allows the whole bogie to be turned round without disturbing any of the parts.

Wheelsets on subframe Place the bogie subframe on the jig. Pick up the three wheelsets together and rest them on top of the subframe, with the bearing carriers of the central axle aligned over their slots.

Pull the primary springs outwards so that their inner ends are sitting properly in the tops of the central bearing carriers.

Wheelsets in slots Move the inner and outer wheelsets towards the ends of the bogie, until their bearing carriers are engaged in their slots. Adjust the assembly so that the primary springs are sitting on top of the secondary spring seats.

Primary springs over secondary seats Using a small screwdriver to manipulate the springs, bend them outwards to slide over the secondary spring seats…

Primary springs over primary seats …and then down the outsides of the primary spring seats…

Primary springs seated … until they snap inwards and back up into their primary spring seats.

Turn the bogie round and repeat for the axle at the other end.

Assembled primary suspension You now have a rolling bogie with fully functioning equalized primary suspension. Do a hand-powered rolling test to check for any tight bearings, wobbly wheels etc. It is easiest to correct such things at this stage.

Fitting secondary spring wire Fit the secondary springs to the subframes: insert the plain end of each spring through the secondary seat adjacent to the spring retaining ear, then steer the plain end through the opposing seat, continuing to slide the spring through the seats until the bent-over end slips inside the retaining ear.

Secondary spring Secondary spring after fitting.

Fitting bolster Now take the bolster, make sure it is the right way round, and slide it into place over the subframe until the secondary spring seats of the bolster are resting on the secondary springs. Using a small screwdriver, push each spring slightly inwards while pushing the bolster gently downwards, so that the spring slides up the inner face of the seat and then snaps into the slot in the seat.

Bolster fitted Repeat the above operations for the other bogie so that you now have two rolling bogies.

Section Through Bogie Pivot The Bolsters are held in the chassis block by the M2 screws, nylon insulators and brass washers (P2, P3) provided in the kit. A plastic card spacer is fixed to the top of the Bolster, the thickness of the spacer being selected to produce the desired ride height for the loco.

The nylon insulator is shortened so that the screw can pull the Bolster Top up against the Pivot Plate, without the insulator touching the top of the Bolster.

The washer, P2, carries a soldering tag for the pickup wire for 'American' current collection.

Pivot Washers Remove the Pivot Washers (P2, P3) from the fret. Fold up the wiring tag on the edge of part P2.

Insulator fit in washers P3 Check that the main bodies of the nylon insulators supplied are a free fit through washers P3.

Spacers On a piece of 30thou plastic card, mark out two rectangles 8.5mm x 14mm. Find the centres of the rectangles and make a 3mm diameter hole at each, to clear the main body of the nylon insulators. Cut out the rectangles, and deburr their edges.

Fit the bogies - with their plastic card spacers - into the chassis block, using just the tag washers, P2, and the M2 screws. Swivel the bogies into position for straight track, and do up the M2 screws just enough to clamp the components closely together.

Refit the body, place the loco onto a piece of straight, level track and check the ride height. If necessary, substitute different thicknesses of plastic card spacer until the desired height is achieved.

Ride height is normally set to give a nominal buffer height of around 13.8mm above rail level. You may well find that there is a variation in the order of 0.5mm over the four buffers, just in the way that they've been fitted to the loco. You might also wish to check the maximum height overall, and then reflect on whether the manufacturer has got the buffers in the right place. Ultimately, working to tenths of millimetres, it will be a judgement call as to exactly where the correct ride height lies.

Once you are satisfied with the spacers, dismantle the loco once more. Remove the bogies from the chassis block, and remove the Bolsters from the Subframes. To remove the bolsters, gently pull them upwards, at the same time using a small screwdriver to push the springs inwards and out of their slots in the bolster seats.

Shortening insulator Shorten the nylon insulators so that, when inserted into the chassis block through the Pivot Washer, P3, they project below the Pivot Plate, P1, by less than the thickness of the plastic card spacer.

You can put the insulator over a 2 or 2.1mm drill, held in a pin chuck. This will prevent the insulator from collapsing while you roll it on the edge of a hard surface and make the cut with a sharp knife.

Bolster Pivot Screw Glue the plastic card spacers to the tops of the bolsters. Clamp them up against the Pivot Plate, using the M2 screws and all the other pivot components, as shown in the diagram above, while the glue sets.

Once the glue has set, mark the projecting threads of the pivot screws, remove and shorten them so they project no more than a thread's turn below the captive nuts.

Lightly coat the top of the bolster with silicone or multipurpose grease.

Refit the Bolsters to the Subframes.

Refit the Bogies to the chassis block and do up the pivot screws until there is just a very light preload between the Bolster top and Pivot Plate. You are aiming for a setting which allows the bogie to swivel freely, but prevents the Bolster from rocking against the Plate. You may well find that the screws slacken off as the bogies swivel: don't worry about that for now, in the final assembly they'll be retained by a thread locker.

You can now do static and rolling (pushed or pulled) tests to check ride height, body clearances, track-holding and suspension behaviour. It's helpful to clear any gremlins now, before the mechanical drives and detail are fitted. It is also extremely satisfying to feel how the locomotive moves with its sprung suspension.

You also have the option, at this stage, to do rolling tests with the Drive Units fitted to the axles (provided that you have not re-fitted the worms into the drives). Remove the bogies from the loco, and the Bolsters from the Subframes. Carefully place the Drive Units over the drive bearings on the axles, joggling the bearings into position as required, then push down on the Drive Units to clip them on to the bearings. Reassemble the loco and test as before.

You may not need to remove the wheelsets from the subframe at this stage, but, when you do, the procedure is as follows. Support the subframe on a narrow block as for fitting. Use the screwdriver to press one of the primary springs downwards and outwards, then lift that side of the end wheelset to bring the spring up on to the outside of its primary spring seat. Repeat for the other side, then lift the wheelset to slide the springs up over the outsides of the primary and secondary spring seats. Repeat for the axle at the other end of the bogie.