Heljan Class 35: Springs, Bogie Assembly and Rolling Test

Spring wire sizes are listed on the card inserts that come with the kits.

Spring wires Take each of the four lengths of primary spring wire and make a 90° bend, approximately 3mm from one end, in each wire. Trim the long length of the wire to 68.0±0.5mm

Cut four lengths of the secondary spring wire, each 23mm long. Make a 90° bend in each wire, 2mm from one end.

Subframe with wheelsets slotted in Take one of the bogie subframes and slot its two wheelsets into place.

Route of Primary Spring Wire Route of Spring Wire through Carrier Take one of the primary spring wires, and thread it into place as shown in the diagrams here. It passes through first the inner stretcher, then the carrier for the inner axle, then the central spring seat, then the carrier for the outer axle, then the outer stretcher.

If the wire will not pass freely through a carrier, use a 0.5mm drill to clear any excess solder from between the bearing and the carrier etch.

Primary spring retention Spring the short end of the wire into the retaining clips on the inner stretcher. A small flat-bladed screwdriver can be used to steer the wire around the clips.

Fitting second primary spring Similarly fit the primary spring on the other side of the bogie.

Similarly fit wheelsets and primary springs to the second bogie. You now have two rolling bogies 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.

The chassis should be free-running - the wheels should turn easily under the self-weight of the bolster and subframe when pulled along track. If a wheelset is sticky check bearing alignment, BB measurement and verticality of subframe sides. Pay attention to the path of the spring through each bearing carrier: a small obstruction can twist the bearing, insufficient lateral play can pull the spring inwards.

Bolster and secondary springs Now take the bolster assemblies and pair them up with their respective bogie subframes.

Pass a pair of the secondary springs through the holes in each side of the bolster. Retain them in position with short lengths of wire insulation, as shown.

Positioning bolster in subframe Slide the bolster vertically into position over the traction ears between the inside faces of the subframe, at the same time clipping the secondary springs into place in their seats.

Here the secondary springs are shown resting on their seats…

Fully assembled etched components …and here are clipped into their seats.

Similarly fit the other bolster to its bogie.

Section through Bogie Pivot The bolsters are secured into the pivot frames using the M2 screws and nylon insulators 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 clamp the pivot frame, spacer and bolster up together without the insulator touching the top of the bolster.

The brass washer (4) can be omitted. It is useful as a soldering tag for the pickup wire if using 'American' current collection.

Spacers On a piece of 30thou plastic card, mark out two rectangles 7mm x 14mm. Find the centres of the rectangles and drill a 3mm diameter hole at each, to clear the main body of the nylon insulators. Cut out the rectangles, and deburr their edges.

Shortening insulators Shorten the nylon insulators so that the unflanged part is about 0.5 - 0.7mm long.

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.

With the Pivot Frames fitted into the loco chassis block, fit the bogies - with their plastic spacers - into the frames, assembling the pivot components as shown in the diagram above. Swivel the bogies into position for straight track, and do up the M2 screws sufficiently to clamp the components fairly firmly together.

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 put the body back on to the loco and check for 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.

Assembled bogie with spacer Once you are satisfied with the spacers, glue them to the tops of the bolsters. Clamp them up against the pivot frames, using the M2 screws, 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 pivot screws and do them up until there is just a very light preload between the bolster top and pivot frame. You are aiming for a setting which allows the bogie to swivel freely, but prevents the bolster from rocking in the frame. 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 are fitted. It is also extremely satisfying to feel how the locomotive moves with its sprung suspension.