Heljan Class 52: Fitting Wheelsets

Six 2mm diameter plain-ended axles are required. Pin-pointed ends should be removed. If you are using ready-assembled wheelsets it will be necessary to remove one of the wheels from the axle.

For discussion on the possible choices of wheels, see the Wheels and Axles section of the Technical Description page on the website. Note that Ultrascale have, in their diesel disc range, Class 52 wheels matching the distinctive profile of the prototype.

We recommend that you arrange electrical pickup by using wheelsets that have electrical conductivity between the wheel treads and axles on one side of each bogie. This is sometimes known as 'American' style pickup. It avoids the need for separate wiper pickups and their associated wiring. Current flows through the components of the sprung bogies, which are insulated from the rest of the loco, with the connections to the loco's circuit board being made simply to the pivot screws holding the bogies in to the loco.

Shorting for Alan Gibson wheel To 'short' wheeltreads to axles, we have used this technique on Alan Gibson and Ultrascale wheels. Make a curled end on a length of phosphor bronze wire and solder it to the edge of one of the 2mm spacing washers supplied in the kit. Put a kink in the wire, shape it so that the the washer sits flat against the wheel boss (for the centre wheelset you might wish to thin the boss a little) and solder it (very carefully) to the inside of the (pre-tinned) inner wheel rim (make sure it's not fouling the running part of the rim). A slight misaligment will help maintain electrical contact between the axle and the washer.

Humphrys shorting disc, Gibson wheel Shorting Discs for Ultrascale wheels are available (to members only) from the Scalefour Society Stores, www.scalefour.org, and are written up by their designer, Mark Humphrys, in Model Railway Journal No. 248. We have used these successfully and can recommend them. An alternative design is available from Brassmasters, Ref A403 at www.brassmasters.co.uk/accessories.htm.

The photo shows one of Mark's shorting discs fitted to an Alan Gibson wheel. It's not quite big enough to reach the rim, even upside-down, so three short bridging lengths of PhB wire have been soldered in.

Ultrascale wheel, shimmed disc A disadvantage of the solid disc is that the connection with the axle can be lost as the hole in the disc becomes a looser fit on the axle as the wheels are removed and replaced. The flexibility of the Brassmasters type avoids that disadvantage (as it can be distorted slightly to ensure that at least one edge is bearing firmly against the axle), but the fixing to the wheel rim is more prone to failure. We have had some success with using thin shim of copper (from the sheathing of satellite coax cable) soldered across the hole in the solid disc, to be punched through when the axle is fitted. The shim can be replaced when necessary.

Removal of Undertray Spring off the lower cover from each drive unit. Remove the three wheelsets and replace the cover for now.

Use a relatively beefy screwdriver to unclip the four clips on one side of the lower cover, working from one end to the other. The cover may then be lifted away.

Dismantle the four outer wheelsets from the original loco, and recover the four final drive gears.

We now use one of the outer axles to check for lateral play. If you are using ready assembled wheelsets and have one wheel already fitted to each axle, you will need to vary the operations slightly to suit.

Taking one of the replacement outer axles, and with regard to the identification marks on the bearing carriers and subframes, slide two bearing carriers on to the axle. Note that the ears at the tops of the bearing carriers face inwards towards each other (this is the opposite way to most of the other PenBits kits).

Fit the wheels to the axle to the correct back-to-back measurement. Test fit the axle in the bogie subframe to determine the amount of lateral play. There should be just a little; enough to allow the wheelset to tilt such that the wheel on one side is raised about 1mm with respect to that on the other. If necessary, dismantle the wheelset and fit full- and half-width 2mm washers (supplied on the fret) between the bearing carriers and wheels, until this condition is met. If there is insufficient play, even with no washers fitted, reduce the inner width of the wheel bosses accordingly.

Record the washer configuration you arrived at and dismantle the wheelset. If you had to reduce the inner wheel bosses, repeat the operation on the remaining wheels.

Give some consideration to sideplay on the centre axle: in P4, with the clearance allowed for in the standard, a little Gauge Widening, and the relatively short wheelbase of the bogie, it may be that you do not have to allow any extra sideplay (theory suggests no more than +/- 0.3mm at 3' radius, even without those mitigating factors). If you are going on to fit the full brass brake detail, you do not want to allow too much sideplay here.

Now we can fit the Heljan gears to the new axles and assemble the wheelsets. Do the following for each axle.

If you have one wheel already fitted to the axle, slide on the required number of washers adjacent to that wheel, then the bearing carrier (ears facing inwards, away from the wheel).

Slide one of the Heljan final drive gears into position centrally on each driven axle. The gear should be a tight fit on to the axle, sufficient to transmit drive forces without slipping.

Slide the bearing carriers, then any washers required, on to the axle.

Fit the wheels to the axle to the correct back-to-back measurement. If you are using the 'American' pickup system make sure that the insulated wheel is adjacent to the carrier for the insulated side of the bogie.

Test fit each outer axle in its slot to confirm that the correct number of spacing washers has been fitted.

Lubricate the bearings with a light machine oil and ensure that the oil is taken in to all the axle-bearing interfaces.

That completes the assembly of the wheelsets.