Heljan Six-wheel (A1A) Drive Units: 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.

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

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 bearing carriers for the bogie.

Taking two of the replacement axles, and with regard to the identification marks on the bearing carriers and subframes, slide two bearing carriers on to each axle. Note that the ears at the tops of the bearing carriers face outwards towards the ends of the axle.

Slot the axles into place in the bogie subframe. Place the bogie subframe on a raised support so that the bearings can drop down to the bottoms of their slots.

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.

That concludes the operations to match the axle centres. Lift off the drive unit and return the axles to their respective containers.

We now use one of the outer axles, still with its bearing carriers fitted, 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.

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. Take off an extra 0.5mm on the wheels for the two centre axles, subject to not going beyond the line of the inner wheel rim.

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 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.