Fitting Wheelsets

Wheelset The diagram shows the arrangement of the driving wheelsets. 2mm diameter axles match with the bearings supplied in the kits, and with the gears of driven axles. Unpowered axles can be of other diameters (requiring modification or substitution of the bearings supplied), e.g. the 3mm axles supplied in some conversion sets. For discussion on the possible choices of wheels and axles, see the Axle Bearings and Wheels and Axles sections of the Technical Description page on the website.

Pin-pointed ends should be removed from axles. If you are using ready-assembled wheelsets it will be necessary to remove at least one of the wheels from the axle.

Dismantle the Bachmann driven wheelsets. Recover the final drive gears and the axle bearings. Discard the wheels and axles.

The Bachmann axle bearings need to be opened out to accommodate differential movements of the axles in the suspension whilst at the same time holding the drive gears in mesh and transmitting the tractive forces from the drive train to the axles.

Open out the internal diameters of each of the Bachmann axle bearings from 2.0 to about 2.1 to 2.2 mm.

We found that the tapered end of a 2.3mm cutting broach was about 2.1mm diameter so used that to cut half way through the bearing from each side, finishing off with a smooth broach. Not a technique for the purist, perhaps, but adequate for our purpose. Alternatively, using a lathe, we have simply drilled through the bearings.

The following operations check the differential movement between the drive train and the bogie subframe. Repeat them for each bogie in turn.

Find the brass bogie subframe and bearing carriers for the bogie.

Axle with bearings Taking the new axles one at a time, and with regard to the identification marks on the bearing carriers and subframes, slide on to each axle a bearing carrier, two Bachmann axle bearings and the second bearing carrier. Note that the ears at the tops of the bearing carriers face outwards towards the ends of the axle.

Test fit wheelset in subframe Insert each axle into its slots in the Subframe, and check for free vertical sliding of the bearings in the slots, firstly with the axle horizontal, and again with the axle tilted such that one wheel is raised up to about 1mm above the other.

Orientate the brass Subframe and the Drive Unit. The 'four-wheeled' part of the drive unit goes towards the outer (i.e. coupling) end of the bogie, driving the centre and outer axles, with the socket for the cardan shaft facing the inner end of the bogie.

Test the fit of the drive unit within the envelope of the subframe, again both aligned with the subframe and also tilted slightly. Remove any remaining lumps or bumps from the drive moulding if these interfere with the movement.

Outer and centre axles in Drive Unit Take the centre and outer axles and clip them in to the drive unit using the Bachmann bearings.

Checking movement of outer and centre axles Fit the drive unit into the subframe, engaging the four bearing carriers into the slots in the subframe. Holding the drive unit with one hand and the subframe with the other, check that the drive unit can move freely up and down relative to the subframe with the carriers sliding in their slots. At rest the tops of the carriers will be level with the tops of the subframes. The suspension is designed to deflect ±0.5mm, so the free movement needs to be maintained both when the base of the drive unit is parallel with the base of the subframe, and when one axle is raised up to 1mm with respect to the other. If there is any binding when the units are parallel, check the movement of individual carriers in their slots and correct as necessary. If there is binding when one axle is raised, open out the Bachmann axle bearings just a fraction more, up to a maximum of 2.3mm.

Inner axle added If you are having three driven axles, remove the drive unit from the subframe and clip the third axle into place. Replace the drive unit in the subframe, now engaging all six of the bearing carriers into their slots.

Upward movement on inner axle Holding the 'four-wheeled' part of the drive unit such that the tops of all four of its bearing carriers are level with the top of the subframe sides, check that the third axle has at least ±0.5mm of vertical travel.

Downward movement of inner axle If this is not the case, check for free movement of the individual carriers in their slots and then, if required, open out the Bachmann bearings a little more, on this axle only, up to a maximum of 2.3mm.

That concludes the test. Unclip the axles from the Drive Unit and store them in their respective containers.

We now use one of the inner or 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 Bachmann 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), then a Bachmann drive bearing.

If it is a driven axle, slide one of the Bachmann final drive gears into position centrally. The gear should be a tight fit on to the axle, sufficient to transmit drive forces without slipping.

Slide the Bachmann bearings, then 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 inner and 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.