Bachmann 66: Final Assembly

If you already have the three axles and their springs fitted into the Subframe and, possibly, even fitted in to the Drive Unit, try to retain that as far as possible to avoid more dismantling and reassembly than is necessary (allowing you to skip over some of the following instructions).

Replacing the Worm Drives

Adjusting worm - bearing spacing Place the worm shaft and its bearings into position in each Drive Unit. Ensure that there is a little 'end float' between the bearings and the worm.

Worm cover with bearing seats relieved Refit the plastic worm covers. Check that the worms rotate freely with no tight spots: diagnostic for this is also that the shafts move freely fore-and-aft over the axial 'end float' referred to above. If the shafts are tight (they were pretty much immovable in our test build: the covers seem to sit differently now we have removed the pivot part of the moulding) the solution is to relieve the semicircular bearing retaining surfaces of the top cover, using a round file.

To check that the worm shafts are absolutely free, it may be advisable to dismantle the wheelsets from the Drive Unit.

Lubricate, sparingly, the teeth of all gears in the drive train using a suitable grease. Lubricate the worm shaft bearings with a light oil.

Assembling the Bogies

Take one of the Drive Units and fit its wheelsets, ensuring that they are in the correct locations and the correct way round, as indicated by the id marks on the bearing carriers. While doing this, adjust any pickups to give a light preload onto the wheels.

Inserting primary springs Using a pair of tweezers to handle the springs, and a small screwdriver to manipulate the bearing carriers, thread one of the primary springs through the hole in one of the ears of the central bearing carrier.

Thread the spring through the slots in the ears of the bearing carrier of the opposing axle.

Thread a second spring through the hole in the other ear of the central bearing carrier.

Second primary spring Thread that spring through the slots in the ears of the bearing carrier of the remaining axle.

Similarly fit the two springs on the other side of the bogie.

Subframe on wheeling block Take the Subframe which goes with the Drive Unit and place it on the narrow block for wheeling.

Orientate the Drive Unit correctly with the Subframe.

Drive unit introduced to bogie Slot the Drive Unit into the subframe with the primary springs resting on the tops of the secondary spring seats. Ensure that the bearing carriers are correctly engaged in the slots in the subframe.

Primary springs over secondary spring seats Push the primary springs down to slide them outside the secondary spring seats.

Primary springs outside primary seats Use a screwdriver to push the primary springs outwards and downwards on to the outer faces of their own seats.

Clipping primary springs... Push the springs downwards so that they slide over their seats…

...into place …until they snap inwards under the seats and spring back up into place.

Fitting bolster Now take the Bolster for that Subframe, make sure it is facing the right way, and slide it into place in the Subframe, until the lower edges of the four secondary spring seats are resting on the secondary spring wires.

Pushing down gently on the Bolster, use a small screwdriver to bend each spring slightly inwards so that it slides up the inner face of its spring seat and snaps into the slot in the seat.

Assembled bogie Repeat for the assembly of the second bogie.

Checking Clearance over Worm Cover

Place the bogies on a level surface and lower the chassis block onto them, adjusting the position of the bogies to line up the pivot holes.

Push down on the chassis block, at each end in turn, to compress the suspension about 1 to 1.5mm. This is more than will normally occur in operation but, if the vertical movement is restricted, to less than say about 0.75mm, by the chassis block coming to rest on the tops of the worm covers, you might wish to substitute the plastic worm covers by the etched covers supplied in the kit.

Fitting Etched Worm Cover (if required)

Worm cover etch If you do wish to use one or both of the etched worm covers (note that we did NOT find that this was necessary in our test build, and for preference would use the original plastic covers), remove the cover etch from the fret.

Fold-backs soldered Having first fluxed the inner surface of each fold-back, make the 180° folds, with the fold line on the inside of each fold, at the corners of the etch. Hold the folds closed and secure them with solder.

Cleaning excess solder Clear any excess solder from the inside faces of the cover.

Folding cover sides Fold in the sides of the cover.

Folding bearing retainers Fold in the end bearing retainers of the cover.

Solder reinforcement for upper folds Strengthen the folds around the top of the cover with a touch of solder.

Remove the plastic worm cover and the worm shaft/bearing assembly from the Drive Unit.

Etched worm cover fitted Fit the etched cover over the four plastic upstands of the Drive Unit. Fettle them, if necessary, so that the cover slides easily over them and engages its slots over the lugs on the upstands. The etched cover isn't as flexible as the plastic original, it tends to splay a little and hang on to the lugs 'by its fingernails' - this is ok as long as it is secure.

Unclip the etched cover, re-fit the worm shaft and bearings, and replace the cover. Repeat the process, as detailed above when fitting the plastic cover, to check for freedom of rotation and end-float of the worm shaft, again relieving the circular edges of the cover's bearing retainers if necessary.

Final Assembly

Pivot / Tag washer If you have the etched bogie parts electrically 'live' to one rail for pickup, solder the feed wires, from the loco's circuit board, to the tag on each upper Pivot / Tag Washer (P2).

Take one bogie, with its drive shaft, and clip the correct end the shaft into the drive socket of the bogie.

Pivot assembled, top view Offer up the bogie into the aperture at its end of the loco. Route any pickup wires through the holes in the chassis block. Engage the free end of the cardan shaft into the loco's flywheel drive socket and line up the bogie top pivot with its pivot hole. Position the insulator and washers in the pivot hole and fit the retaining screw.

Similarly fit the other bogie.

Connect any loose pickup wires to the correct terminals of the circuit board.

Place the locomotive on some track and give it a test run under power.

Run the locomotive in gently at first. If the loco does not run freely or begins to bind up at any point, pay particular attention to lubrication of the axle bearings. You can feel for any binding by rotating the wheel rims with the fingers - there is enough slack in the drive train gears that you should be able to distinguish between a binding and a free wheelset.

When you are satisfied that the loco is running OK, and that this is the final assembly, remove the pivot screws and apply a thread locking compound to the threads of the captive nut in the top of the bolster (you can use a proprietary compound, but cyano glue, paint or even nail varnish will do the job). Replace the pivot screws, tightening them only so far as to put a slight preload between the bolster top and the pivot plate, whilst retaining a reasonably free (it doesn't have to be loose) pivoting movement. Give the loco another test run through some pointwork to make sure it's free enough.

Modified speaker enclosure Refit the speaker enclosure at the radiator end of the chassis block. The pivot components are arranged to just fit under the speaker enclosure, if you machine away most of the thickness of the original moulded dimple raised over the pivot screw. If you are taking power feed through the pivot screw, you can make an additional channel through the speaker enclosure moulding to take the connecting wire.

Finally, replace the body of the locomotive. Place it on a level surface and adjust the alignment of the cosmetic bogie frames with respect to the underside of the body. Secure the frames with a couple of spots of glue when you are happy with them.

All being well, thats it! - the modifications are complete and you have a(nother) sprung diesel loco.

IMPORTANT NOTE: If you need to remove the body subsequently, please DO NOT at any stage attempt to pull the chassis from the loco by pulling on the bogies, as this may damage the spring mountings.