Re-wheeling a Dock Shunter

I have a soft spot for Tri-ang Hornby Dock Shunters. As a child I had a train set, an oval of track with a Hornby LMS 2P and coaches, but this was a joint Christmas present between my brother and myself. For my 5th birthday I was given a black Dock Shunter, which I still own and cherish and is in original condition complete with its box. I have a plan to re-wheel it, those steamroller wheels have considerable presence but do spark a lot and probably aren't great conductors. I also have a second Dock Shunter, a red example with a damaged bufferbeam;

This was going to be repaired, converted to EM and given a fake modern BR livery to run on a proposed modern image layout that myself and a friend planned to build, purely to irk the purists. The loco was stripped down, the layout never happened, and its sat in the loft in pieces for 20+ years. My new plan was to use it as a guinea pig, replacing the wheels with something finer, and if it works doing the same to my original loco. When finished the red loco will have a place pulling a couple of Battle Space wagons around.

The first job, after re-assembling it to check that all the parts are there and it still works, was to remove the keeper plate and drop out the wheelsets;

Note that one axle has knurled wheels (what was that all about?) and a brass gear and the other smooth wheels and a nylon gear. Also in the photo are the Romford 14mm plain disc wheels that I'm using, which although small in comparison are actually only a millimetre smaller over the tread.
Then the old wheels were pulled from their axles, along with the worm gears, using GW Models wheel and gear pullers. I stripped the rest of the unit down as well, to repaint the chassis block, and whilst the armature was out I spun it in the lathe and polished the commutator with very fine wet and dry, moistened with a little saliva;

Cue gasps of horror! "You Sir, are a Madman, it will Never Work Again!!" they shout, spitting tea all over their laptops. The varnish looks a little worse for wear, but it runs so I'm leaving it alone.

Back to the wheels. Romford wagon wheels come with 2mm axles, the Dock Shunter's axles measure 3.57mm (9/64"). The Romford axles were faced to 20.2mm long, and brass bushes turned to suit the gears and reamed out to 2mm. With the gears fitted these could then be Loctited onto the axles;

Top hat bearings were then turned to fit into the chassis block;

These are reamed out to 2.02mm.
Romford wheels have insulating bushes on both wheels, for this project I needed one wheel to be live. So, the insulating bush was pressed out of two of the wheels and a brass hub pressed in instead. Then the wheels could be mounted into a watchmakers step chuck and the back of the hub faced and the wheel drilled and reamed to 1.97mm;

The wheels could now be pressed back onto their axles, trapping the top hat bearings in place;

And placed in the re-painted frames;

They roll quite nicely, with just enough sideways play. Paint is just car body primer.

Re-assembling these motor units is always a tad tricky I find, the hardest part juggling the armature bearings with their tiny ball thrust bearings and locking them in place with the metal spring clips without losing anything, one ball did disappear, luckily I have an old Tri-ang DMU motor bogie which was aquired as a source of spares - thank you Les. The same DMU unit also donated its magnet as the original seems to have lost some of its magic. I did some extensive bench testing with the armature in place but without wheels to make sure that the motor worked as it should, which is just as well as there was a bind on the armature bearings on one end, cured by wiggling the shaft with a pair of pliers until it span freely. I left off the oil retaining fabric washers that surround the sintered bearings, a drop of good quality clock oil should be all that's needed.

The keeper plate screws tend to bind on these locos, so before I re-assembled it I ran an 8BA tap down the threads. I also put a drop of cyano on the new brass axle bearings to stop them rotating in the chassis.

Here it is on the rolling road;

At the moment it runs better in reverse that forwards, something that time running on the rolling road will hopefully sort out. There's a slight 'clunk' on the brass gearset, and the un-modified insulated wheels are slightly out of true, but it runs well enough for me not to worry too much. I should also tidy the wiring up (does it really need those extra bits?) and fit a new lamp.
And finally, with the body in place;

The body retaining screw was missing, but that's not a problem because its 8BA which I have in stock. I also need to source a pair of couplings, then it will be ready for use. And I wonder how much difference a replacement neodynium magnet would make...

I'm calling this a success, I only intended it to be a test piece but it works well enough to prove the concept, and the wheels are finer and better suited to modern track.

I make no claims to originality, I remember reading a similar re-wheeling method in an old EM Gauge Society handbook.

Paul.

Postscript Dec. '21: This loco now has a new armature fitted to cure some pretty poor running - the original armature wasn't in as good condition as I originally though. At first I attempted to improve the running by fitting a neodynium magnet, but that wasn't the success that I thought it would be. Now however it works just fine.