L.M.S. “Royal Scot” Class

Created: 17 July 2011

Last updated: 4 October 2011

Introduction

Back in 1967, Rivarossi produced an exquisite model of the “Royal Scot” train: coaches of various types and of course the iconic 4-6-0 locomotive. Unfortunately, the models were made to a scale of about 1:82. with some parts closer to 1:87. This strange ratio was unique and typical of the Rivarossi production of the Sixties. Surely, it managed to annoy both the OO and the HO modelers in equal measure.

Anyway, apart from the scale, they were beautiful models — they still are, even by today’s standards.  Even better, they can be decently used alongside with other HO models, provided that some modifications are made. This article focuses on the Royal Scot locomotive, and it shows you how to improve it and transform it into a almost correct HO model. It takes a progressive, incremental approach — it lists five possible alterations, each one addressing a specific problem, which can be implemented singularly or in different combinations.

The possible alterations, rated according to their complexity, are:

1. Simple remotoring of the original model, plus optional DCC operation conversion – easy.
2. Lowering the original model – complex.
3. Substituting the original tender with a Stanier 4000 gallons unit – easy.
4. Converting the parallel boiler original model into a tapered boiler rebuilt one – medium.
5. Completely replace the original transmission and move the motor into the firebox, plus DCC sound operations conversion – complex.

This article explains all of them in detail — but note that this is not a workflow sequence. It is up to you to decide what to do, according to the desired goal and the personal experience.

At the end of the article, a finished model will be presented — L.M.S. 6115 “Scots Guardsman”, in wartime black livery — which implements all points from 2) to 5).

Preparing for the job

The original model, 6140 "Hector", taken apart.

Any succesful modification or conversion of a railway model begins with the careful preparation of the model itself. For obvious reasons, the older the original model is, the more important the preparation work is going to be.

In this specific case, any Rivarossi ‘Scot’ model is at least 30 years old. Chances are that it has already been used on a layout or it has been stored for years. Improper storage might have damaged the model, or after intense usage something inside might not be at its best.

In any case, before beginning with any modification, it is wise to assess the general model conditions: check if it is working, if it requires a cleanup and if there are broken parts. The following sections summarize most aspects of the model maintenance and handling with a view towards modifications.

Dismantling the locomotive

To dismantle the loco, undo the large screw under the front bogie (align the purpose-made hole in the bogie connection bar) and the screw that connects the tender draw bar to the loco. There is also a substantial weight in the boiler, kept in place with a single small screw: check if it is not rusty or otherwise damaged. At this step, mind the transmission shaft between the tender and the loco. The Rivarossi model has the motor in the tender, which powers the middle coupled axle via a cardan shaft and a worm and spur gear. The cardan shaft is especially delicate, because it is made of plastic and it stays in place only if the loco is aligned with the tender. Bend the tender draw bar more than usual and the shaft will slip out of the cardan joints and fall off. Note also that it is not possible to put the loco on the tracks, if the transmission shaft is not correctly placed. If properly aligned, the shaft will go in without any effort: if resistance is felt, it means that the cardan joints are not properly aligned, and any tentative to force it in will result in a broken shaft.

Electrically, the locomotive picks up current from one rail and the tender from the other one. The front lamps are lighted. To provide the light bulb and the motor with the missing rail pickup current, the draw bar doubles as a two-ways electrical connection. It is a sandwich of a nylon core with two metal strips, one above and one below, electrically insulated.

The tender body is simply clip mounted on the frame. There are two retaining clips just above the axleboxes of the middle axle. Insert a flat screwdriver in the dedicated openings and gently spread a bit apart. A word of wisdom: the plastic, after 30+ years, can be more brittle than usual. Proceed with care and do not apply too much force. A simple 1cm x 2cm piece of cardboard, slipped between the shell and the underframe, will keep the notch from snapping shut again. The tender shell should now lift without effort.

Check all electrical connections for corrosion or dirt. Rivarossi did not use any kind of soldering or wiring inside the model. All connections are by surface contact and the power buses are made with lengths of steel metal strip, riveted to the underframe. Automotive-grade spray for electrical contacts might be useful — but use it sparingly!

The motor has one of the brushes electrically connected to the outer shell, which in turn is electrically connected to one of the two rails. Check for oxidation traces on the motor shell, as well as for the status of the motor brushes. Please note that the two brushes are of different design and material, and cannot be swapped.

Check the lubrication status of the whole transmission: the worm and spur gear in the locomotive and the tiny cogs between the motor shaft and the cardan joint in the tender. The cogs are rather fragile and they may break unless kept properly clean and lubed.

Livery, cleaning and gluing

The model is moulded in black polystyrene plastic. It reacts well to normal polystyrene glue like the one made by Faller. It also reacts well to 2-parts epoxy putty (e.g. Milliput) and glue. Superglue, both liquid and gel types, also works well. The livery is made with some sort of acrylic paints, plus an overall layer of transparent protective paint. The transparent paint ages badly, with a tendency to chip and peel off over time.

Both the paint and the transparent coat will dissolve in alcohol, the transparent coat being a bit more resistant. To bare the model, put the shell into a sealable kitchen plastic bag, fill it with alcohol (e.g. meths) and soak it for a couple of hours, then scrub with an old toothbrush and some dish soap. Repeat until all paint is gone. A toothpick or a steel pin might be required to remove the paint from inside the many nooks the model has.

Caveats about removing the driver wheels

Special care must be paid when removing the wheels from the original axles. This is normally not necessary for the manteinance, and it is required only if the locomotive is being modified with a new motor in the firebox. I strongly suggest not to remove the wheels from the axles unless absolutely necessary. The original axles have longitudinal ribs that eat into the wheel’s plastic core. This insures that the wheel does not slip and lose the correct quartering, but it also prevents any quartering adjustment after the wheel has been pushed on the axle. More crucially, the ribs cause the axle to be almost seized into the wheel: when using the usual wheel extractor, the axle will not slip out, instead will pull the wheel hub with itself, breaking the spokes. On my model, I had to rebuild two spokes by hand with an accurately shaped plasticard piece, while trying to keep the wheel centered — a nightmare.

To safely remove one wheel, sandwich it between some stiff and flat material, e.g a scrap piece of PCB, with an appropriate opening for the axle — a slot just wide enough to let the axle trough, but not more. Lock the wheel extractor on this sandwich and gently wind up the plunger. The PCB will spread the load on the whole wheel instead of just the steel tyre, and the delicate plastic spokes will be relatively safe.

Part 1. Simple remotoring of the original model

The simplest modification to the ‘Scot’ is the replacement of the original motor with a more up-to-date unit. This procedure does not correct any dimensional error, but creates a nicely running, DCC friendly model. It will appeal to the modeller which wants to operate the locomotive on a layout and is willing to overlook the size discrepancy.

The original Rivarossi motors are very robust and were quite nice for the time when they were built. Still, the locomotive could surely benefit from a more modern unit, with better electrical and mechanical characteristics and more torque. A perfect replacement is the Mashima MHK1024, which allows a conversion without modifying the original parts. Apart from improving the running characteristics, it leaves some space in the tender for a DCC decoder and some additional ballast.

List of materials

• 1x Mashima MHK1024.
• 2mm brass or plasticard tube.
• 1mm plasticard plate.
• 1.5mm plasticard plate.
• 0.3mm electrical wire.
• adhesive tape.

List of tools

• Soldering iron.
• 2mm drill bit.
• Modelling knife.
• Flat and Philips screwdrivers.
• Needle pliers.
• Power drill.
• Fine-toothed metal circular saw.
• Fine-toothed jeweller’s files.

Procedure

If not already dismantled, remove the cardan shaft between loco and tender. As said before, this is very easy: actually the cardan shaft falls off by itself if the locomotive is not kept level and in line with the tender. Set aside the shaft.

Unclip the tender body by undoing the two retaining lugs located just after the middle wheelset. Use a 2mm flat screwdriver to gently enlarge the tender body sides, then pull upwards.

Undo the two screws holding the motor gearbox. Lift and remove the motor and gearbox assembly. Gently pull the black plastic cardan socket from the gearbox output shaft.

Take the Mashima motor and shorten the protruding front shaft, leaving a 3mm long stub. The original Rivarossi shaft is larger than the Mashima, so the cardan socket cannot be reused straight away. There are two options:

1. adapt the Mashima shaft, or
2. adapt the Rivarossi socket.

Both methods involve the creation of a suitable collar to be inserted on the Mashima shaft. In both cases, the brass or plasticard tube is used.

Option 1) is slightly fiddler but preserves the backward compatibility with the original Rivarossi parts. This might be important if you are not confident about the final result and want to keep the option open to revert back to the original status.

Option 2) is simpler, but it requires some more work to convert back the cardan socket to the Rivarossi standard.

A plasticard tube is easier to work with and, as it is elastic, it makes a snugger fit. The brass tube is more robust and allows more precise diameter control when fabricating the parts.

Dry-fitting the motor location.

What I personally tested, is option 2) with a brass tube. Whatever option you decide to use, you should end up with something like the picture on the left.

To adapt the Mashima shaft, cut a 2mm long tube collar, slide it on the motor shaft and glue it in place. Power up the motor, hold it steady with one hand and gently file the new collar external diameter to match the cardan socket bore. Finally, glue the socket in place.

To adapt the Rivarossi socket, cut a 2mm long tube collar, slide it on the motor shaft and glue it in place. Open up the cardan socket shaft bore to 2mm, and glue the socket in place.

Motor installation

Electrical connections.

The power supply to the original Rivarossi motor uses two simple metallic tabs, slightly sprung, which touch the motor outer shell — electrically connected to one brush — and the other insulated brush. Solder two lengths of thin electric wire to the end of each of these tabs: anything between 2cm and 5cm will do perfectly. Solder the other extremities to the Mashima motor terminals.

Mashima new motor in place --- front view.

At this stage, you might wish to go the extra mile and fit a DCC socket. It is a simple and inexpensive procedure: just wire it accordingly, and omit any wiring related to headlights, as the only one available is in the locomotive and hard-wired into the motor supply.

Mashima motor in place --- top view.

Cut a 35mm x 10mm adhesive tape strip and stick it on the horizontal power supply strip — this will insulate the Mashima motor casing. Prepare a 10mm x 5mm x 1mm plasticard tile — this will go between the adhedsive tape and the motor, to keep it horizontal and aligned with the original output shaft position. Put the Mashima engine in place, the flat sides being spaced just right to sit in between the underframe sides. Push it forward as it gets. It should rest against the two little vertical rims just before the coupler pivot.

Overview of all parts.

Finally, prepare a 23mm x 12mm x 1.5mm crossmember, with a couple of 17.5mm spaced, 2mm diameter holes. Using the original transmission screws, lock down the Mashima motor using this crossmember across the original mounting points. When fully tightened, the crossmember will warp down at the extremities: it’s OK, but of course one could also fashion a better shaped crossmember, with a contour to match the motor casing.

Test that the motor runs free, close the tender by clipping back the body in place, and reinstall the cardan shaft.

The locomotive is now ready to enter service.

Post-part 1 considerations

DCC operations

If you wish to install a DCC socket, there is plenty of space above the motor. Unfortunately, there is no easy way to connect the DCC light output to the front bulb, unless separate wires are threaded through. Also, when operating under DCC, the front bulb will be always on and operating at a higer voltage than the one it was originally intended; it might be wise to replace it with a more suitable one. The decoder itself can be placed behind the motor, or under the fake coal load. If you use a tiny decoder, there can be also place for a flywheel on the other motor shaft. This would require a bit of tender underframe surgery, though.

Consider also that the Mashima 1024 is a small motor. Most decoder with back-EMF control are preprogrammed with much larger, stiffer motors in mind, and the amount of back-EMF feedback is simply too much. The poor 1024 runs fine at speed, but will begin to kick and jerk at slow speed. Look in the programming manual of your specific decoder and decrease the CV corresponding to the back-EMF feedback loop. For instance, in my Bachmann EZ-command 3 functions decoder (art.# 36-553) the variable is 54. The default value (32) must be lowered to 8.

Weight and current collection.

The Mashima motor is sensibly lighter that the original Rivarossi. It would be advisable to add some lead pellets inside the tender, ideally under the coal, to preserve the original weight distribution. If one wants to preserve the original Rivarossi model, it is possible to prepare a plasticard box of adequate shape and size, fill it with lead pellets and fix it inside the tender with some sort of removable glue. Anyway, this does not solve the basic problem of this model: the lack of a reliable current collection.

As described before, the current pickups are split among the locomotive (right rail) and the tender (left rail). Given that the loco has a rigid frame, there can be at most two active wheel pickups on the right rail and any given moment. The same applies to the tender, but here the middle axle is sprung and the other two have some play, so three pickups on the left rail are usually available. Clearly, this is less than optimum for a locomotive with 16 wheels!

The best solution would be, of course, to fit all wheels with electrical pickups, but this would require some major modification. It is much easier to extend the tender pickups — it just takes some phosphor bronze wire or strip, or the Gibson sprung plunger pickups (e.g. from MainlyTrains Art. # GI4M062) and a little surgery in the tender underframe. To fit the Gibson pickups, just drill suitable holes vertically over the wheel threads, then glue the pickups in place. A plain phosphor bronze strip is even simpler to fit, just glue it in place and thread a wire through the underframe.

With a full six wheels pickup, plus the odd one or two from the locomotive, and some additional weight in the tender to push the wheels firmly onto the rails, there will be no more problems of current collection. Of course, this step requires some small but irreversible alteration to the original Rivarossi model: notes and pictures of the tender underframe so modified can be found in Part 4.

Part 2. Lowering the original model

The most obvious error in the original model is that it rides too high on its wheels. The cylinder centerline should be in line with the wheel hubs, and this is clearly not the case. The whole machine sits about 1.5mm too high, and this is consistent throughout: buffers, tender axleboxes, cylinders.

It is possible to lower the locomotive without spoiling the paintwork. This procedure was pioneered by the late Malcolm Carlsson, and here I am following in his footsteps, adding a few more improvements and remarks to his already excellent job. It is important to remark that this is potentially fatal alteration: a gross mistake here will cost the model functionality. For this conversion to succeed, the key is to proceed slowly and without hurry.

The procedure basically requires all axles to be pushed inside the frames by an additional 1.5mm. This is done by eating away some plastic from the axles seatings. In the tender, this is very simple: there are plastic steps that keep the axles in place, and their height happen to be just about the right amount: just remove them with a mill in a power tool. Work gently without heating the plastic, and there will be no problems. I left the rearmost axle rigidly mounted in the frame, while the frontmost one rests on a central pivot and is free to slightly rock. This gives the chassis a degree of compensation, improves the riding quality and the current collection. The middle axle is sprung and carries no weight: it can remain so, but because of the new axle position, the original coil spring that keeps it on the rails has to be shortened.

Lowering the locomotive is trickier. As with the tender underframe, there are plastic steps that keep the axlebearings at a certain height. They have to be shortened, but the locomotive chassis is rigid and the precision here is mandatory. I found a procedure that can help a lot: dismantle the loco completely, then clamp a steel edge along the undeframe side to mark the depth of the cut and to stop a cutting tool from eating too much material. Even when using a file or a mill bit, the steel edge will act as a guard and it will avoid irreparable damage.

The transmission worm and its cover must be also raised by 1.5mm. Here fortunately the worm is mounted on brass bearings, press-fitted in the frame. Packing some plasticard bit of the appropriate thickness will solve any problem, and, as it is not necessary to glue it,  it is possible to experiment with different sizes until the best one is found.

Notches in the motion subframe.

Inverted pilot suspension arm.

The drivers rims will now foul the metal subframe that carries the distribution. Notches have to be filed until the first driving axle can roll freely.

The front pilot bogie has a suspension arm that will no longer sit properly when the loco is lowered. The arm works better if attached under the bogie, not above as in origin. I simply filed the original rivet, dismantled and reassembled the unit and reinstalled the original rivet upside down, securing it with a drop of superglue. Of course, do not let the glue lock the bogie.

Behind the drivers there are the plastic reproductions of the real suspensions. This plastic protrusions are now much closer to the rails and when passing over points they can foul the check rails. Shorten them, or cut them off altogether, as they are practically invisible.

When lowered, the machine dramatically changes face. The motion rods rest in a more natural position and the huge gap between pilot bogie and underframe disappears.

Lowered vs. original.

Part 3. Tender replacement.

Replacing the ‘Scot’ tender is another job that is comparatively easy, does not require special skills and is perfectly compatible with all other modifications described so far.

The real locomotives begun to receive the new Stanier 4000 gallons tenders soon after they entered service, and long before the decision was taken to rebuild them. Compared to the original Fowler 3500 gallons units, the new tenders were wider, slightly longer and definitely bulkier looking than the old ones. As the Rivarossi tender is built to a 1:82 ratio, it turns out that the basic dimensions and underframe are actually closer to a Stanier unit than to a Fowler one. There is both the motive and the opportunity to replace the tender, and in a benevolent turn of fate, the means to do it are rather straightforward.

A major help in the reconstruction would be the availability of the excellent drawings from J.Roche. They can be used straight away as templates, and I actually copied them onto some stiff paper and produced a mock up shell to test the major dimensions and the shapes of the single parts.

Alternatively, there used to be a HO brass and whitemetal kit of a ‘Black 5’, made by Mick Scarrow and Phil Rivers and available through the British 1:87 Society, which has the same tender required here. The photoetched parts could be used as templates for the production of the plasticard parts required here.

Whatever method you use, the results will be similar: the Black 5 parts near-perfectly match with Roche’s drawings.

Modifications

There are basically two areas affected by the modifications: the shell itself, and the axleboxes. All parts are simply snap-fitted onto the underframe. The shell removal has already been deal with in Part 1, and will not be repeated here.

Axleboxes

New tender axleboxes in detail.

The original axleboxes are simply pressed in place. To remove them, just slide a thin blade between the axlebox and the underframe, and gently wiggle until it lifts. Save the original axleboxes for other projects, and replace them with correctly shaped new ones. Possible sources are undersized OO or oversized TT models, but again the best option is to use the parts made for the Black 5 kit. As the kit is no longer in production, I used the six white metal originals as masters for a silicon mould, then I cast multiple copies in resin and glued them in place.

In the picture above you see the final result — although the casts are still marred by some bubbles and cracks, which have to be fixed.

The superstructure

Tender structural modifications --- back end.

Tender structural modifications --- front end.

The superstructure is first cleaned of all details on the sides and the back body plates. Then, rectangles of 0.15mm plasticard are glued in place to level off the body panels frames. Sand accurately to a regular, level finish.

Remove the metal caps that protrude from the fake coal. These are the vents covers which, in the real locomotive, allow air to escape from the water tank when filling up. They will be reused, so set them aside in a safe place.

Saw off the coal and the upper part of the coal bunker. I used a very fine toothed steel saw from X-Acto, but if you trust your hands you could also use a circular steel saw in a power tool. Whatever the cutting tool, you have to remove the ‘coal’, the sides and the rear bulkhead. The front bulkhead is cut around the large inspection doors and the tool boxes. Finally, cut out a crown piece (0.5mm thick) that fits the remaining bulkhead profile and has the correct rounded profile on top. See the pictures here above for more details.

Tender, right side.

Now the new sides have to be fabricated. Use two layers of 0.3mm plasticard per side. This brings the total body width from 28.4mm to 29.6mm. The back wall is a single 0.3mm layer. Make sure that the sides overlap at the joints with the back wall, glue accurately, trim to size and file to a straight, clean edge.

Use the Roche drawings for the general dimensions, but shorten the sides by about 2.5mm — this is due to the slightly shorter-than-scale Rivarossi underframe. If you spread the compression proportionately between the coal bunker length and the water tank tail, the overall shape is preserved and the size difference goes almost unnoticed.

Now draw, cut and glue in place the rear bulkhead, which will have the same outer profile of the front one and a notch in the bottom, to allow for the large cylindrical tank on the rear top plate.

When gluing the sides in place, remember to bend inwards the coal bunker upper borders. The curvature is such that the sides will stay correctly in place once glued to the bulkheads. The body panels close to the footplate are also bent inwards, but bending polystyrene here is a bit impractical. In this case, the curvature can be suggested by some accurate filing.

Tender, front end.

Tender, back end.

Finally, close the coal bunker with a flat piece of plasticard, slightly set in and glued from within the shell. This cap will support a layer of real coal, glued in place once the model is completed.

One of the most prominent features of his tender are, of course, the rivets on the bodywork. The Stanier tenders come in two flavours: fully riveted or welded. In both variants, there are long rivet lines in plain sight.

To model these realistically, I used the remarkable resin surface details from Archer Transfers (in this case art. # AR88025). These are resin details of different types (e.g. rivet heads, welding marks and lines, cast plates and mumbers, nuts and bolt heads, etc…) embedded on top of a clear decal film. They work just like decals, react well to setting agents like MicroSol and MicroSet (but beware that too much solvent will probably distort the decal and make more difficult to obtain straight lines) and they stick well even on slightly irregular surfaces. Of course, as they go under the paint layer, there is no need to worry about decal silvering or similar common troubles. The only recommendation is that, once dry and set, it is better to seal them with a coat of enamel so that the subsequent handling will not accidentally detach them. Once painted and finished, the final effect is very convincing.

The tender now lacks only the minute details. Here is the list of what I did, together with some short notes about how I did it:

• footplate and corner handrails. Simply made of brass wire threaded through Gibson knobs for OO models.
• handwheels on the footplate end. Recycled from a Dapol Mogul unmotorised kit (see Part 4. for more details about this).
• inspections steps on the back end plate. Made with L-shaped plasticard profile, suitably slimmed.
• water tank vents close to the rear bulkheads. Made with 2mm brass tube, capped with the original Rivarossi parts and cemented together with epoxy glue.
• roof over the foorplate inspection doors. Made with a 2.5mm wide, 12mm long steel strip, bent and filed to the correct shape and superglued in place.

Final remarks

The rear vaacum brake pipe is the Rivarossi original, slightly bent and adapted to the new shell holes. The white disks on the tender footplate are there to cover the former location holes of the handbrakes columns — a better solution would have been a full footplate cover, but this in simpler, quicker and it goes almost unnoticed once the tender is coupled up to the locomotive.

You might have noticed that the coal bunker top has some additional lead pellets glued on and a protruding black box in the middle. The lead is there to improve adehesion and there is also more of it glued inside. The black box is a resonance box for a loudspeaker, facing downwards, and you can ignore it unless you wish to fit DCC sound effects.

Once you are finished, and you try to put the shell back on the underframe, you will notice that the new axleboxes are wider that the originals and foul the corner steps attached to the tender shell. The solution is to saw off precisely the lower steps, clip the shell to the underframe, and reposition each step in the right place but glued to the underframe — use small rectangles of plasticard as padding between the underframe and the steps to bring them in line with the others. If the cut is done precisely, it will be completely invisible once the tender is fully assembled.

Option of cast resin tender.

The resin tender shell.

An interesting option is to cast the entire tender shell in resin. This modification does not involve the alteration of the tender shell interface so, if the silicon mould is properly designed, the resin piece will snap in place just as well as the original. The details about a full tridimentional resin casting will not be expanded here in detail, but the procedure is not as complex as it might appear. The key is to cast a shape with only the minimum of details required to speedup the job. In the picture here on the left it can clearly be seen that the mould was made before adding the rivets: it is a basic shape, where the casting imperfections (air bubbles, cracks, hairlines, steps, etc…) can still be sanded flat or filled in.

Replacing the tender shell with a cast resin unit would offer the possibility to produce a pre-WWII configuration: many ‘Scots’ received the Stanier tender well before being reboilered.Repainted in L.M.S. crimson or wartime black livery, it would make another interesting Royal Scot variation.

Part 4. General rebuilding.

Diring the ’40s, the Royal Scots were rebuilt with new 2A tapered boilers, new fireboxes and new cylinders. Basically, of the original locomotives just the frames and the cabs remained.

Having obtained a faulty Royal Scot “Hector” from eBay, I decided to experiment a little and try a full rebuild. Additionally, as the fault was to be found in the transmission, I also decided to remotor my Scot with a newer and more compact unit, mounted in the firebox.

This procedure, of course, completely destroys the original livery, and it is therefore a good chance to repaint the Royal Scot in a different guise. To keep things simple, I decided to paint mine in plain wartime unlined black.

The reconstruction leaves very little of the original model: underframe, running boards, cabin and the upper part of the firebox. A small number of key parts have to be source elswhere and I found that the venerable Dapol Mogul 2-6-0 unmotorised kit is perfectly suited for the job. Many parts of the Mogul kit have been already mentioned and used in the previous sections.

Begin by removing the old livery, as already outlined in the tender reconstruction, and completely disassemble the machine. Unplug the cabin and set aside. Pay special attention to carefully remove and set aside all small brass parts (whistles, valves, knobs, buffers, etc…). Note that the knobs come in two different lenghts: the three along the boiler are longer than the first two on the smokebox and the last two on the firebox. The knobs on the smokebox door are also of the short type.

The body shell, after boiler removal.

Using a fine saw, cut away the smokebox, the boiler and the firebox, and also separate all three parts. The cut should leave the running boards intact. You also have to save the drivers’ splashers and the sandboxes: it is up to you to decide if you wish to cut around them or separate them from the running boards and put them back in place at a later stage. My choice was to cut around the splashers and remove the sandboxes.

Detach the steam dome and the firebox door by pushing from inside the boiler. Now build the new boiler, following these steps.

1. Discard the original smokebox entirely. Assemble the boiler from the Mogul kit, then saw off the smokebox and clean it from all additional parts until left with the simple cylinder.
2. Remove the details from the Mogul smokebox door and reshape the new locking handle and hinges from bits of brass and plasticard. Locate the exact position for the handrail knobs and bore the new holes accordingly.
3. Remove a triangular slice from the top of the Rivarossi boiler, starting with a width of 1mm from the hole left by the steam dome and moving forward until the cut is 3mm wide. Bend and glue back the sides until the boiler is slightly conical. It is important that the new tapered end matches in diameter the Mogul smokebox. Brace all joint with 0.25mm plasticard strips, and apply polystyrene glue liberally — the joint must be rock solid.

The new smokebox and boiler --- bottom.

The new smokebox and boiler --- top.

Once the parts are ready, dry fit and adapt the matching surfaces until a satisfying fit is achieved. Plug the funnel and steam dome original holes with plasticard, then fill and sand all remaining holes and imperfections until a smooth surface is obtained. It might take a few iterations and a certain amount of plasticard and putty. Once finished, you should have something like the pictures above.

The new funnel.

The rebuilt Scots use a Kylchap double ejector funnel. Unless you find a suitable one, you have to build your own by assembling the Mogul funnel and interposing a 3mm section made of plasticard. Take care to match the profile of the original parts and file to a smooth finish. Once thoroughly dry, enlarge the inside hole until it can hold two brass tubes of about 3mm diameter. When inserting the tubes, you might wish to file flat the contact surface between the two.

It is now time to test and dry-fit all parts made so far. In the following pictures, you can compare the modified locomotive alongside an original one.

Rebuilt vs. original - side view.

Rebuilt vs. original - front view.

Discard the original smokebox entirely. Assemble the boiler from the Mogul kit, then saw off all additional parts until left with the simple cylinder.

Remove 1mm along the firebox bottom and the cabin bottom. Glue the firebox back in place: make sure that the front wall is securely glued, but leave the sides just barely fixed to the running boards. The reason for this will be clear in a few moments.

Recreate the cabin bottom curved shape, rebuild the raised rim with a thin plasticard strip and check for a tight fit with the shell. When the firebox front wall is securely dried, check that the cab still snaps back in place: is not, file and reshape the interlocking tabs accordingly.

Now comes the trickiest part of the whole reconstruction: model the characteristic firebox rounded belly. Glue the boiler and the smokebox in place and check for any weak spot or imperfection. Once the glue has thoroughly cured, cut away the bottom part of the firebox. Remove the firebox side walls from mid-height down to the running boards. As the rest of the body is securely glued, there will be no undue deformation. The job is best done with a fine steel saw in a power tool, but a simple X-Acto steel saw blade will work just as well.

Inside the rebuilt firebox.

Rebuild the missing sides with plasticard foil, using the boiler side as reference for the correct bend. As the new firebox sides are no longer fully vertical, the driver wheels splashers are fully visible: rebuild the missing part of the middle splasher and the forward half of the rearmost one. I found it easy to cut the required profiles directly from the Roche drawings, then presenting them against the locomotive shell and make all necessary adjustments. Finally fill all holes, cracks and imperfections with twin component putty (e.g. Milliput) and smooth out before it sets.

When you are finished with the sides, saw off the raised dome which carries the safety valves, plug the resulting hole and fill and sand as usual. Finally, inspect the shell under a strong light and sand everything to a smooth finish.

If you are also remotoring the locomotive, you have to make space for the new motor in the firebox. According to the size of your motor, saw off the appropriate measure of the internal lead ballast. Be careful not to remove anyone of the two screws seatings in the ballast itself: the rearmost keeps the ballast fixed inside the boiler, the foremost locks the entire locomotive shell to the underframe. If space allows, line the firebox with lead pellets, to rebalance the locomotive and compensate for the weight loss.

The finished shell - side view.

The finished shell - bottom view.

It is now time to add the cosmetic details. Please look at the pictures for a complete overview of all parts. The most significant ones are described in the following paragraphs.

The original steam dome and the funnel are glued in place. Some additional Milliput is used to obtain the correct shapes, slopes and blending lines. The smaller dome between them, actually a shroud for a top feed, is scratchbuilt with four bits of plasticard and some Milliput. The locomotive has also got new cylinder steam pipes made of 3mm brass pipe cut and filed to shape, superglued in place and finished with Milliput. The three cylinder discharge pipes are threads of brass wire, bent to shape and glued together. As for the tender, the rivets are from Archer Transfers.

The boiler details are from an assorted set of brass strips, 0.3mm and 0.5mm brass wire, plasticard, bits from the Mogul kit, and some creative reuse of the original Rivarossi details. Note that the two sides are visibly different, the right one being much less cluttered.

The remaining pictures show the complete locomotive during its final assembly.

The complete locomotive, ready for assembly.

Front ends.	Back ends.
The internals.	Left side view.

The electrical and mechanical details should be fairly obvious: the DCC decoder is housed in the tender and the motor drives the rearmost coupled axle. The tender uses the original current pickups, plus a vertically mounted one on the front righthand wheel, and phosphor bronze ones on the second and third righthand wheels. A custom-made 7-pins plug between tender and locomotive provides the electrical connections. A DCC 21-MTC interface is bolted to the tender underframe and it receives the electrical pickups from the tender wheels and the additional pickups in the locomotive.

The drawbar between the locomotive and the tender is shorter than the original one, and the locomotive underframe modifications require a revised way to lock the locomotive shell onto the underframe. A simple 1.2mm long bolt and nut acts as drawbar pivot and secures the shell in place. The nut is glued on the cabin footplate, just before the firebox doors, and is hidden under a small heap of coal.

The locomotive wiring has been completely remade: the front bulb is now connected to the decoder F1 output via the custom plug, and additional Gibson sprung plunger pickups have been added where possible.

The 21-MTC interface already provides two output pins for the loudspeaked: a suitable unit has been placed under the coal, facing down (see tender shell alterations in Part 3. for more details), and the wires connected via a loose miniature plug. The plug allows a complete removal of the tender shell in case of mainteinance activities.

The decoder is a Uhlenbrock Intellisound #36030, which I reprogrammed with a decent approximation of a rebuilt Royal Scot sound.

Finally, the tender has been fitted with a Kadee #7 coupler, which happens to fit in the original tender chassis quite nicely with a minimum of rework.

Here you can see a short video I took while testing the assembled locomotive before committing it to the paint shop.

Painting and decaling

The locomotive is finished in the wartime overall flat black livery. I have to admit I selected this paint scheme because of its simplicity — I just wanted to finish it quickly! The decals are home-made with an ALPS printer, using a Georgia Bold typeface, stretched and adapted to look correct. Strictly speaking, this typeface uses a different stroke style for the numeral ‘3’ with respect to the L.M.S. typeface; as my model represents 6115 “Scots Guardsman”, it does not really matter.

6115 --- front view.

6115 --- rear view.

Conclusion

Broadly speaking, I am pleased with the final result. Compared to the 1:87 exact measurements, the complete machine is correctly scaled in height, a tad more than 1mm wider, and about 5mm longer when measured buffers-to-buffers. To me, it looks and it moves as a rebuilt Royal Scot, and that is enough. There are nevertheless a number of imperfections and mismatches that cannot simply be corrected, unless the main structural parts are substituted with correct ones.

In retrospect, it was a mistake to put all these activities into one single project — remotoring, DCC conversion, sound, heavy reshaping of the outer shell, etc. For instance, it would have been much easier to limit the conversion to the shell and keeping the original inner workings. For me, this was also the first venture into the realms of DCC sound, and it took some time and effort to come up with a decent result.

Simply put, I would think twice before making another one in this way. Still, British HO outline models do not abound, and this one would surely fill a gap in any collection; so, if you can live with the inevitable inaccuracies caused by the original model and take a more cautious, progressive approach to the amount of things you tackle, nothings prevents you from trying and build your own.

Happy modelling!

6115