Re-Powering a Soho LARy H-1 Streetcar

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During our investigations into trucks for tram/trolley/streetcars, we purchased a Los Angeles Railway model H-1 streetcar made by S.Soho & Co. We had been advised that many of these models are no longer working properly as a result of split gears. This lead us to develop the LoBoy, partly to address the need for replacement trucks and also because the design would be good for new construction if used in combination with our range of motors, mountings and gearboxes.

An important benefit of the re-powering process is that after conversion both trucks will be driven by the motor/gearbox unit, not just one as in the original model.

A further benefit of the LoBoy design was that we could make it work in HO 3' 6" gauge so that modelers would have the option of converting their existing LARy models to run on 12mm track in the correct prototypical fashion.

So, to lead by example, we are going to convert our existing 16.5mm gauge H-1 streetcar to 12mm gauge and replace the original trucks with the LoBoy trucks and a new motor-gearbox combination. The same principles demonstrated here could be used for other cars.


The first task is to remove the brass chassis plate from the model by unscrewing the four screws securing the plate to the body. Save these screws. Now remove the two trucks and the original motor.

By gently springing the frame apart, remove the side-frames and their U shaped mounting frame from the trailing non-powered truck and the driven truck.

We need to save the cast brass side frames for use with the new LoBoy trucks, so I heated these up with a small flame torch and released the side frames from the U shaped mounting.

None of the parts removed so far, with the exception of the chassis plate and the screws that attach it to the body, will be required in the re-assembled model.

The picture to the right shows the old Soho trucks alongside the replacement LoBoy 12mm gauge trucks. The gauge difference is quite evident in this shot.

The brass side frames are then soldered or glued to the nickel silver mounting tabs on the side of the LoBoy trucks, as shown in the picture below. If gluing, use an epoxy adhesive.


Mark Out and Cut Holes in Chassis

The next step is to mark out the new positions for the trucks on the chassis plate. The correct distance between truck centers for a H-1 is 31 feet, but unfortunately, if we were to position the trucks at these centers, the trucks would not rotate sufficiently. The original trucks on the Soho model were placed at a very noticeable 22' 10" center, some 8' 2" short of the correct position. The best we can achieve, and still have trucks free to rotate properly, is 28' 1" centers.

This is only 1' 5" further towards the center of the car than the ideal position, or less than 1/4" in HO scale terms. We also need to cut out two sections in the chassis plate to accommodate the new motor and gearbox assembly. The following drawing shows the changes required.

The two new holes for the mounting of the LoBoy trucks are 3.5mm or 0.138". The nearest practical drill size to this is a 9/64 or a number 29. The cut-outs are shown in the following drawing in red. Note that the dimensions are shown in Metric first and decimal inches in brackets.

After marking out the holes, we found the most effective way to cut out the brass was using a cut-off disc in a Dremel tool, as shown in the following picture.

Mounting the Motor/Gearbox

Clean up the hole edges with a file and de-burr the edges. The motor/gearbox combination we will be using is the 10 Series Half Floor Gearbox, fitted with an MHK-1024 motor and flywheel. This is the most powerful motor in the Mashima 10 series range, and when combined with a 1.8:1 gearbox, gives a total drive ratio of 27:1, which is pretty right for streetcar use.

This motor/gearbox combination is quite compact, and as the picture to the right shows, quite a lot smaller than the motor originally fitted to the Soho model.

The motor section is almost exactly half the height of the old motor and approximately the same length, but ends up longer because of the flywheel.

The 10 Series Half Floor Gearbox has an extended gearbox that translates the drive down to beneath the gearbox and provides a drive in both directions, so that both trucks can be powered. This also means that less of the motor/gearbox is visible in both the saloon section and also under the car.

Unfortunately, the rather large mounting hole in the chassis plate, plus the existing under floor detail, do not allow the 10 Series Gearbox to be mounted using the holes in the gearbox mounting flange.

We also need to raise the gearbox approx. 2.6mm or 3/32" above the existing chassis plate to make the coupling shafts line up better.

We found the best solution was to solder two lengths of K&S 3/32" square tube, part number 92021, to the chassis plate at the sides, and then tack solder the mounting tabs of the 10 Series Gearbox to the top of the tubes. Each piece of tube only needs to be 20mm or 3/4" long. This spaces the gearbox above the chassis plate near to the exact amount to line up the drive shafts. The position of the two sections of square tube is shown in the drawing above in green. Note that the tubes are spaced in from the edge by about 1/16" to clear the reinforcing strip on the inside of the body. When soldering in this area, take care not to dislodge the under frame detail parts soldered to the chassis.

If you have trouble getting this tubing, drop us an email to and we will send you a couple of pieces free of charge.

An alternative method of mounting the motor is to use two pieces of 60 thou styrene instead of the square brass tube, and fasten the motor/gearbox to these using double-side servo mounting tape.

When positioning the gearbox in the chassis, simply align it as close as you can to the center of the hole in the chassis plate. The exact position is not critical.

Fitting The Trucks to the Chassis

Now the trucks can be attached to the chassis plate. Refer to the following diagram:

The LoBoy as supplied is suited to two rail or overhead wire operation, as the wheels are insulated on one side. The body or frame of the LoBoy is connected to the wheels on one side, so it may or may not be necessary to insulate the mounting from the chassis plate, according to which type of operation you use. The mounting kit supplied with the LoBoy has a selection of parts for attaching the LoBoy to the chassis plate and can accommodate either method of power collection.

The diagram at left shows the order of assembly of the parts for an insulated mounting, ie, where the truck is fully insulated from the brass chassis plate. If you do not want an insulated mounting, then the method on the right can be used. There are 3 of the large nickel silver washers supplied, the reason being so the depth of thread in the LoBoy bolster can be regulated. It is important that when the fastening screw is tightened, very little of the screw protrudes out the bottom of the LoBoy bolster, otherwise it will foul the universal joint cup. If too much protrudes, insert another washer on the top of the stack.

Making Up the Shafts

Now invert the chassis and line the trucks up straight, in line with the chassis. To determine the length for each cardan shaft, measure the distance from the end of the slot in the universal joint cup at the truck end, to the same point in the cup on the gearbox end. A set of calipers are best for this task.

Deduct 1 millimeter, 0.04" or a fraction over 1/32" from the measurement obtained. This is the length needed for the shaft. Cut the shaft to this length, then file or grind the flat onto each end as per the instructions supplied with the shaft. The flat is necessary to mate with the 'D' shaped hole in the universal joint 'bone' section. Apply a little Loctite 609 or 638 to the end of the shaft and push into the bone taking care to align the flat section of the shaft with the 'D' hole in the bone.

To fit the shafts to the mechanism, place the bone in the cup at the motor end, then turn the truck so that it is near to 90 degrees to the chassis. Lay the bone alongside the cup in the truck end, rotating the cup so that the spigots on the bone line up with the slot in the cup, then rotate the truck gently back to its normal position. The bone should slide neatly into the cup.

At this stage, it would be a good idea to apply power to the motor and check that the mechanism runs smoothly. The gearbox and motor, along with the LoBoy trucks should have been adequately lubricated prior to delivery, so it should not be necessary to lubricate them further.

Wiring The Chassis

The following two diagrams show the wiring for 2 rail DC operation and overhead power with trolley pole reversing.


Some comparative photos of the H-1, both before and after re-powering. Before:

And after....

Now the astute among you will notice that these are not the same model, and yes, there were two.

But notice that the trucks look much better in their new position than previously. There is virtually no mechanism visible either in the saloon section or underneath the model in the re-powered version. In fact, the motor is a full 3mm below the saloon window line. And both trucks are now powered, not just one.

Viewed from underneath the model, before:

And after:

You might notice that the drive shafts appear canted down towards the left hand end. This is because the drive shafts for the HOn3.5 trucks are slightly offset to one side in order to provide optimum clearance.

The maximum angle that the HOn3.5 trucks can rotate is a fraction under 20 degrees, limited by the cardan shaft striking the inner part of the wheel flange. At this angle, and with a truck spacing of 98mm, the model should negotiate curves down to between 5.5" and 6" radius. The HO version can rotate even further.

All up this job took many hours to complete as we were photographing the results as we went, but it is estimated that the whole job could be completed in about 4 hours of continuous work.

Good luck, and please send photographs of your completed models.

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