Drive train

Thoughts on the original drive train

Determining the needed gearbox and motor

I quickly settled on buying a gearbox from High Level Kits as they are generally lauded in the hobby forums. As this is my very first gearbox replacement I thought I would just go down that road. But determining which type needed some more consideration as there many different gearboxes for almost every conceivable situation.

First I set out to get to know the original situation and measure it out.

Frame, running board and motor loosely assembled ...

... to determine the dimensions of the needed motor and gearbox.

• will motor and gearbox fit in the loco
• will the motor's max rev. and the gearbox' transmission ratio lead to the a prototypical top speed.

These two interdependencies need some iterations to choose a suitable combination. I quickly aimed at Mashima 1424, with a max rev of 15,000 rpm, because it was the largest motor which could fit in with certainty.

The suitable gearbox in terms of size would be a LoadHauler+, which should be configured with a gear ratio of 60:1

Nice thing on the High Level Kits website is that it provides a gearbox profile sheet for your weapon of choice. You can download it and if you print it you will get a true to size drawing of the motor and gearbox.

I glued the two prints on styrene sheet and cut the sheet to size and drilled an axle hole.

This is how the LoadHauler+ with a Mashima 1424 should fit.

With the running board in place, still okay. I will probably need to cut the frames down where the original motor was.

And with the boiler placed, still okay, although it will be visible.

Ordering was easy. Communication with High Level Kits was fast and cordial. Knowledgeable questions were asked by the owner and subsequently answered by me. The order comprised a Mashima 1420 because these were in stock. Production of Mashima motors has ceased so availability of these motors will be increasingly difficult. The LoadHauler+ also has a small design change which will result in a 68:1 transmission ratio. As the Mashima 1420 has a slightly higher rev this is most welcome. A recalculation shows this:

So the new combination of motor and design change result in a spot on scale speed!

After confirming the order it took a good two weeks for the gearbox to arrive. It seems a long time in these super-quick-delivery-within-24-hours days` but do not forget that small companies like HLK are almost always a one man business. So I built the tender in the mean time. And then again, where's the hurry?

The kit came per envelope, greatly reducing postage costs. It was accompanied by a commendable instruction sheet, and a sheet with additional hints and tips. Considering the low cost of the gearbox, buying it was actually a no-brainer. The Mashima motor to go with it was more expensive.

Well this is the game for now.

• At the far left the old motor and end gear for comparison.
• Then the Mashima 1420 with its screws and the worm gear.
• At the right, rear the etch containing the main gearbox, the final drive carriage, some washers and two additional parts that are needed if the motor will not be directly attached to the gearbox.
• Right, middle row shows from left to right the first and second reduction gear, the idler and the end gear with it grub screw
• Right, front row shows two washers and the bushes for the axle
• At the far right you can see the steel axles for the gears and the brass wire that will close the gearbox and keep it in shape once built.

Building

Building starts with reaming the holes. Etching is a relative inaccurate process and it is good engineering practise to keep the holes in the etch a little undersize. So it my job to carefully enlarge the holes with a reamer, intially a few turns at a time but when approaching the desired push fit, one turn only and a trial fit after every turn. Here one axle bush already fits, the other remains to be done.

The parts are most easily worked when kept in their etch, especially the small parts, but that is also a matter of personal preference.

The holes that take up the steel axle on which the gears will run must also be reamed. The kit contains two hardened steel rods of the appropriate diameter. These are long enough to provide a sufficient quantity so a failure to make a correct axle does not immediately lead to a shortage of raw material. I cut my three axles from just one rod, gratefully preserving the second for future use.

Before you can ream the holes the outer end of the rod must be sawn off and smoothed. Why? Well, the rod has been cut with a cutter, not only snipping off a piece but also compressing the end of the rod at the cut. So at the cut the rod is completely out of form, rendering is unfit for testing while reaming. So

• cut a small piece off;
• file it flat;
• put it in a Proxxon drill;
• switch on;
• do some final filing to get it perfectly flat;
• and finally sand it smooth with 360 and 800 emery.

I also added a tiny chamfer on the edge so it will slide more easily into its hole.

◄ This should be the end result as opposed to the original rod

Now you have a suitable rod end, ream one hole until the rod just fits through, preferably to push fit.

◄ Success!

Before soldering the hole for the axle bush needs to be chamfered very lightly so the bush will fit in perfectly flat.

The bushes are soldered with a tiny amount of 180 C solder and the etch is cleaned up.

Done! A next to perfect final drive carriage.

After this stage the corners of the bending seams are filled with a fillet of solder.

Errrrrm,ah. Oh. The gearbox did not fit at all! The frame plates are 0.9mm thick,which is very thick by current standards. Currently most frames are only 0.5 mm thick and it was just this width multiplied by two that I missed. Now what?

There are several ways to go among which milling the frame plates down on the inside, 0.4 mm on each side, or simply making new frame plates from 0.5 mm sheet and adding new spacers. Both risky and laborious operations.

After giving it some thought I decided to move the washers between the axle bushes and the wheels (left drawing in red) to the location between the spacers and the inside of the frame plates (right drawing). This resulted in the frame being widened by 0.8mm while at the same time keeping the overall width between the wheels at the same value.

Standard

Widened

The effect on the frame was minimal. Who can tell the difference?

Standard

Widened

The valve gear bracket could pose a problem. But generally the DJH kits have liberal clearances in their valve gears and in case of emergency I could split the bracket in two and spread the two parts a little.

The brake hangers have the same issue and the same solution

With that issue settled I worked on completing the three steel axles on which the gears revolve. Each axle is first filed and smoothed as described for the steel rod end before reaming. Then measure out a little oversize of 10.1 mm, saw it off the rod and file it down to 10.3 mm and file and sand it smooth the same way as the other end. Aim for a length of 10.1 tot 10.2 mm.

Then the parts are laid out for a first trial assembly. A trial assembly is essential. You have to determine a good way of working for the assembly sequence. It is very nasty if you assemble it at first sight, apply the glue to find out only then you are working in the wrong order.

I started out with the axles inserted from the left and then working my way from the top to the bottom. That taught me two valuable lessons

• work with the axles from the right hand side, it is easier to pick the spacers first and then the gear;
• start with axle 3 with the idler on it, then work the two gears upwards from there and then install the final gear; which eliminates the fiddly "getting the next gear in between".

After trial assembly. The Blu-Tack is there to hold the axles in place.

When I was making photographs I realised I had forgotten to file the outside of the axle bushes down. The manual advises to file only so much down as need to fit between the frames in order to control lateral movement of the gearbox. Simply said, if you file to a fit between the axle bushes of the mainframes the gearbox will stay in place. As my gearbox really has no place to go between the frame plates I file both bushes simply flat :-)

Before we can turn to preparing the chassis we first must see how the gearbox fits in. The main choice is which axle to drive. First I explored the "classic" setup is proposed by DJH: motor pointing backwards and driving the third axle. To place the gearbox I had had to remove some material from the running board as again the gearbox was a tad too wide. White metal is easy to scrape away so that was quickly done. The photo is double first: the motor is on the gearbox for the first time and the gear box is in driving axle in the frame for the first time.

Two setups

In the left column is the classic setup

1. motor points to the cab;
2. Final Drive Carriage slung way from the motor;
3. connecting to the third axle

Alternative setup

1. motor points to the smokebox;
2. Final Drive Carriage slung towards the motor;
3. connecting to the fourth axle

Pro

• Relatively easy positioning of the motor
• Relatively easy placement and removal of the boiler

Pro

• The drive is almost invisible;
• Flywheel in the boiler; smoothing the drive
• My guess is that their can even be a flywheel on the worm wheel side although that will require considerable extra effort.

Con

• No flywheel possible or maybe with optimum positioning of the motor a very thin and wide one
• Gearbox visible although the problem is already much less than in original drive; the gearbox will be black so it is less obtrusive, and there are no visible moving and unpainted parts. Yet the gearbox will block the view under the boiler
• Moreover the boiler underside needs extra opening up to place the motor sufficiently high

Con

• Motor sits relatively deep in the boiler, making it hard to position and impeding installation and removal of the boiler.
• the propagation of the play in the drive of all five axles is not distributed symmetrically: the
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  I am not sure if this really is an issue. I build the drives with a minimum of play and most drives are not symmetrical anyway.
  

There is even a third setup possible. The motor will be in the same position as in the right column, the alternative setup, but with the Final Drive Carriage slung towards the firebox, driving the fifth axle. In addition to the variant in the right columns I found this

Extra pro

• The main additional advantage is that the gear box is now completly hidden

Extra con

• I need to relocate the spacer for that though.
• The axle play issue is even further aggravated.
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