Fixing the connecting rods

I shortened the overlong pins with wire clippers, then with a sheet of slitted card over the rod I fixed the nuts with tiny blobs of superglue gel. I thought that I might have to remove the rods sometime in the future, and superglue could be dissolved without damaging anything else here.

The nuts are much thicker than the prototype, and it was only after I'd fitted them all that I realised how clumsy they look.

Perhaps I could find something more subtle sometime.

Fitting the cranks

I've done a little background reading on fitting cranks and quartering them, such as descriptions of how people align the cranks by eye then "fine tune" them by rotating one wheel fractionally relative to the others.

I'm not sure how relevant this is. Since I've already got the balance weights aligned and quartered (by eye) I want to try to glue the cranks onto the wheels using the connecting rod as a jig. However there is some play between the gears, ie each axle can rotate a few degrees relative to the others, so there is no absolute "correct" alignment, and I expect that for this reason I may end up enlarging the holes in the rods to allow for the play. Time will tell.

Still I must mention one tip that I came across - someone uses a set of "loose muffs" so they can slide the wheels on and off easily for testing during construction. Wish I'd thought of that a few months ago...

"Work slowly and carefully", the instructions advise. I'll check things at each stage by making sure the chassis still runs downhill when I tilt my test-track in both directions.

First I check the fit of the crankpins in the rods, and have to open some of the holes out slightly so that the pins will fit through perpendicular to the rod.

Now I fit the first crank on, opposite the balance weight, making sure the pin is perpendicular. Waiting for the epoxy to set I remember I should have cut back the pins before fitting them.


Managed to cut the pin with wire-cutters. I allowed enough for the coupling rod, the fixing washer and a little extra to work with.

Next the front crank. As the glue sets I make sure I can turn the wheels gently. So far so good.


I've filed the first 2 extended axles back to allow the coupling rod to turn freely.

Then the third crank. The clearances are tight, but once I've removed every scrap of excess glue from the axles it still coasts downhill.


For the other side, I cut back the extended axles and crankpins as much as possible before starting.

Then I fit the cranks as before, with the rod still in place on the other side.

Well I'm happy to say, it didn't go that badly. I still have to fit washers to the crankpins (see the left axle above), but till then I'll keep the rods in place with plastic wiring.

Fitting the wheels

I've been thinking about how to fit the wheels for some time ("putting it off" might be more accurate). Seems that people have their own methods, and the instructions touch on this only briefly. I've looked at the design for a jig that fits wheels (and does the quartering) by tightening it a vice. But an Association member who builds his own locos successfully with relatively simple tools has described his method for fitting and quartering wheels which I plan to follow.

First file a chamfer on the end of each wheel axle


I'd already opened up the muffs with a 1.5mm drill. Now I need to drill a 1mm hole through the centre of the muff. This is to allow release of air as the tight-fitting axles are pushed in.


A final check that the chassis sides are still electrically separate, then I fit the first axle by turning each wheel by hand with gentle pressure inwards.


I've put a small washer on this axle to reduce sideways play.

I'd previously calculated that I needed a 0.45mm gap on each side between the wheels and chassis and now I need some spacers.

simple styrene sheet spacer

The key dimension is the distance between the back of the wheel rim and the chassis side. So the gap in the spacers has to be big enough to go around the small raised section visible around the axle, allowing the spacer to lie flat against the wheel. I cut some from 0.5mm thick styrene sheet.

Now with the spacers in place I can gently twist both wheels inwards until they are tight against the spacers. The first axle turns freely so I do the same with the central axle.

spacers on central axle

Now the gears are locking. Even though they had previously been running smoothly, I have to spend quite a while running the wheels along the test track by hand to loosen them up again.

Next to add the final axle, tighten the wheels to 8.5mm back-to-back (or just over) and turn the wheels so that the balance weights are aligned on both sides, with a quarter-turn difference between sides.

The coupling rods

The good news here is that because I've chosen to fit gears to drive all the axles, I don't need to worry too much about getting the coupling rods and crankpin relationship spot-on.

coupling rod etch

That small piece was loose when I first opened the box. I've been worried about losing it ever since so it'll be good to get this done.



Soldered, filed, the holes opened with a broach then finished with wet-and-dry.


The pins are a good tight fit, but I may need to make the holes larger to get things running when I fit the cranks on the wheels.


** May 2007 **

When I examined my prototype more closely I realised there was some more work to be done. The overlays around the crankpins are circular, and very thin. I tried to represent this by filing the overlays thinner and rounding the edges as much as I could.

the lower rod here has been trimmed

Fitting the crankpins

OK, I've changed my mind. Having thought a bit longer, I'm planning to fit the crankpins to the cranks, then fit the wheels then add the cranks.

Three reasons:

I'm finding it difficult to accurately fix the cranks parallel to the wheels.

I don't want to find that the cranks need to be adjusted further down the line.

I can make the crankpin joints stronger if I do them "on the bench".

And also, the instructions suggest doing it this way.

So, how to get the crankpins fixed perpendicular to the cranks? With the crank in a parallel clamp, I can hold the pin in the correct position with a finger while I solder (yes, the pin gets hot very quickly).



Then hold them in a drill chuck to tidy them up. I managed to get some solder around the sides of the cranks making the fold-over joint less obvious.


And now I can use the pins to help align the cranks on the wheels.

Checking out the cranks

I've decided to go with Humbrol matt black for the wheels. I'd rather use paint than any strong chemicals to colour the wheels, as they could get onto the rims and damage the running surface.


Just a first coat - I'm thinking I should fit the wheels before the second coat. But so far it looks quite pleasing.

I need to fit crankpins to the cranks and the cranks to the wheels. Opinion seems to be divided about what should be done before fitting the wheels and what after. The crankpins are so delicate, it seems to make sense to fit the wheels before adding them, but no harm in doing a "dry run" first to see what it all looks like.

crank etch

soldered and trimmed

As can be seen I had trouble getting a smooth edge on the cranks. Perhaps more solder would have helped fill those gaps?


trial fitting of cranks

There's plenty of room on the extended axle for the crank. Should it be close to the wheel or at the outer end of the axle?



With the wheels pushed closely together in the underframe, it looks as though there is still room for the crank well down the axle. Probably best to allow some margin for error though, so I'll put the cranks part-way down.

with a crankpin

These are a very generous length. I'm not sure exactly when I'll have to trim them, but even if I cut them short now, they'll still get in the way when I'm fitting the wheels onto the muffs.

Meanwhile I've realised, having painted the wheels, that I've forgotten to fit the balance weights.

Best plan now seems to be, to fit cranks and balance weights, re-do the paintwork, fit the wheels, get the quartering as good as possible by eye then add the crankpins and finalise the quartering.