Sign my


5.3 Installing the drive rods and valve gear

Once the pickups have been installed it is time to add the motion gear. One thing is absolutely paramount: the drive rods and valve gear should revolve without any form of binding. All stories about "running in" are rubbish. Every single set of Walschaerts' valve gear has a zillion options to snag somehow. Get it right or your loco will be crippled forever.

There are three things you should do to get it right

  • Test your model thoroughly before continuing to the next step.
  • Test your model thoroughly before continuing to the next step.
  • Test your model thoroughly before continuing to the next step.


Good, having brought about this rude message, the good news is that not all too difficult when you work meticulously and accurately.

First I laid out the valve gear as I had prepared it so far. I thoroughly studied the manual to re-acquaintance myself with all the little thingies again.


Next step is blackening. I use Carr's "Metal Black for Nickel Silver" for that purpose.

First all parts are degreased as if they are to be painted.

Next a bath is prepared of appr. 80-100 ml normal tap water in a plastic container and about 0.5 ml Carr's Metal black is added. That is pretty much diluted and it will take all night for the metal to turn black. It is my experience that this gives the best results. Stronger solutions blacken the material more quickly, within minutes if you like, but it will not hold when you rub it and the chemicals will also affect the surface by corrosion and pitting.



WARNING: be aware that you are handling chemicals of unknown composition when blackening.

  • Do not eat while working with Metal Black.
  • Wash your hands (s)carefully after working with them.
  • Clean your working area
  • Avoid "eye contact" and rinse your eyes thoroughly if it might happen
  • Go see a doctor if someone swallows it.
  • For the environment's sake please take care to use no more Metal Black than necessary. That is another reason why diluting is a wise thing.

After the the blackening is completed, rinse the parts. Take care not to wash small parts away.

Dry the parts on pieces of paper kitchen towel. The discolouration may not be even. This is usually not a problem. I am trying to depict a well worn AD60 with neglected and oil stained valve gear. In reality this staining would never have been even.

If you don't like the result burnish it with a glass fibre pen and rebathe it for another night.


After drying give it a gentle rub with a dry silver polishing cloth. This will give the dull metal a nice oily sheen and on the edges it will rub away just a little of the black so the parts reveal there forms and details a little better.

On intricate parts I take a small part of the polishing cloth in tweezers. A little bit of gentle rubbing will do.


The rivet counters amongst us may notice that two drive rods are missing on the photo. They have gone for another night in Metal Black.

Now the assembly of the drive and valve rodding can start in all earnest.


A simple advice:

  • take one step at a time
  • test after every step if there are traces of binding
  • and if so mend them before continuing.

Do not be tempted to press on. It is not difficult, only slow.


First the coupling rods have to be fitted temporarily and the chassis must be tested for free running

If there are signs of binding locate the offending hole and clean it up a little with a reamer. A little bit at a time until the binding has gone.


Now the drive rods can be attached permanently. The manual remains silent about the miracle of how fix the crankpin washers to the crankpins. Only on instruction [26] there is some reference not to attach them yet. Not overly helpful. So how to fix them? Of course you could glue them with epoxy or superglue. If that is your tool of choice be my guest. The method below is to my humble opinion the most controllable.


For my NGG16 I developed a simple and effective way of soldering the valve gear and I prefer that method. The main puzzle is this: how do I solder some parts where others need to remain moving freely. Or to put it stronger: how do I prevent the whole lot getting soldered rock solid? It sounds grizzly but trust me: my method is accurate, repeatable and durable.

I could refer to the corresponding pages of the NGG16 project but for the sake of simplicity I'll explain the steps on the AD60.


Take a brush and put a thin layer of grease on the coupling rod and the crank pin below the coupling rod surface. I use Vaseline for it but I suppose any household grease would do the job. Do not smear the crankpin above the surface of the coupling rod!

Take a rather thick piece of paper. I use a pack of 3M sticky notes that I pre-drilled for the purpose. The drilled hole is kept a wee too small so it forms a tight collar around the crankpin.

Move it over the crankpin all the way down onto the grease.


Add a new thin layer of grease on the paper all around the crankpin without touching the crankpin itself.


The purpose of the grease and the paper collar is to prevent the solder from flowing anywhere else then where you want it.

Slide the crankpin washer in place
Add a little flux. Not more than necessary. The flux will react slowly with the grease rendering the whole protective setup useless. So don't take a coffee break after adding the flux!

Add a spot of solder. I used 140C solder so as not to

  • disturb the blackened coupling rod and painted wheels,
  • burn the grease
  • or scorch the paper.

For the same reason do not linger with the soldering iron. Simply touch, flow and go.



Carefully tear the paper shim away, making sure nothing of it remains.

The shim served two purposes

  • it carried the grease in two layers and formed a collar to prevent the solder from flowing onto the coupling rod and forming an unwanted join.
  • it added a small distance between the washer and the coupling rod resulting in a sufficient, controllable but not excessive amount of play


Now TEST if the chassis still runs without binding

If it does, snip the protruding part of the crankpin away...

.. and file flat and sand it with 400 and 800 grain emery paper.

Make sure you don't touch the surface of the coupling rod with files or emery paper. The coupling rod scratches easily, immediately betraying its nickel silver origin again.



Now test again if the chassis runs without binding

Only then continue with the other crankpins.

WARNING do not, I repeat DO NOT snip off the crankpin of the driving (third) axle because you will need extra length to take up the driving rod and return crank in the next steps.

NOTE: Before continuing with mounting the valve gear tighten the Romford wheel nuts, preferably with the special Romford tool. Secure each nut with a droplet of CA, because experience had taught me that these nuts tend to work loose. Once the valve gear is in place it is very hard to get to the nuts.

Now gently move valve gear assembly in place containing the drive rod, the slide bar, the union link and the valve piston. It takes some patience to persuade the two pistons and one spigot to find their respective holes.



Tie the back end of the radius rod to the bracket with a string of thin wire.

As we have already seen the kit is supplied with crankpin washers. I have a supply of top hat bearing of the correct size and I prefer to use these as they are far more subtle.
If necessary ream the big end's hole a little to fit the top hat bearing.

Like this.

Secure it with a piece of  wire insulation.

A simple test run. Everything should move effortlessly without binding.


Now comes a fiddly job. The radius link, the rear of the radius bar, the lubricator bar and the bracket shall all be captured on one bolt and secured with a nut. To attain that I temporarily secured that nut with a tiny piece of Blue-Tack. One by I moved all layers in place and I could screw it all  but tight (a little play should remain as the radius link must rock freely). The nut was secured with a tiny drop of CA.

Check again for free running

Now we come to soldering the big end of the drive rod and simultaneously the return crank. That poses the question: does the return crank LEAD or LAG?

Walschaerts valve gear. Source: Wikipedia


First: what is the return crank?

Well, that is the small eccentric (1) attached to the main (drive) pin together with the big end of the drive rod. It sets the valve gear in motion via a join to the return rod (2).


The purpose of the return crank is twofold

  • it reduces the circle that the return rod makes,
  • it offsets the actuation of the return rod by about a quarter of a revolution.

In some designs this return crank LEADS in other it LAGS.


The return crank LEADS when the join to the return rod reaches a certain point, say the highest point that is exactly vertical above the centre of the axle, first then followed by the big end of the drive rod a quarter of a revolution later.

It LAGS when the big end reaches this point first then to be followed by the join with the return crank.

In both cases the locomotive is by definition running forward.


How does that work out in the visual appearance? In the Wikipedia diagram above, the return crank lags. At assumes the yellow lined position in the detail diagram at the left. Were it to lead, then it should assume the red line position.


I had some confusing documentation about the AD60. I had a copy of a drawing of the AD60 from an article in the May 1966 issue of Model Railroader. It showed the return crank of the front unit lagging and the return crank of the rear unit leading.

Is suspected an understandable error. The rear unit is technically running in reverse when the locomotive runs forward.

Long studying of photographic evidence convinced me that the return crank on both units where lagging when the locomotive was running forward.

6029's front unit is  difficult to see, but other photos show a clear lag.

©2015 with kind permission of Rob Nesbitt, Junee

6029's rear unit show a clear lag

(when running forward, that is to the left)

©2015 with kind permission of Rob Nesbitt, Junee


Good, having established lead or lag I could start working on the model.

I moved a piece of paper over the crank pin, as demonstrated before. It was greased and a crankpin washer was moved over it.

I greased the outside on the crankpin bush. NOT the inside because it needs to be soldered to the crankpin. The absolutely tiny bush is handled with a tooth pick, with which it is later placed in the big end of the drive rod.
A second piece of paper is moved over the crankpin washer to create some extra play. This later proved to be unnecessary so I omitted this step with the other three valve gear sets.

The bush is inserted in the big end, and the big end is carefully moved over the crankpin. Take care not to let go the grease anywhere where solder should go. If in doubt, clean it and start over.

Then the washer is soldered to the crankpin with as little solder as possible.



Do not proceed if it does not run freely


The drivers are brought to their lowest post ion. The return crank is brought into position. Make sure it does lean too much backwards. If it does the top end of the expansion link (or radius link, no 7 on the diagram) will move too far backwards and foul the valve gear bracket causing a binding.

Solder if flat on the crankpin bush's surface.

Snip off the protruding crank pin and file it flat.

I will later chemically blacken it again

Then follows a final test run  
The lubricator lever was soldered to 0.45 mm brass wire which was soldered into the lubricator on the valve gear bracket.

The lubricator lever and the actuator were connected by soldering 0.3 mm steel wire on them.

The lubricator lever was far too long so I snipped off the round end on the bottom.

The described assembly of the valve gear was repeated on the other side. This happened with considerable swiftness. I have ironed out all trouble spots. I know exactly what to do and if I finish the model in the coming weeks there won't be many fences to jump.

The lifting links on both sides were connected to the bracket with a 1.0 brass rod and glued.
After the glue had set I snipped the centre part away, cut it short on the outsides and filed it flat.

Done! Only the actuation of the right hand lubricator needs to be soldered in place.

I relished at the looks of the completed unit and thoroughly enjoyed the end result. I ran it up and down my test track time and again just to enjoy the feel of a smooth running chassis. This is one of those hugely gratifying moment that makes all the trouble worthwhile. My personal motto is: You have a thousand reasons to hate a model and just one to love it: you built it yourself.

That one single reason outweighs everything.

Then with a big bang I came back to reality. I suddenly realised that I soldered the return crank on the second valve gear wrong. Its was leading!! The next day a quick pass of the soldering iron corrected that and the unit once again (test, test, test) ran smoothly. Phew!!

I now started working on the front unit. The photo shows the clutter on my workplace. It also shows how little space you need to pursue this hobby

DISASTER strikes again!

In a moment of distraction I snipped off the number three crankpin. As it was not soldered yet, awaiting further assembly, it was way too short ever to be used again.

I now will have to order new crankpins. This will take at least a week. In the mean time I will be working on the rest of the loco, hoping I can use my time until the new crankpins arrive

While waiting for the replacement crankpin to arrive I turned to the the axle covers
There was a lot of work in such tiny parts, 16 in all. Snipping from the fret, filing the sides, smoothing on emery paper on both sides and the blackening, drying, once more blackening and drying.