MY RECENTLY completed Eagle has shown herself capable of running well and made her first public appearance at the Reading Rally in 2011. Building and tuning Eagle has been a challenge but this is my first attempt and I’m thrilled to have a locomotive that already runs sufficiently well for me to hope that it’s performance will improve as I gain experience. I’m writing these notes primarily to encourage other beginners, but hope experienced builders may be interested and perhaps reminded of their early efforts.

Eagle is a Martin Evans design for a 4-4-0 tender engine based on the GNR(I) Glover compounds of the V class introduced in 1932. The Vs proved fully capable of accelerating the service between Dublin and Belfast, the route for which they were designed. With heavy use they gained a reputation of being expensive to run and were seen as uneconomic – bearing in mind the traffic requirements - in terms of fuel and maintenance prior to World War 2.

The War changed everything, and with the smaller, more economical, S class 4-4-0s unable to cope with the increased loads the Vs came into their own. They put in some creditable performances, and were so well thought of that they were rebuilt with Belpaire  boilers in 1949. One example of the class, Merlin, has been preserved in Ireland.

Eagle had been under the bench, 80% complete, for the past 25 years. The major step towards getting her on the track was passing the boiler test in May. This allows up to 60psi steam pressure and was decided on as my plan was to run mainly on garden lines where the 80psi design pressure might have been awkward to control. I am now looking at this again, wondering whether scenic running and passenger hauling are compatible.

The Martin Evans design gives a fairly simple but handsome locomotive, although there were errors - covered in Steam Chest, the magazine of the National 2.5 inch Gauge Association, where this article also first appeared. I made some changes to the published design, most being minor (and none involving the boiler) aimed at ease of build or ease of maintenance rather than improvements in performance.

The changes which would affect performance were the omission of a superheater (see later), and modifications to the ashpan.  As designed, the air to the fire had to come through two 0.25in. holes at the front of the pan, which quickly became choked with ash, and through a narrow horizontal slot at the back. On the advice of Roger Mills, whose version of Eagle runs beautifully, I removed most of the back section of the ashpan where it is angled upwards to clear the rear driving axle. Combustion was improved, and the only slight disadvantage was that the axle is now exposed to the ashes.

As a further aid to combustion, and again on Roger’s advice, I reduced the blast nozzle orifice from 0.125in. to 0.110in. This sharpens the exhaust, and should pull more air through the fire, but at the cost of increased back pressure in the cylinders.

Perhaps it is relevant that I gave more lead to the cylinder slide valve opening than is usually recommended – not based on any  theoretical ideas, but because I found she ran best with these settings when the valves were set on air. My hazy ideas of valve events and what happens in cylinders suggest that early opening to admission must also mean early opening to exhaust, which may reduce any possible problems with back pressure. Eagle is certainly free-running with a turn of speed I sometimes find alarming!

The biggest single improvement in performance, much to my surprise, came when I insulated and clad the boiler. Like most of us, I’m an admirer of LBSC, and remember him writing somewhere that boiler insulation and cladding in our size was primarily for appearance, and had little affect on performance. Not so in my case. From struggling to make two laps of a small club track (NLSME Colney Heath), the newly clad Eagle easily romped round six laps before I had to stop to attend to the fire and water. This was hardly a controlled test, and other factors probably played a part, but the difference was dramatic.

The insulating material came from Kennions (now GLR Distributors) when they were still trading from Railway Place, Hertford, and looks like thick blotting paper. Whatever it is made of, two layers of it , covered by thin brass sheet, has made a big difference.

Other beginners may be interested in how I fitted the cladding, as the Martin Evans’ instructions are rather meagre. He recommends 28swg. brass, but as this wasn’t available  26swg. was used.

A paper template  confirmed the size and positions of the holes for boiler bushes, and there were no problems forming the barrel using bending rolls. The firebox cover was easily shaped around a suitable piece of dowelling. I may have been fortunate with my material, as it bent readily without annealing. The barrel insulation was held in place by thin phosphor-bronze wire while I fitted the brass sheet – that on the firebox was glued using Uhu, the inner layer having holes punched for the stay heads.

The next problem was to hold the brass firmly in place while fitting the boiler bands. I had imagined making a sort of large Jubilee clip until a friend suggested using plastic cable ties, which were ideal. Thin brass strip suitable for boiler bands didn’t seem to be available, so on the advice of Jacqui at Blackgates, I used their 0.125in. by 0.015in. spring steel strip. Being stronger than brass, it was easy to drill the ends for 10BA screws and nuts, and then bend them at right angles to form lugs.

I couldn’t see any easy way to fasten the firebox cladding with bands, so tucked the bottom edges between the firebox and the running boards, the top being held firmly by two large washers under the safety valves. Not an elegant solution, but it works until I find a better one. Another approach would be to have the cladding held by the spectacle plate. This would have needed a lot of extra work at this stage and I took the easy way out, with the firebox cladding butting up to the spectacle plate.

You may have realised by now that I try to make things as simple as possible, using materials available and techniques that I think will work for me. Which brings me back to superheating – the decision to run on saturated steam wasn’t taken after study of the thermodynamics, but because I wasn’t confident I could make the Martin Evans superheater and persuade it to fit properly. I did start to make one, but baulked at the prospect of bending 0.250in. copper pipe to the exact shape needed to assemble it in a small smokebox.

In my version steam comes direct from the wet-header through a short  length (approx 3in.) of 0.310in. pipe to the cylinder inlet. This was easy to make and fit, and seems to provide enough hot steam to the cylinders. Perhaps surprisingly, provided the water level isn’t allowed to rise much above half glass, the exhaust doesn’t seem wet and the only showers from the chimney come when starting with cold cylinders (there are no cylinder drain cocks fitted).

The large superheater flue is restricted by a baffle plate at the firebox end which I hope evens out gas flow through the firetubes. This is simply a stepped bush, with six 0.125in holes, with a drawbar through to the smokebox where it is held by a nutted crossbar.

One benefit of using saturated steam is that cylinder lubrication isn’t so critical, the wet steam being to some extent self lubricating. Martin Evans didn’t give a detail design for the lubricator, only showing an outline. I made this by drawing on my model boat experience, and it seemed to work, but I was never confident in it and have replaced it with a larger one to the Ayesha II design.

My version of Eagle is still in the plain black livery – but so far without the red lining – carried by the compounds from 1932 until 1935, when the better-known blue livery was introduced. Eagle will eventually have nameplates and cabside numbers, and I know that it probably never ran with GNR on the tender. It should be GREAT (insignia) NORTHERN, but I haven’t yet located a suitable transfer.

I’m not too concerned about fidelity to prototype, as the Martin Evans design was only loosely based on the V class, the major discrepancy being the gauge i.e. 5ft 3 in. used throughout Irish mainline railways. For anyone  wanting a locomotive with more of the Glover style, fairly simple changes could be made to the front buffer beam, driving wheel splashers, cab roof, and tender sides. What is important to me is that it captures some of the elegant proportions and atmosphere of the original – what do you think?

This first season of running Eagle has brought many pleasures, greatly aided by the advice and support from members of the N2½GA, the Gauge 3 Society, and the NLSME. The main lesson learned was that it takes a several months of running to sort out the inevitable early problems and to gain experience of managing the locomotive on the track.

Being  a first attempt with a relatively small 4-4-0, lacking superheat and with reduced boiler pressure, my version of Eagle has already run surprisingly well, and has the capacity for further development. Steve Eaton has led the way and shown how, with Toby valve arrangements, Eagle’s performance can be transformed.

For the future I will be looking seriously at fitting a superheater and raising the steam pressure to 80psi. Other worthwhile refinements might be fitting cylinder drain cocks and a snifter. Alternatively, I may take another look at the parts for the Bonds Black Five that have been lurking under the bench for the past ten years!

After 25 years under the bench 
the Eagle soars
by Gerry Ackroyd