This years loco project is based on a Bagnall loco built for service in India in the early 1920s. Nothing quite like it ran in Australia, so it carries the name of a well known Aust. cryptid.
Long time enthusiasts will be aware of the Roundhouse/GRS Gunga Din model, built from parts of the Fowler model and loosely based on a loco built by Bagnall for a mining railway in Burma. The only Bagnall tender loco. that ran in Aust. was 'Powellite' on the Powelltown Tramway, which was an outside cylinder 0-6-0. I had vague ideas of building one, but it wasn't on the 'must do' list.
Late last year I added a book to the library which had an illustration of the Bagnall locos built in 1921 for the Larkana Jacobabad Railway in what is now Pakistan. The line was run by the NWR and the locos became their S class. The design was later used as the basis for the very numerous Indian Railways ZB class. I'm not that much of a fan of the Roundhouse Gunga Din, but the S class was a very attractive, modern looking loco that could be considered as Gunga Din's better looking older sister.........
The illustration below was issued as coloured card by Bagnall, but searching also turned up a later photograph of one in service and some dimensions, so a Fowler chassis kit and various other bits were ordered from Roundhouse. We had a long hot summer and autumn, so I wasn't able to get into the workshop to start work on the loco until late April. The loco was built much as the illustration, but Australianised, with air brakes and the typical Indian louvred panel on the cab deleted.
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The model needed larger wheels than the Fowler, which meant a longer coupled wheelbase, so it was easier to make new frames than modify the ones in the kit. The model when finished will have the same wheel dia., wheelbase and boiler as a Roundhouse #24, so can be considered as being what Bagnall might have offered to meet the same specification. The photo shows the basic rolling chassis. I found a flangeless centre driver was necessary to get the loco around my minimum 4' dia. curve.
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The next photo shows the pony trucks fitted and the tender chassis built. The tender is the short UK style 6 wheel tender of the prototype and I tossed up whether to fit the bogie type Bagnall used on the Burma Mines Railway locos. I eventually decided that a modern superheated loco. wouldn't use as much water and coal as the older TVT Baldwins with saturated boilers and slide valves, so decided on the 6 wheel tender. The spring/axlebox castings on the tender came from Roundhouse, who use them in their 4 wheel tender kit and the smaller spring/axlebox castings on the pony trucks are O gauge parts from Walsall.
The tender wheelbase is actually 5mm longer than the loco fixed wheelbase, but the smaller wheels allow it to get around a 4' dia. curve without needing a flangeless centre wheelset.
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Valve gear was next and with a bit of work I was able to get the connecting rods and eccentric rods parallel and straight. The main change being a longer driving crankpin. I'd have liked to straighten out the radius rod and dummy combination lever, but this would require new valve chests and slide valves, at which point I might as well have made new cylinders and not bothered using Roundhouse parts at all. The running boards are typical of UK practice and took a while to work out and get a good fit between all the ups and downs in the valances. The part over the valve gear and cylinders is a separate piece, so it can be removed for easy access to the valves, without completely stripping the loco down.
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This slightly earlier photo shows the chassis ready for testing on air. The modified rods are visible, as well as the little bushes used to replace the star washers Roundhouse supply to retain the expansion links.
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The smokebox comes next and this had to be fabricated to match the prototype appearance. The smokebox door is made to open, which makes lighting up a lot easier. Dummy brackets to give the appearance of proper motion supports were also attached to the running boards by this stage. The chimney is a fairly simple turning job, but in this case a single piece, so a jig was necessary to hold the thing so both ends could be turned.
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Now it's boiler making time. None of the standard Roundhouse boilers are remotely suitable, so this shows the parts ready for assembly with silver solder. The boiler is the same capacity as the one on my Roundhouse #24, so the runtime should be similar.
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This photo shows the boiler after it has cooled down from the brazing and is ready to go in the pickle. All boilers look this disgusting straight off the hearth, but they clean up nicely after pickling. The wire ties are to stop the bushes moving while they are being brazed.
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Once cleaned up the boiler can be hydraulically tested. I'm slowly getting better at silver soldering and this one passed the test first time with no leaks. Another few days and the boiler is installed, the fittings in place and the steam piping completed. The small twin safety valves are a G1 design used on the boiler of the G1MRA ARMIG project design. They are a conventional design, but were used to simulate the twin pop valves on the prototype.
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Next job is the gas system. One of the minor irritants with the Roundhouse #24 is the small gas tank on the current version, so after some testing the size of the butane tank on this model was set at 40 ml and a tank and gas valve were fabricated. The gas valve is cunningly disguised as a handbrake stand.
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To be continued............
Graeme
