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More experience with the


 "Frank S"


by Elk Hartmann


Three years ago I bought my Aster Frank S, obviously second hand but still in quite a good shape. The decision to buy it was influenced to a large extent by what I read about this little engine on the Southern Steam Trains website. I always wanted to have an Aster engine. but only have enough space to run narrow gauge locomotive, so the Frank S was my choice AND it looks really nice.


 When delivered, I was concerned that it had been run without oil and was dry as a desert. However, inspection revealed the steam cylinders where in good condition.  If the piston valves had been worn out, then a new set of cylinders would be added to the overall cost. But I was lucky….


After cleaning and checking, it was time for the first steam up. Oiling and filling up with water and gas ticked of as done, RC system ready: here we go, the flame popped back and a steady mild roar started. After a short while steam was rising 1,0 bar -1,5 bar then 2 bar… then I opened the steam valve and nothing happened, then I pushed the stick of the RC-Controller to full forward… again nothing but then all of a sudden, it slowly moved forward…with a good plume…very nice!


Later I coupled several LGB cars to the engine and with about 2 bars of steam pressure it easily pulled them around my layout on the terrace. After doing 3 additional runs that day, I was sure my decision to buy it was right. I still enjoy the running the little engine.  You can easily give the RC-controller to friends for a try run with out any problems. It is easy to control, even on tracks with grades.  As long as speed is controlled derailments are avoided.  The ease of operation and control impressed a friend of mine who is now thinking about buying one. 


  • After awhile with fiddling with the engine became day to day business, but some little things started to annoy ….

  • Would like a little more detail, additional steam lines at the boiler, to make the look more “scale like”

  • No possibility to refill the boiler under steam

  • The plume of steam disappears after the engine, especially after the tank in the smoke box, heats up

  • And last but not least I did not like the use of warm water to heat up the gas tank in the tender. If you do not do this, the performance of the engine weakens gradually while the gas tank gets cooler and cooler, due to the vaporization of the butane..


Now then, what could I do?  Repairing and do modifications of my engines, I consider a main fun factor of our hobby.  I started considering possible cures. One major consideration of potential changes is that I did not want to permanently alter the locomotive too much with additional holes, etc. 


Refilling under steam was an easy modification.  I replaced the filling screw with a new one containing a valve ("Goodall" type valve).  It is very simple and works like the tube valve on a bicycle tire. The “valve” is a simple piece of silicone. Based on some photos I added some more dummy boiler lines (for the air pump) and additional brake hoses. 


 Exhaust Pipe


Now then, what next: The plume. My first idea was to simply remove the drain tank in the fire box. My other Gauge 1 live steam locomotives do not have a drain tank.  Even with the drain tank, my Frank S still spite out some water during start up. So the question is the drain tank really necessary?  


Then I decided to start with the fitting of an exhaust pipe. The original exhaust tube is small and buried in the smoke box. I bought a thin walled brass tube with an inside diameter of 7 mm, so that the new exhaust pipe slips over the exhaust tube like a sleeve. I cut off a piece of about 5 cm of length. The top end is closed with a brass plate, which is soldered on and filed to shape. Underneath I cut a couple of slots that perform as a steam outlet. At the lower part a larger square size hole was cut out, which is the water outlet. The speed of the steam is reduced and the vortex generated produces condensation. First steam trials revealed that it works very well. Even at temperatures of 27 -30 ° C in summer a good plume can be seen..


My next challenge was how to get rid of the water in the tender? Moving the gas tank into the engine’s cabin? Possible but not much room there and a new gas tank would be needed. Heat the gas tank with steam? That sounds well and needs some engineering work to be done. I think the guys with the model steam boats do that.


So let’s begin.  I left the new parts unpainted for a better visibility.  The idea is to use steam from the boiler and guide it to the tender to warm up the gas tank. An additional valve is needed in the new steam line controls the flow of steam.



A ”radiator” for the gas tank is constructed by copper tube, wrapped around the circular section of the tank. Two little holes drilled into the front wall of the water task, serve as inlet and outlet for the cooper tube.  A short piece of silicone hose will guide the mixture of water and steam overboard after its passes though the copper radiator.


To connect the heater in the tender to the engine, I also use a silicone hose, basically for three reasons:


Firstly it is flexible and allows for movements between engine and tender.

Secondly, as it is transparent, you can watch what is happening i.e. when the first bubbles of water flow through the hose, you see that the warm up process just started and needs further observation.

Finally, I consider it a safety feature. In unlikely case, the steam supply from the boiler cannot be controlled any longer (i.e. malfunction of the steam control valve), you can easily detach the hose from the radiator in the tender to avoid overheating of the gas tank.


Overheating must be avoided at all times because the butane mixture develops high pressure if heated up extensively pressure can raise beyond the safety limits if overheated. (see Kevin O’Connor’s article on Fuels for Gas Firing in the reference section)  The tank itself should not get warmer than lukewarm, which is also mentioned in the original documentation that came with the engine. It is still applicable, because the tank temperature matters and not the means of heating.


Close up of tender with heating lines


My next step was the installation of a steam valve. I bought one from a live steam supplier rather then building one myself. With a new bracket I attached it to the rear part of the cab


Layout of the new steam heating line with adaptor, copper tube and valve


Finally the main challenge: how to get the steam out of the boiler without drilling an additional hole into the boiler? Answer: an adaptor that sits between boiler and safety valve can work. The adaptor is a piece of solid brass (having the same outside diameter than the safety valve socket) with an M6 outside fine thread on the one side and an M6 inside fine thread on the other side. The inside passage of the adaptor has to be of the same inside diameter than the safety valve to ensure the proper function of the safety valve.  The new heating steam line is connected laterally to the adaptor. I used a 3 mm copper steam line that connects via a M4 fine threaded nipple to the adaptor. The complete design can be seen in this illustration. 


Brass adaptor


Once everything was installed the thrilling moment of the first steam test came. The engine was serviced as usual and finally the fire in the boiler was lit. The valve of the heating steam line was left open during the steam up process.


In the first minutes nothing happened, but as the water began to warm the first water bubbles flowing through the silicone tube could be observed. The hotter the water in the boiler, the faster will be the flow of water and steam and the heat transfer to the gas tank. Then the moment arrives when the sound of the burner get louder because the steam heated the tank and gas, gas pressure increased and therefore the gas flow through the burner increased.


On a normal day it is now time to close the steam valve in the heating line, as the gas tank is already warm enough. Only occasional short time opening of the valve is needed to keep the steam pressure. On cold days you can leave the valve crack open for a longer time. It is then very important to first check the tank temperature now and then (no overheating is allowed!!!) and listen to the sound of the burner. As longs as it develops a steady sound it is ok. If it get gradually louder, the tank probably gets to warm and you should close the valve a bit.  If it is getting more silent, the gas pressure gradually drops and more heating is required, by opening the valve a little more helps to keep the pressure up.



I have run my Frank S with these modifications for the last year and a half  without any problems. The valve makes it easy to control the heating and the overall performance is much better than before.  Should  you modify your Frank S, you will lose any guarantee from the manufacturer.  Since the locomotive is now 15 years old that may be irrelevant.  However, keep in mind to always run your Gauge 1 live steam locomotive with caution and care.



Appreciation is expressed to Elk Hartmann of Munich, Germany for sharing a record of his experience with photographs in modifying a “Frank S” Locomotive and for allowing us to post this report on the Southern Steam Trains website.  Should you have questions or comments for Elk Hartmann, his email address is <Tedd62@gmx.de>




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