APART FROM Messrs. Bibby and Henshaw's exquisite little GWR Pannier tank driven by a geared oscillating engine and detailed in the May 2009 Gazette, there seems to have been little published on inside cylinder Gauge O live steamers for many years. In the light of this, members may be interested in a couple of jobs undertaken a while ago, both having twin inside cylinders of similar design.

The first engine was interesting, insofar as it was originally built by E J Cooke in the 1930s . Fitted with an externally fired pot-boiler with water tubes, double-ported piston valve inside cylinders, the valves being similar to the Bassett-Lowke Enterprise/Mogul design and painted dark blue, it was handed to me in pieces and was pretty far gone. The opportunity was taken to fit it with an internally fired boiler and a goods van to hold spirit and water. The original cylinder block was retained and whilst the rebuilt engine functioned after a fashion, both valves blew badly; although when the oil supply was increased to an excessive level, thus temporarily masking the wear, four perfect beats resulted. This situation, which gave the effect of a dog running on three legs, could not be tolerated so a switch to slide valves, which are far less prone to leakage under high pressure, was deemed necessary.

The second engine was a Southern Q1 0-6-0, originally built with a single cylinder but the owner/builder wished it to have two cylinders, an improved water pump and a new boiler, so the decision was taken to undertake both jobs together.

The frames of each engine were ⁷/₈in apart, which decided the basic design; ¹⁵/₁₆ in would have been better, 1in better still, but such constraints are placed in our path to be overcome. As I wished to avoid angled connections for the steam and exhaust, the port face of the cylinders would have to be flat whilst the bores needed to be at an angle to miss the front axles. The valves are on top as, in the tank, there was no room to fit them below owing to the small wheels and the full size Q1 had valves on top in any event. With the limited amount of space between the frames, there would have also been difficulty in drilling an adequately sized exhaust passage between the bores.

Each block was mostly four-jaw chuck work. They were initially squared off to overall length, width and height using the rear of the chuck as a register. Nice, shiny and square pieces of bronze are a joy to behold. The bore centres were marked out using the drilling machine table as a surface plate and with a small height gauge that I picked up years ago at an auto-jumble. With the centres established, they were centre-popped with a punch and one was set to run truly in the four-jaw using a clock gauge. Before I had this useful weapon, I found that, using the eye together with a tailstock centre, it was possible to get centre pops running reasonably accurately but, with a clock gauge it is feasible to set centre pops to virtually 100% accuracy, a great help later on.

Once the centre pop was running truly the bore was centred with a No. 1 centre drill, drilled through ⅛in and followed up ⁹∕32 in. With a small boring tool, it was opened out until a ⁵/₁₆ in reamer entered to about a third of its length. Using the lowest back gear speed on the lathe and a brush full of heavy motor oil, the reamer was pushed through with the tailstock. I find that 20/50 oil is an excellent lubricant for reaming as it seems to damp out the vibration that can sometimes affect the operation. The reamer was kept moving at all times on both the ‘in’ and ‘out’ passes and that was the first bore finished subject to lapping. The process was duly repeated for the second bore. Before removing the block from the chuck, a very fine skim was taken off the projecting part to true this up, as it forms the register for the rear cylinder covers and must be exactly at 90 degrees to the bores. The front isn't so important and was left as originally squared off.

As usual O rings were to be used on the pistons and to give these as easy a life as possible, the bores needed to be polished to a reasonably high finish. This was accomplished by lapping. There have been many long and erudite articles written about this process but for the component in hand a piece of hardwood turned to a wring fit (ie with no slack) in the bores was all that was necessary. The fit required for the lap is sufficiently tight to 'squeak' when pushed into the bore but still rotatable without threatening to fracture the wood. With the lathe running at its lowest open speed (ie driven with no intermediate gears) and having first put a piece of cloth over the bed to catch any stray drops, the lap was charged with liquid metal polish. One cylinder bore was run on to the lap and carefully worked up and down keeping it constantly on the move to avoid bell-mouthing. When the lap ran freely, the cylinder was removed and a piece of soft cloth run down the bore to clean off the residue. On inspection, the bore was found to have a highly polished finish. All very satisfactory.

The process was repeated for the other bore but the lap was found to have worn a little slack, so the end was drilled and a wood screw inserted to expand it slightly and restore its cutting ability. Health and Safety hint. If you try lapping and I hope you will, the component can become uncomfortably hot to hold in the bare hand, so an old gardening glove is a useful adjunct to the operation. With the basic machining of the blocks out of the way, consideration was given to the required angle of the bores in the frames and the amount to be removed to secure a flat top to the port face. This was relatively easy to achieve by clamping the block against the frame so that the centres of the bores were clear of the front axle and in line with the crank axle bearings. A level was then taken across the top of the block and machined flat to form the port face. Another job for the milling machine or vertical slide. The angles of inclination were different for each engine but the procedure was common to both.

The steam ports were cut with a No. 1 centre drill which has a 3/64 in diameter point. These, when run fast, act as a first-rate milling cutter. The exhaust ports were machined with a 3/32 in slot drill. The steam passages were drilled No. 51, care being taken to compensate for the differing angles of the passages caused by the angled bores and flat port faces. The exhaust passages were simpler to drill, being all in one plane, but some care was necessary to ensure that the No. 45 drill did not break when entering the 7/64in diameter riser. This completed the block ready for the cylinder covers and steam chest. I'm afraid that I do seem to have gone on somewhat about cylinder block construction, but it is the heart of any locomotive and due care in its machining will be repaid by ease in lining up connecting rods and motion and a long and trouble-free service life.

The steam chests were machined from ¼ x 1in brass bar, the O ring gland housings being silver soldered into one end and the valve guide spindles into the other. These items were turned from drawn bronze which has good wearing characteristics. As the glands are relatively prominent, the covers were attached using four per engine of my rapidly dwindling stock of 14BA hexagon bolts. Nowadays, they seem to be unobtainable unless someone out there knows differently. The slide valves were made in two parts as it simplifies the process of cutting the cavities. The working surfaces in which the cavities were cut were made from small pieces of 1/16 in thick phosphor-bronze, again a hard-wearing material.

The cavities were formed by initially drilling a ⁵/32in hole in the blank and opening it out to size with a square needle file. The drive block was formed from 1/8 in brass, the two items being silver soldered together. Slots for the drive nut and valve rod were then milled out, great care being taken to ensure good working fits for both items. The valve should be free to float on the nut and rod but should not be slack or the valve events will be upset. To true the working surfaces of the valves, they were rubbed gently on a sheet of fine emery cloth held on the drilling machine table.

The other components that it was vital to get spot on were the crankshafts. Over the years there have been a number of methods of making crankshafts described in the model railway and engineering press, all of them sound, but in this application, as it was necessary to include slip eccentrics on the centre section, a two-part type that screws together was used. This design was employed with great success by the late Clarry Edwards, so that is recommendation enough.

The four web blanks were cut from 3/8 x 1/16 in mild steel, soft soldered together, squared off and, to ensure accuracy, the 3/16 in shaft holes were drilled in the lathe using the four-jaw chuck. The ends were rounded off using a ¼in milling cutter in the three-jaw, with the blanks threaded on to a piece of 3/16 in rod mounted at centre height in the tool post. A toolmaker’s clamp was attached to the blanks to use as a lever, and great care exercised to take small cuts as the blanks were rotated against the cutter. Too heavy a cut would have resulted in the cutter digging in with disastrous results all round. With the ends nicely rounded off, the blanks were melted apart and all traces of soft solder removed.

The eccentric stop pin operating flats were then machined on the inner crank webs and the two halves assembled and silver soldered before final machining. The centre part of one of the halves was turned down to ⅛in diameter and screwed 5BA and the other half drilled No. 38 and tapped 5BA to suit the male half. A 3/16in collet was used to hold the axle ends as, naturally, the more accurate the machining, the truer the finished axle will run. The centre parts of the axle opposite the crankpins were then carefully cut away and the two halves screwed together.

If the crankpins are not at 90 degrees to each other, a tiny touch off the female centre portion will correct matters. But I was lucky and did not have to do any surgery of this type. The completed crankshafts were spun by hand in the lathe against a clock gauge and were found to be two 0.002in out at the far end which was a good result as far as I was concerned. Time for a beer!

Eccentric centres were turned from silver steel which is a bit over the top for the purpose but, as it was to hand it was used, for, as I am sure you will have gathered by now, it was the intention to make the engines as wear-proof as possible. They were machined using the Eddie Cooke method with a flange on one side to hold the strap in place, the crank webs acting as a barrier to hold the other side. The throw was ⁵/64 in to provide a valve travel of ⁵/32 in. The straps were made from ⅛ x ⁹/16 in steel plate, the two halves being soldered together prior to being bored out ⁷/16in for the sheaves and subsequently filed to shape. The drive to the eccentric rods is taken from the top of the straps to provide the necessary height to avoid undue angularity of the rods. Whilst I do recall seeing something similar in an old copy of Model Engineer, this idea approximates to that used in the Gauge 1 'Dee' design, an excellent engine, well worth consideration if you are into broad gauge.

The connecting rods were hacksawed and filed from 1/16in gauge plate and fitted with mild steel big ends, silver soldered in place. Mild steel is perfectly suitable to use in O Gauge and, if kept clean and well lubricated, seems to resist wear better than the normally specified bronze or gunmetal big ends. Cast iron is also very good for this application but can be difficult to silver solder to a steel con rod. The con rods were then assembled on the cranks and the final rod lengths determined by setting the pistons on full stroke less ¹/64 in, marking off the gudgeon pin centres on the rod blanks and drilling appropriately. The little ends were shaped using the same method as the crank webs. Hardening was then required to ensure longevity and this is relatively simple to carry out. The eyes of the little ends were heated to bright red, the colour of boiled carrots is about right, and then plunged vertically into heavily salted cold water which produces a better hardening effect than plain water.

After cleaning up, the eyes were tempered by reheating until they were a light straw colour and plunging into oil. The gudgeon pins were dealt with similarly. The fit to be aimed at with hardened pins and eyes is to get the parts to fit closely with a slightly 'scratchy' feel when the assembly is operated dry. This is something that is better experienced than described. The motion plates were slightly tricky as they needed to clear the eccentric rods, support the guide bars and valve rods and accommodate the crosshead driven pumps. However, a little milling together with a few hours scraping away with needle files produced the necessary articles from ¼in steel plate.

The centre flue boilers fitted to the engines are excellent steam producers as they provide a large amount of heating surface combined with a reasonable firebox volume to assist flame stability. However, the water capacity is limited, thus necessitating an engine-driven pump to ensure continuous running if required. As indicated above, there being no room to accommodate a conventional axle-driven pump, recourse was had to the crosshead-driven variety. In my experience, one of the chief problems with pumps is the need to arrange both the layout and supply pipes in such a manner as to preclude air locks as far as possible. To this end it proved feasible to ensure that the pumps on both engines could be fully flooded from the hand pumps which were located in the tender on the Q1 and in the bunker on the tank. There are several designs of crosshead pumps about. These range from those involving close fitting rams with the valve column on the end, rather like an elongated axle pump of normal design, to those with clearance round the ram and the valve column at the side. A quick tip with regard to limiting any propensity to develop air locks is, before steaming the engine, to make sure that the axle pump ram is fully home whilst priming the system with the hand pump.

To minimise the width of the pumps, the valves were arranged in line with the output valve at the highest point. The rams are ¹/16in diameter running in a ³/32 in bore to provide clearance to enable them to be fully flooded. The rams are, of course, a close fit in the gland housings, the glands being sealed with O rings. The valves incorporate ¹/16 in stainless steel balls with 0.010in lift. The seats are burnished with a spare ball soldered to a small brass rod. This is spun in the lathe at the lowest open speed and with a smear of oil on the seating, is pressed against it firmly for a few seconds. This seems to provide a much truer seat than the accepted method of tapping a spare ball on the seat with a hammer and drift. John Shawe put me on to this trick and I can thoroughly endorse it.

The pump bodies were formed from ¼in diameter bronze for durability with the glands machined flat at the sides to fit into the bare 3/16 in space, which was all that was available between the crossheads. The glands were sealed with ¹/16in bore x ⅛in OD silicone O rings which are a standard size. Because of the limited flange area, the gland retaining screws had to be 16BA. This is the smallest thread that I have the equipment to produce and before marking out the cover it was necessary to give my glasses a good polish. The drive gear is quite simple, being a U- shaped lug that fits over a bobbin screwed to a bracket attached to one of the crossheads. Both lug and bobbin are made from silver steel and hardened for longevity. The shape of the lug enables it to slide on the bobbin and thus accommodate itself to any slight discrepancies in alignment.

Several of these pumps have been constructed over the years and have proved quite effective, especially when used together with check valves fitted with O rings. These have the advantage that the higher the pressure in the boiler, the better the valve seals. Anyway, that's the theory.

Lubrication is extremely important in these small cylinders, and whilst I have seen small mechanical lubricators, the hydrostatic type is certainly easier to build as they have no close-fitting moving parts and, with care, can be made quite reliable.

The shape of the oil tank is fairly immaterial and it can be located at any convenient point within the structure of the locomotive. That for the tank engine is sited inside the right-hand dummy side tank and is charged through the hinged lid of the water filler, whilst that for the Q1 lurks under the cab floor. Although the oil pipe runs are relatively long, a steam feed from the boiler via a needle valve ensures that the oil starts feeding at the commencement of a run. Usually, displacement action will keep the oil flowing, but if the tell-tale ring of oil round the chimney top dries up, a quick burst of boiler steam will soon restore it. The briefest opening and closing of the valve will suffice. On some of my engines a metering valve has been fitted to the oil supply. The intention of this is to even the flow of oil to the cylinders, but some care and patience is needed to achieve the right setting, as I have found that these small valves with a 10BA stem are fickle and occasionally unpredictable items. Of course, the running shed will always criticise the design office!

This about completed the mechanics of both jobs, so it was time for assembly. The completed cylinders, steam chests and guide bars were erected in the frames together with the motion plates, valves, valve rods and crossheads. The wheels were quartered using a jig and pressed on, not forgetting to jam two pieces of ⅛ in plate between the crank webs to prevent them closing up under pressure. The conrods were installed together with the pump drives and the engines turned over by hand.

It would be nice to say that each chassis turned over smoothly. Not so; on the tank, the left hand piston hit the front cover just before dead centre necessitating the piston rod to be slightly shortened. On the Q1, the opposite happened, with the right hand piston hitting the rear cover. This required the rod to be lengthened. A couple of turns on the threaded piston rod effected the necessary adjustment and we were home and dry.

With the steam chest covers removed, the port openings were equalised by slackening the clamp screws on the valve crossheads and moving the valve rods appropriately. The flats on the crank webs automatically took care of the valve setting. On replacing and jointing the covers with Loctite 572 (expensive but good), the moment of truth was looming. A quick squirt of oil down the steam inlets and the airline was applied to each chassis. I am pleased to report that both chassis turned over well and evenly, both in forward and reverse. The tank was a bit ‘rattly’ owing to the re-use of E J Cooke's original coupling rods and axle bushes which were somewhat worn, but I suppose that it all adds to the character.

Both engines were completed in due course, the Q1 with a new boiler and a few alterations to the tender. Fully painted, it made its debut at Telford and is, I understand, continuing to perform in a satisfactory manner. The tank will haul to the limit of its adhesion and keep going for about half an hour non-stop with a rather rollicking gait. I have had no ghostly visitations to the workshop so I must assume that Eddie Cooke’s shade is reasonably happy with the result.

In conclusion, and by now I have probably tried your patience to the point where you have yawned and turned to Mailvan, I can confirm that the above was written with a reasonable amount of confidence, as I have also completed the rebuild of a small LNWR 4-6-0. The cylinder arrangement is exactly the same as described above and it runs well. Accordingly, there would seem to be no reason why you should not be able to bring to life your own Cardean climbing Beattock with the down ‘Corridor’ or a GCR Sam Fay slogging up to Woodhead with a Manchester express. All the right noises and smells too!