A 5 in. Gauge Bulleid Pacific.
An article by Mr. A. R. W. Crowhurst :
originally in Model Engineer of 7 March 1975;
re-published courtesy of Tony Crowhurst & M.E.
All non-digital b&w photographs taken by Tony Crowhurst.
A stunning 5" gauge model of a West Country class Locomotive;
built by the late R. Cushing with chain drive valve gear, steam reverse, multiple jet blast pipe, etc.
Having built a 3 1/2" gauge pacific, Mr R. Cushing, Kentish enthusiast, decided that a loco suitable for children to drive would be an advantage, as the railway in his garden naturally attracts them.
Several ideas came to mind but it was decided that a steam outline would be more appealing, and that a "spam can" would enable all motors, etc. to be housed inside the air smoothed casing (it was to be electric drive).
Drawings were obtained from Eastleigh drawing office and a start made on the design work.
However, it was not long before the crank axle was made "just to see what it would look like in 5 in. gauge".
This really started thinking in detail, and after more full size drawings were obtained, the frames for a 5 in. live steam Bulleid were cut out and all thoughts of electric locos. abandoned.
The design was thought out as the work proceeded, although the full size drawings were used to scale down the parts.
A crank axle was fabricated from silver steel and gauge plate, the journals are 3/4 in. diameter and webs 1/2" thick.
In order that the loco can negotiate 22ft radius curves, a litle extra side play was put into the axle boxes and bogie.
The valve gear was scaled directly even to port sizes, travel etc.
Blast pipe orifices were also scaled directly and despite various critics, the engine is a very free runner and extremely powerful.
Driving wheel patterns were made up, and the wheels cast in close grained iron, as are the cylinders.
A small deviation from full size wheels was made, namely omitting a recess which after a visit to Nine Elms depot was found to be full of dirt and flush with the wheel anyway !
It would take a practised eye to spot the difference.
The reason this was done was to save on casting charges which would have been £16.00 per wheel !
Cylinder lubrication caused some long thought, as first a six ram pump with ball valves, then mitre valves was tried, without complete success.
However, the LBSC design was eventually tried, but with neoprene seats for the valves, and this will pump up to 300 psi, although it is set for somewhat less; the ram is 1/4 in. dia x 1/4 in. stroke.
Chain drive is used as per full size except that instead of morse inverted tooth chain, an 8mm roller type is employed.
All parts of the valve gear are hardened out to minimise wear.
The valve gear 3-throw crank shaft was machined from solid bar.
The piston rod glands are packed with "Chevron" packing, supplied by James Walker, Woking, it being their smallest size in this type of packing.
The boiler is of steel construction, welded from 1/8 in. steel plate to EN2A specification.
The tube plates and back head are 3/16 in. steel.
Tubes are 23 in number, 3/8 in. bore copper, silver soldered in.
Five superheater flues are fitted of 3/4 in. bore.
Syphons are fitted in a combustion chamber, these being 6 in number, three either side and 3/4 in. dia., not unlike the 5 in. Britannia design.
Stays of which there are 150, were screwed into very tight threaded holes and "Loctite" used to finally seal them and nuts used on the inside of the fire box.
Three safety valves are fitted and set for 90 p.s.i. although the boiler is passed for 200 p.s.i.
The regulator is the LBSC slide type, as the full size double beat one gave some trouble and was not very reliable in service.
Main steam pipes in the smoke box are phosphor bronze convolute type, so making connections easy and enabling the boiler to be removed in only 10 minutes.
Boiler feed is by twin injectors on the right hand side.
On the back head are the usual fittings and also axle box oil lubrication boxes.
In order that work can be carried out on the outside of the boiler, and the boiler easily removed, the outer casing and cab are all one piece, so a few minutes' work has this removed complete.
Working leaf springs carry the engine, and these are of spring steel throughout, with correct rolled eyes with phosphor bronze bushes.
Each spring takes 40 lbs weight, the axle being about 80 lbs.
There are 40 leaves to each spring !
The chassis has the correct number of stretchers and lightening holes and a gear oil pump to lubricate the valve gear which is enclosed in the famous oil bath.
This has been given a great deal of thought so that no oil leaks from it, and even after weeks of standing no oil is found to have dripped onto the bench.
It is easily removeable for maintenance.
Reverse is by steam, but like the full size it can be a bit too free when warm, so the engine is usually set in forward gear and left there, although a skilled driver is able to use it to advantage.
Working leaf springs are used on the tender which has a brass tank.
The axle boxes, however, are of an experimental material - polypenco nylotron - which needs no lubrication, although some is provided by oil-can.
This gives a very free vehicle, as if on ball races.
A hand brake is fitted and the vacuum cylinders as mentioned earlier.
Steam brakes stop the engine very swiftly, but the vacuum brakes are dummy, although the tender brake cylinders are operable as and when an ejector is fitted.
Over 6,000 hours work went into the engine, of which 3,000 were problem solving.
This was spread over 6 years, the loco being completed in mid 1973.
The engine dimensions are :-
Length over buffers - 6 feet.
Height - 14 inches.
Width - 9 1/2 inches.
Weight - 4 cwt total working order.
Cylinders - 1 9/16 in. bore x 2 1/8 in. stroke.
Grate area - 42 sq. ins.
When first completed, Mr Cushing found it difficult to drive; however, a visit from a "full size" driver, Alan Wilton of Nine Elms, soon put things right.
It is, Wilton says, just like the being on a real loco in every way, and after umpteen laps of the dimunitutive track at Mr. Cushing's home, he finally got off and said "Lovely, Woking in 62 !"
Other drivers have driven the engine including the famous Bert Hooker, who fired on No. 34004 in the Exchange Trials of 1948.
His remarks were that if you shut your eyes you can't tell the difference !