By Ken Best
Pssst – Want to know a secret?
No doubt, by now, most of you will be familiar with my thirty years old “Super Mamod”, but not many have actually been able to have a close look at what goes on beneath that great blue body. Therefore at the suggestion of our esteemed Heritage Officer, Derek Wiggins, I will attempt to describe her workings, without hopefully boring you with the obvious.
The loco is actually three separate units :-
First we have the Mamod with shortened frames and not much bodywork. Next there is the meths tank/burner, followed by the American outline body.
To get “Miracle” up and running is simply a matter of oiling and watering the Mamod, filling the meths tank, lighting it and then lowering the Mamod over the burner section until a clip on the front of the tank can be pushed forward over the rear frame spacer.
Finally, the body is lowered over the loco so that the Mamod’s chimney sits inside that of the body and the rear of the meths tank is locked in place by the bottom rear edge of the cab.
Now that you know how she goes together, lets see how it all works.
First, those great powerful looking cylinders. – Well, of course they are only dummies, but you had already guessed that, hadn’t you?
They are nothing more than covers, concealing the real (and rather ordinary) Mamod cylinders. The crossheads, slide bars and connecting rods are also dummies and the job of moving the loco is still left to the original Mamod parts, with the speed, forward and reverse control still operated by means of the original lever on the front of the loco.
Look closely at the above and next two photos and you will see what I mean.
Now lets see where all that power comes from.
The workings of the Mamod are absolutely standard, except for the safety valve, the original 12psi having been replaced by one of 25 psi. Also a displacement oiler has been fitted, plus a water top-up valve and the sight glass hole in the rear of the boiler has been covered with a brass plate to remove any chance of leakage. (I use a stop watch to time each run so that I know when to add water to the boiler). The meths tank holds approximately 90ml and with the three wick burner and water top-up system, I estimate that she should have a running time of about an hour and a half – although to date, I have not actually run her on a full tank of meths due to the fact that my garden line is 45mm, not 32mm and my O gauge circular test track is on a board measuring only 6×4 feet, making me rather bored and also rather dizzy after half an hour or so.
Finally the body.
The next photo shows the curved heat-shield with four holes in it. Reading from left to right, they are for the chimney, the water top-up valve, steam dome and safety valve.
On either side of the heat-shield is a flat metal strip which is used to position and steady the body by resting on top of the original Mamod side tanks.
Sitting inside hole number two is a brass tube which allows the water top-up bottle to be used when the body is in place. The tube runs directly from the front sand dome on top of the body and positions exactly over the water top-up valve once the body has been placed over the Mamod. Access to the tube is gained by lifting the hinged lid of the sand dome.
Running from hole number four is an “S” shaped tube which finishes under the small brass pipe in the middle of the steam dome on top of the body. This allows the escaping steam to be released from a more appropriate place, thus giving a better visual effect.
Finally, moving to the rear of the cab, you can see the position of the two AA batteries which power the front and rear lights via a switch in the coal bunker. Incidentally, the bulbs used are the original 2..5 volt, old style, large torch bulbs which I fitted thirty years ago – and they are still going strong!
And that’s how “Miracle” works!
Now you know the thirty year old secret – but please, keep it to yourself.