Classic UK Minitrix Models  -  Britannia
Valve Rods

The valve gear on the Britannia is very distinctive.  It has thicker con rods, less prone to bending, and the valve mechanism is much simpler than that on the Mallard, Scotsman, 2MTs and 9Fs.  The slider is metal, and this only supports the piston and the main con-rod from the centre wheel.  There is no additional valve mechanism.

Also, the main crank on the centre wheel is metal, not plastic.  In other words, there is very little here that can break.

Note the thickness of the rod which connects the drive wheels.  A massive finger, but actually it is easier to get the screw turning using a finger on top of the head than it is using tools.  There is much more 'feel'.  It only requires a small turn to get it started, after which a 2mm hex socket driver can be used.  Post a message if you wish to know where to get one of these from.
This had me confused when I first tried to get the valve gear into the cylinder housing.  Note that there are TWO round holes.  The piston rod goes into the lower one.  There is a rectangular hole in between the two circular holes, into which one of the rails fits. This one is difficult to see, even with a magnifying glass, but it IS there.    Here, both rails have been inserted.  The main con rod to the centre wheel slides onto the piston pin, and the open end of the pin can then be eased into the lower hole, after which the whole assemble can be pushed home into the cylinder housing.  The upper round hole is not used.
The Britannia (bottom) and Scotsman (top) shown in the same photo to compare the two types of valve mechanism.  On the Scotsman, the extra lug on the plastic slider makes this component very vulnerable to damage.  The plastic crank on the centre wheel is also very fragile.  The Britannia, on the other hand, has no such issues.

Maintaining Classic UK Minitrix Locos
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