Operation By Lever When the lever is pulled the wishbone slides to the right. Knob A rotates the crank, which compresses the spring. When the spring goes over centre the points snap into the opposite position. As the wishbone move right the alignment pin disengages from slot S so the wishbone does not rotate as the pin follows an upwards arc.

When the lever is restored the wishbone moves to the left and the alignment pin, pressing against the horn H, rotates the wishbone clockwise so that knob A engages with notch B - ready for the points to be toggled again.

Operation By Trailing Vehicle The points rod compresses the spring. When the spring goes over centre the points snap into the opposite position. As the mechanism reverses the aligment pin moves through an arc and rotates the wishbone clockwise. Knob A engages with notch B. The mechanism is now set so that the next pull of the lever will toggle the points.

Very Brief History Of Wynn-Williams
The following is information that I have received from a mailing list. I have not researched this topic any further.

"The mechanism is known as the Wynn Williams Patent Still-Lever Self Reversing Point Machine.

There were two brothers, Henry Wynn-Williams and Llewellyn Wynn-Williams. Originally they were in partnership manufacturing these items, but then they fell out, and went their separate ways, with one setting up a new company. One side became Henry Williams, now HWD (Henry Williams Darlington), the other was absorbed by Ward's of Sandiacre, now Balfour Beatty Rail Products - a large manufacturer of switch & crossing work."

Still-Lever
This refers to the fact that the lever does not move when the points are trailed.

Patent
I have a photo of a Wynn-Williams casting on which the patent number is readable - 538125. The British Library will snail-mail a copy to me for 25 pounds. As much as I would like a copy I am not sure that I could justify spending NZ$75 on it....... I entered 538125 into the patent search engine and it told me it was not a valid number.

Reversible Points
The Rule Book refers to reversible points, a term I find interesting. The implication is that some points are not reversible! I suspect that the term applies to points that are stable in either position - unlike, say, Gooseneck points where the shunter must sit on the lever to hold the points reversed.

The points have just been reversed by the lever, which is still in the reverse position. The rod at the bottom is the connection to the switch. The end of the sliding plate (which I will call the wishbone) can just be seen abutting the crank.

The spring holds the switch against the stock rail.

A view of the alignment pin. The points have just been reversed by the lever, which is still in the reverse position.

When the lever is restored (to the right) the wishbone will move to to the left and the alignment pin, acting on the lower horn, will rotate the wishbone anti-clockwise.

The lever is being restored (to the right). As the wishbone slides left the alignment pin acts on the lower horn. This raises the right hand side of the wishbone so that the knob engages the upper notch on the crank.

The sliding plate that is the heart of the Wynn-Williams mechanism. I have seen the plate referred to variously as the herringbone plate or the wishbone plate.

The knob on the right engages with a notch in the crank. The lever goes through the triangular hole and the alignment pin fits into the slot on the left. Sorry about the shadow but it was an absolutely brilliant winter's day in Wellington......

Ready for action. The knob on the wishbone is engaged with the notch in the crank. When the lever is pulled (to the left) the wishbone moves to the right, rotating the crank clockwise.

Compare this with the photo on the right, where the mechanism has been turned over.

The alignment pin is in the slot in the wishbone. If the points are trailed the points rod (centre left) will force the mechanism over centre. The alignment pin will move through an arc, rotating the wishbone clockwise so that the knob engages the upper notch on the crank - leaving the mechanism ready for the next pull of the lever.

Wynn-Williams treble leverage two-way spring points mechanism purchased by the NZGR. Photographed at Fletcher siding near Ava. To toggle the points the lever must be pulled away from the split pin.

This maker's information contrasts with the small rivetted plate shown on the right.

A number plate on a points mechanism just north of Gracefield Yard. It reads Balfour Beatty Railway Engineering Montrose St Darlington. Serial 4285. Throw 110mm. Lever Type LT23