With regard to all the recent discussion on Dyak, I have spent some
time looking at the Dyak constructional articles and the drawings
whilst working on the Crab as Martin Barker started that as a
modified Dyak.

I don't believe the drawings add anything that the constructional
articles don't tell you and, in fact, miss some bits out. Things,
from memory, worth noting are:

1. There was an error on the initial frame drawing (distance
between wheel centrelines) that was corrected a few articles later.

2. The cylinders are intended to have a 1/32" fibre shim between
them and the frames. This is only mentioned in the text.

3. Even with the shim I think you will still find that there is a
clash between the crosshead and the driving wheel. On the Crab I
rectified this by reducing the height of the wheel boss from 1/16" to
1/32".

4. There is some discussion that the proportions of the combination
lever could be changed, increasing the distance between the valve rod
and radius rod by 1/32" to improve valve events. Most, however, seem
to run well enough without this.

5. The width of the firebox between the frames is such that it
leaves no clearance. I believe that on Olympiade this is 1/16"
narrower.


As far as castings are concerned, there is no doubt that the Dyak
cylinders can be made from the universal cylinder castings supplied
by the 2.5" association. Des Adeley is having some new wheel
patterns made for the Crab with finer spokes and, as these are
dimensionally identical to those on Dyak, will be fine for the latter
as well.

Hope this helps.

Alex