Unfortunately, these are only drawn as an assembly with a few dimensions omitted
though it is not a major problem but does require the reader to study it carefully
to ensure it is fully understood.
Valve Block Nut (24)
This is a simple part just a rectangular piece (3/8” x 1/4” x 1/8”) of brass with
a central 5BA hole and being cut from 3/8” x 1/8” only the 1/4” dimension needs finishing
by filing. The tapped hole does though need to be perpendicular to the parts surface
and this can be difficult with such a small component, the following will though
eliminate any likely problem.
Mark out and centre punch the position of the hole but then lap this surface on a
fine file to remove the raised portion of the punch mark. Next, place this, punched
side down, on a flat surface and place an open drilling vice over this and tighten
it. This ensuring as a result that the part is level with the top of the vice's jaws,
drill the part and tap using a guide block as illustrated by Photograph 58. The photograph
should make the principle clear.
Slide Valve (26)
This is a complex little part but most of the requirements are met by the brass casting
as supplied. The valve block nut has to go between the cast in pillars but being
tapered they need filing at their base to permit it to enter fully. Do not remove
too much metal as the nut should be a close sliding fit. More about this part when
finishing is discussed.
Fork End (22)
First make two small steel washers 1/4” diameter with a 2.5mm hole and 1/8” thick,
purpose detailed later. Next place the 1/4” square brass into the four jaw chuck
and set it to run true, drill and tap 5BA 1/4” deep and with the valve rod in the
drill chuck screw the parts very securely together, then shaping the end adjacent
to the rod as per drawing, part off at just over 13/32” long.
Fix the length of brass onto the top slide packing it up to centre height and using
a 1/8” end mill machine the slot to make the fork. Do ensure that you only grip
the part at the end adjacent to the rod otherwise the fork will collapse as you progress
deeper with the slot, see Photograph 59.
Drill and tap the holes in the end of the fork, one being 7BA clear and the other
tapped. Now screw in one of the studs provided and place a washer on either side
securing each with a nut. Use these as a guide to produce the radius by filing. Photograph
60 shows the two valve assemblies I am making, one assembled, the other separate
parts. These are for the 10V and 10H engines.