You can also find various speedy valve gear comments via the online index

The valve issue was in the postbag

e.g. From ME no 3200

SIR,—As I am about to begin
work on the valve gear of the 5in.
gauge Speedy I was interested to
read the letters of Mr Robertson
and Mr Smith in Postbag.
The combination lever propor-
tions given in the working drawings
with a piston stroke of 2-1/8 in. give
a valve movement of only 0.145 in.,
and are not, therefore, correct for
the given valve lap of 5/32in.
(0.15625 in.), as this would leave the
valve blind by 0.011 at the end of
the piston stroke, consequently pro-
viding no lead.
It would seem that the simplest
modi¿cation to correct this error

would be to retain the existing com-
bination lever proportions and re-
duce the lap on the valve from
5/32in. to 1/8in. This would provide
a lead of 0.02. If a lead of 0.02 in.
is considered too large, a lap of
1/8in. plus 0.01 in. could be used.
I would be grateful for any
further information or comments.
Shaldon, R. E. VOKE.
Devon.
[While we agree that the existing
combination lever proportions could
be used if the lap is reduced to
0.125 in. with 0.020 in lead, we think
that you will obtain better results
by using the original 0.156 in. lap,
with, say, 0.015 in. lead. The com-
bination lever could then be made

0.40 in. and 2.485 in., the second
dimension being taken, of course,
from the upper pinhole. The drop-
link would also have to be shortened
a little to avoid too much angularity
of the anchor (or union) link.
We understand that the main
trouble with the SPEEDY valve gear
was insufficient valve travel. We do
not see why you should not obtain
a full gear valve travel of 11/16 in. by
increasing the throw of the return
crank (and its length) and by in-
creasing the movement of the re-
versing arm, as long as the total
angular swing of the expansion link
does not exceed about 45 deg.-
EDITOR.]

Edited By Ady1 on 05/08/2014 11:06:21