Machining the Rear Valve Head Cover / Valve Guides
First chuck the part in the lathe using the inside boss. Center the
part as good as possible. Machine the outside boss and surface.
<picture here>
Machine an aluminum plug about 3/4" thick and 1.5" diameter. This needs
to fit in the area between the outside boss and the unmachined valve
guides. Drill and tap for 1/4-20. I sanded two flats on the plug to
assist in tightening.
Next I put a aluminum tube in the lathe, with the inside end plugged,
and a 1/4-20 tapped hole in the center. Machine the end and the bore to
match the outside boss machined above. Make it a close, slip fit. Don't
remove it from the lathe until both Valve Covers are machined.
Thread a threaded rod, long
enough to protrude about 6" past the end of
the fixture, and extend a small amount outside of the spindle. Put a
double nut on the spindle end and tighten. I made a wood plug for the
spindle end so the rod would not flop around. Thread the plug on the
rod and lock on with a nut.
Place the part with the plug
in between the outside boss and the valve
guides, and tighten the rod by turning the double nut at the end of the
spindle.
Continue to draw in the part.
The part is
now tight in the fixture. Not shown in this picture is a relief in the
fixture diameter at the end to make the measuring of the thickness
easier (possible). The photo below has the relief machined.
This shows the part already
machined, except for the valve rod hole.
Finally, I used the same fixture
to mount the Valve Covers in the mill to drill the bolt circle.
Karl Kobel
With the help of Matthew Kobel and Gordon Carlson
(see his
work on http://www.locogear.com/page15.html).