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.

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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.


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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.


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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.

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Continue to draw in the part.

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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.

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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).