Steve,
I worked on a Ford Cortina 1600 that had a problem with valve lash
jumping all over the place: although the camshaft is retained in a different
fashion, it had worn its thrust surfaces (both the cam shaft itself and the
retainer) and it was walking fore and aft in the block. Cam lobes are ground
slightly off of flat to encourage the tappets to rotate, and as long as the
cam stays put, the lash stays the same. If the cam travels, this problem
will appear.
I disassembled one Rootes engine years ago that had a shattered
thrust plate, although I have no idea if or how it ran. It is possible that
your camshaft is in fact moving back and forth, causing unstable valve lash
readings, and it walked far enough to loose contact/misalign with the oil
pump drive gear, and it consequently failed. There isn't much extra room in
the timing cover for fore/aft motion, but a quarter inch would be
possible...and extreme!
I still think you should check under the breaker-plate in the
distributor to see if a small nut or washer found its way in there, before
you use that distributor again.
Jim Leach, Seattle
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