No more 'ring around the piston'

[erict@cta.com (Eric Thorstenson)]

Andy, a reasonably common failure mode for highly tuned
engines is to burn piston rings. They generally either
turn to carbon or go away completely.

This doesn't seem quite right in your case, as I would
expect the top one to be gone as well.

Have you considered the someone-forgot-to-put-it-there-
in-the-first-place mode of failure?

Eric T.
'64 Autodynamics FV