This past weekend I fixed the left hand vent on the XK120. It had been
held open or shut with a bent piece of rigid wire, but the design of
the mechanism was quite elegant.
I seems there are two hollow tubes, the forward one fitting over the
rearward one and inside these tubes is a strong or semi-strong spring
pushing outward against the two fixed ends. This spring compresses
midway between open and shut and that is what you are feeling when you
work the vent lever.
Somehow I chanced on this solution, seeing I had thought the spring
would pull against the ends, and kept cutting the spring shorter and
shorter to get more “pull”. By the time I finally realized the spring
should be pushing out, I had cut it too far to do much good. It seems
that a pin was originally placed inside the outer tube to be the
forward push point, but I used a cotter pin there.
- Tom Finden