> My ignition seems to be self-advancing. I'll have it timed
> perfectly, then
> after a couple of days it will start pinging a little, so I'll retard it
> slightly with the adjusting nut on the distributor. After doing this a
> couple of times (and remembering on one of these occasions that I had
> adjusted it to the middle big mark on the vacuum advance unit scale), I
> realized that the nut is rotating (through vibration?) in the advance
> direction. What exactly is supposed to prevent this?
There should be a shaped flat spring that goes between the edge of the
thumbwheel and the distributor body. The spring has a ridge that engages
with the knurls on the thumbwheel, so it 'clicks' as you turn it. The
spring is only held in place by the pressure from the thumbwheel, so it's
easy to lose when you remove the advance. The Lucas P/N is 421825.
There should also be a coil spring between the flat side of the thumbwheel
and the housing, it's P/N Lucas 419086. It's primary purpose is to remove
free play from the adjustment, but it would also tend to keep the thumbwheel
from turning under vibration.
I don't know of any source for these springs except for an old distributor
... almost any Lucas with the 'micrometer' timing adjustment will do.
Randall
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