The design of the system is such that as soon as the flywheel starts to turn
faster than the starter motor it throws the pinion out of engagement with
the flywheel, unlike the pre-engaged type which remains meshed until you
release the key, and this can happen with just a single cylinder firing just
once and the others not at all, it was not uncommon in the old days to hear
this happen. So your problem could be that the engine isn't properly
catching, rather than the starter dropping out of engagement when it
shouldn't, this shouldn't happen even with slow cranking i.e. due to a weak
battery, cold engine etc. You may be better off looking at why the engine
isn't catching properly i.e. firing just once. OTOH maybe the starter
pinion is only just engaging with the flywheel e.g. because its spiral gear
is dirty or sticky and so the slightest acceleration of the flywheel is
enough to disengage it. With the starter removed you may be able to see
from wear patterns if this is the case, and in any event check that the
pinion is moving smoothly up the spiral gear against the fine coil spring
and back again. The books always said never to lubricate the spiral gear as
it promotes sticking, but I found just thorough cleaning caused the pinion
to fail to engage at all after as little as a few days. An old hand (and
this was in the late 60s) told me to put just a drop of light oil on the
spiral gear after cleaning and work the pinion to distribute it, and I never
had any more problems with it. One drop should leave the surface shiny, no
liquid excess.
PaulH.
----- Original Message -----
> The problem is that upon the very first firing of the engine, the
> gear disengages,
> so that the starter motor continues to spin at much higher RPM,
> but without spinning the engine, so that the engine will not start.
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