Theoretically there should be some effect from runout, in practice it's
dinky--especially compared to what you'll see with points. I waited a long
time to stick a pertronix on Peyote because I was pretty satisfied with
the dual point Mallory (if it ain't broke...). Then I bent the shaft and
had to use a Lucas. With the points and a Lucas disty, the timing jumped
all over (the shaft was worn, not just bent). I stuck on the Pertronix and
the timing turned rock-solid. Four and one were identical. Going to a new
Lucas distributor didn't change a thing (but it's prettier).
The gap isn't very critical. Changing it doesn't change the timing much,
but as you open it at some point one cylinder will drop out. I suspect an
optical trigger would be even less subject to variation since the window
is at right angles to the rotor, but all in all, these things are pretty
insensitive.
The original point was that you could cure most of the wandering timing
caused by mild distributor runout with a mag trigger because it's way less
sensitive to runout than points.
-----Original Message-----
From: Randall Young [mailto:ryoung@navcomtech.com]
Sent: Thursday, September 18, 2003 3:27 PM
Cc: fot@autox.team.net
Subject: RE: Subject: ignition timing
> Actually it won't. The runout on the distributor makes the timing vary
> because it opens the points sooner on one side of the point cam than
> the other. There's generally not enough runout to change position of
> the lobe relative to the crank. So when you add an electronic trigger
> that doesn't have any sensitivity to point gap then you eliminate the
> variation.
Assuming you're talking about an optical trigger, it will still vary when
the runout is at right angles to the pickup. Not as big an effect, but
there is still an effect.
The magnetic pickups (eg Pertronix) are still sensitive to gap, so they
also vary for that reason.
Randall
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