Backlash was Distributor

[Bernie Benz]

From: SuffolkD at aol.com
Date: Tue, 9 Dec 2003 00:52:57 EST
To: 200q20v at audifans.com, b.benz at charter.net, QSHIPQ at aol.com
Subject: Re: Backlash was Distributor



I ask to this quote posted here and below Bernie:
"inasmuch as the driving cam gear is always doing so and the backlash is out
of the loop.  Only if the cam drive system has a low frequency resonant
torsional vibration................"

What about lift/close throttle after high RPM?
Wouldn't the "driving cam gear" now backlash? as taken out of your example
quoted above?
Yes, during rapidly decelerating engine speeds, closed throttle, clutch in,
any back lash could cause the dist to further advance for this period, but
the ECU is controling spark timing, not the distributor.  If distributor
timing gets far enough off the ECU will start to shut down.  But IMO the
back lash of a good plastic gear (no tooth root cracking or missing teeth)
is negligable relative to this far out argument.

The spark from the rotor tip will always take the path of lowest resistance,
usually the shortest distance to a cap contact point.  Distributors are not
sealed and often vented to disipate ionized air that can cause the lowest
resistance path not to be the shortest.  IMO this is the more likely cause
of those reported (?) cases of destructive cross fire.

As I have said before, if you wish to convince youself of what is  the
shortest distance to a cap contact point:

Thanks Mihnea,

With this info on max chipped advance, the "narrow minded" could lay out to
scale on paper the plan view of the dist cap with TDC on the #1 plug
centered on the rotor width (is this correct?) and dial in the max advance
with the two different rotor widths, and see if the max rotor position
remains closer to the #1 pin than to the ajacent pin on the wider tip.  If
so, not to worry.

Bernie
 

My guess (from the education ya' all have provided me) is that this
"backlash" during upshift or the like, could create the
environment/situation for "cross fire " in a High HP/RPM 3B.

-Scott by BOSTON.... yes, I realize the Scott below is "QshipQ".  Just
jumping in. 

In a message dated 12/8/2003 11:25:39 PM Eastern Standard Time,
200q20v-request at audifans.com writes:
Scott, inasmuch as the distributor timing marks must be in alignment within
a degree or so, any appreciable wear on the driven side of the plastic gear
would alter this static timing adjustment.  IMO, such wear is not the case.
Excessive dist gear backlash is normally no problem, inasmuch as the driving
cam gear is always doing so and the backlash is out of the loop.  Only if
the cam drive system has a low frequency resonant torsional vibration (the
20V dist rattle) will the dist backlash be a factor in instantaneous dist.
timing. 

Bernie