distributor rotor question

Bernie Benz b.benz at charter.net
Mon Dec 8 16:14:58 EST 2003

> From: QSHIPQ at aol.com
> Date: Mon, 8 Dec 2003 12:30:23 EST
> To: pjrose at frontiernet.net
> Cc: mik at info.fundp.ac.be, b.benz at charter.net, 200q20v at audifans.com
> Subject: Re: distributor rotor question
> Doh?!!!!  I call that part of the CBTSB, similar to the UFO debacle, tho this
> one has no such CBTSB documentation attached to it.  Customer bitches loud
> enough, new gear and distributor goes in.
Why would customer bitch?  Few if any plastic gears failed while still under

> Many times, I've seen old invoices
> where it went in AND customer charged.  No question (in my opinion) that audi
> was aware of this problem.  I think the 11mm tip was to design in gear wear
> tolerance.  It's single application design tends to reinforce that claim.
What are you talking about here, Scott.  Makes no sense to me.
> In terms of "how it would 'otherwise' manifest itself?"  By a rod exiting the
> block in a prejudicial method.  I think these plastic gear electrically
> arched pretty early in their service life, but that a bit of arching really
> didn't 
> tax the really strong rods in a stock motor.  Add some software HP into the
> equation, like popcorn...
Ditto this paragraph.  Are you trying to say that you think the plastic
geared 3B/7A distrubutors suffered cross fire to the wrong plug early in
their service life, and that this was a fault of the plastic gear?  I just
don't believe it!
> Every single 20vt 3B I service, has that plastic gear inspection done unless
> documented so already.  I think that was the stupidest idea someone at audi
> had to reinvent the toothbrush.
Nothing basicly wrong with a plastic gear in this application.  In this case
it was poor design and materials selection.

More comment to Phil's post below.
> Scott Justusson
> In a message dated 12/8/2003 11:04:21 AM Central Standard Time,
> pjrose at frontiernet.net writes:
>> ...guess what I'm wondering is: yes, the plastic gear begins to wear and
>> presumably to develop "slop", but how does that show up in engine
>> performance so as as to force Audi/Bosch to develop a metal-geared
>> replacement? My guess is that it was the gears' catastrophic-failure
>> mode ( and not simply the gear wear) which led them to the
>> replacement gear.
IMO and from inspection, the plastic gear does not wear to significantly
increase its gear train backlash.  (It had high backlash to start with,
which was no design problem, until poor servicing allowed the cam drive
system to develop its torsional vibration problems, which greatly agravated
the catastrophic plastic gear failure. A design's deck of falling cards)  If
it did so, the distributor timing mark position would require readjustment
to compensate for this gear tooth wear, which is not the case.  i.e. IMO,
gear tooth wear is not a factor in plastic gear distributor failure.

>> Also, wasn't the narrow (3B) rotor introduced at the _same_ time as
>> the 3B plastic-geared distributor? If your analysis is correct, it
>> would imply that Audi knew from the start that they had a gear-wear
>> problem in their brand-new distributor configuration. Shame on them!
>> Phil

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