distributor rotor question

[QSHIPQ at aol.com]

In a message dated 12/8/2003 3:15:12 PM Central Standard Time, 
b.benz at charter.net writes:
> enough, new gear and distributor goes in.
>>Why would customer bitch?  Few if any plastic gears failed while still under
>>warranty.  

Bernie.   A motor shoots a rod out of the block, audi replaces motor.  I've 
seen a couple of service invoices where the distributor was replaced (450USD or 
some such nonsense IMS).  An astute customer would wonder why one switches 
all sorts of components to the "new" motor, but specifically NOT the 
distributor.  I say, IMO, audi knew this was the problem.

> 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.

See above
> 
> 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!

A plastic gear can still be found intact in many of these motors after they 
crossfired.

> 
> 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.

As a former plastics guy, I can't think of any plastic that holds up to motor 
oil heat cycles, especially in any type of gear application.  

>...
>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.

I think high backlash IS the issue, and MORE of it comes as it wears.  Take a 
brand new plastic gear vs one with miles on it.  I don't agree that timing 
adjustment would necessarily be required if the "wear" is an increase in 
backlash.   Lots of sloppy distributors still start without codes, including metal 
geared ones. 

SJ