[s-cars] AAN Spark Plug Back-out

[QSHIPQ at aol.com]

Having been involved in quite a few repairs and even some legal depositions  
regarding this exact issue, I'll add my two cents and research to this  thread 
(pun intended).  Audi has no TSB regarding the FD5POR plug torque  procedure, 
which means the 22lb/ft torque spec should be used always and  exactly, IMO.  
I use the same procedure many seasoned audi shops use,  torque all to 
22lb/ft.  Then go back 1 by 1 and loosen and retorque to  22lb/ft.  IME/O, an 
overtorqued plug is just as prone to this backing  out problem as an undertorqued 
one.  If any audi tech admitted  using a torque to yield method described below, 
the shop involved  should expect to pay for the repairs if a plug backs out.  
OTOH, if the car  has a bunch of boost mods, don't expect a lot of 
consideration coming your way  either.
 
I've had a couple S cars come to me over the last 15 years with the obvious  
signs of improperly torqued spark plugs.  The first question I ask before I  
even touch the car, is when was the last tune up and where.  On one of my  more 
memorable experiences an S car owner (completely stock) had a  dealer tune up 
and within a month, #4 hammerdrilled the hole  beyond repair.  In my 
deposition, I reiterated the torque spec is key,  explained my procedure, and that the 
damage observed was consistent with  improperly torqued plugs (I don't 
present an over or under theory, both can do  the deed).  And I'll note that the 
tech involved most likely used the T2Y  method described below.  Thankfully, the 
dealer in question did the right  thing, bought the guy a new factory head, 
and replaced the damaged piston as  well.
 
In my 25 years with vw/audis, I have always used M. Gerners method except  
for the 4v/5v motors.  However, even in the old two valve motors using  the 
torque to yield method,  I still find plugs backing out of the head,  the latest 
on a tune up of my kids 86 CGT.  I do not go for antisieze as  that changes the 
conductivity of the plug.  I also don't use oil  either.
 
Turbo motors are more prone to this problem, and IMO, I really think the  
issue is the aluminum threads, steel threaded s-plugs with a massive heat range,  
combined with massive aluminum head heat cycles.  Interesting  too, on all 
the heads I've done steel thread insert repairs on, the  problem goes away.  
 
For high boosted motors that I don't see regularly for maintenance, I  advise 
and teach folks how to use a torque wrench and use it the week after a  track 
event, or every few months.  Amazing the calls I get with the  excitement of 
finding a roque loose plug...
 
My .02
 
Scott J
 
In a message dated 11/14/2007 11:56:48 A.M. Central Daylight Time,  
jgerner2 at kc.rr.com writes:

The  second and most causation related factor is that the factory listed
torque  value for the spark plugs is insufficient. The reason it is
insufficient is  the relative disparity in the “crush load” requirement of
the spark plug  sealing rings. In other words the factory specified spark
plug torque  rating is insufficient to uniformly and consistently crush the
little soft  metal rings that seal the spark plug. (Remember the cyclic
working of this  joint)



Here is what happens; Stock torque spec fails to  sufficiently compress the
seal ring leaving more room for further  compression of the seal ring during
heat cycling of the joint between head  and plug which ends up leaving the
plug loose when it is cold!  This  will eventually let the plug loosen enough
to work its self completely out  over time.







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