[s-cars] AAN Sparkplugs from 94 Quattro

[djdawson2 at aol.com]

Agreed 100%.  It is very obvious when the "crush" occurs.  I have always tightened based on this feel as well, and I've never had one come loose.



Nonetheless, I will never install a Bosch plug in these engines again.  I have had too many of them drop the electrode, and one of them dropped the entire ceramic insulator.



Dave


-----Original Message-----
From: Jeff Gerner <jgerner2 at kc.rr.com>
To: s-car-list at audifans.com
Sent: Wed, 14 Nov 2007 9:36 am
Subject: [s-cars] AAN Sparkplugs from 94 Quattro




Hello guys – this is my first EVER post on this site so I am “breaking my
herry” in order to shed some light on this sparkplug debate. I am a
ifelong auto tech and engine builder as well as the owner of a very fast 94
4 that I have “done all the work on” etc. I am no kid either at 54 years.
 
Anyway, on to the subject; Rule # 1. Properly tightened – notice I did not
ay torqued – spark plugs, just like properly tightened wheel lug nuts /
tuds, don’t come out. Period!
 
 The spark plug loosening problem happens for two reasons; First is the
ighly dissimilar “growth rate” of aluminum vs. steel / iron as in the
ylinder head spark plug interface – the aluminum cyl head grows or swells
ore in dimension (under extreme heat) than does the spark plug shell. This
auses “cyclic working” of this joint between plug and head as the engine
ycles repeatedly from cold to very hot.  This problem is exacerbated by the
ather extreme cylinder pressures and temperatures associated with high
oost engines.
 
 The second and most causation related factor is that the factory listed
orque value for the spark plugs is insufficient. The reason it is
nsufficient is the relative disparity in the “crush load” requirement of
he spark plug sealing rings. In other words the factory specified spark
lug torque rating is insufficient to uniformly and consistently crush the
ittle soft metal rings that seal the spark plug. (Remember the cyclic
orking of this joint)
 
Here is what happens; Stock torque spec fails to sufficiently compress the
eal ring leaving more room for further compression of the seal ring during
eat cycling of the joint between head and plug which ends up leaving the
lug loose when it is cold!  This will eventually let the plug loosen enough
o work its self completely out over time.
 
The fix; When installing new plugs VERY lightly oil the top half of the
hreads and the seal ring to aid the seal in crushing and then tighten the
lug until you feel the seal compress and the plug become fully tightened.
ou will feel the initial resistance of the seal meeting the head surface
nd you will feel the crushing of the seal ring as you slowly increase the
orque. You will know when the plug is “properly tight” when the resistance
o tightening suddenly increases. If you have any “feel” for these type of
hings you will not have any trouble doing this. If you don’t trust yourself
ust have someone who is a full time wrench do the job.
 
Note; some people will screen “blasphemy – must use torque wrench when
nstalling plugs”  The truth is that only 1 in 50 experienced techs use a
orque wrench to install spark plugs – they don’t need it because they can
eel when the plug is tight enough to stay in while still not being over
ight.
 
Hope this helps. 

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hecked by AVG Free Edition. 
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:22 PM

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