[s-cars] AAN Sparkplugs from 94 Quattro

[Mark Strangways]

[stepping back from the internet now, as it is about to explode]

They like torque wrenches around here...
And don't even mention AS compound..

;-)  [big smiley]

Mark
----- Original Message ----- 
From: "Jeff Gerner" <jgerner2 at kc.rr.com>
To: <s-car-list at audifans.com>
Sent: Wednesday, November 14, 2007 11:36 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
> cherry” in order to shed some light on this sparkplug debate. I am a
> lifelong auto tech and engine builder as well as the owner of a very fast 
> 94
> S4 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
> say torqued – spark plugs, just like properly tightened wheel lug nuts /
> studs, don’t come out. Period!
>
>
>
> The spark plug loosening problem happens for two reasons; First is the
> highly dissimilar “growth rate” of aluminum vs. steel / iron as in the
> cylinder head spark plug interface – the aluminum cyl head grows or swells
> more in dimension (under extreme heat) than does the spark plug shell. 
> This
> causes “cyclic working” of this joint between plug and head as the engine
> cycles repeatedly from cold to very hot.  This problem is exacerbated by 
> the
> rather extreme cylinder pressures and temperatures associated with high
> boost engines.
>
>
>
> 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.
>
>
>
> The fix; When installing new plugs VERY lightly oil the top half of the
> threads and the seal ring to aid the seal in crushing and then tighten the
> plug until you feel the seal compress and the plug become fully tightened.
> You will feel the initial resistance of the seal meeting the head surface
> and you will feel the crushing of the seal ring as you slowly increase the
> torque. You will know when the plug is “properly tight” when the 
> resistance
> to tightening suddenly increases. If you have any “feel” for these type of
> things you will not have any trouble doing this. If you don’t trust 
> yourself
> just have someone who is a full time wrench do the job.
>
>
>
> Note; some people will screen “blasphemy – must use torque wrench when
> installing plugs”  The truth is that only 1 in 50 experienced techs use a
> torque wrench to install spark plugs – they don’t need it because they can
> feel when the plug is tight enough to stay in while still not being over
> tight.
>
>
>
> Hope this helps.
>
>
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> 11/13/2007
> 9:22 PM
>
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