UrS4boy

This post was made by Jeff Gerner on Audifans in response to my AAN sparkplug ejection thread:

"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. "

js0ne

I remember seeing somewhere how many degrees to turn plugs with crush washers and tapered seats after they have initially mated with the head. Tapered seats obviously required less of a turn.

maciu

typical situation is when we have to reuse old plugs and washers had been crushed earlier

AUDIDOIT

Ive fitted and tightened my plugs for 80thousand miles now and i agree with the feeling tight rather than torqueing tight,i always slighty oil the threads and touch wood,all has been fine,and that includes living in very hot climate in the south of france to living in freezing amsterdam.
ps,still went in the garage tonight to check they were tight though,all this talk has been making me nervous!!ha ha
Damien.

Turbo_Anarchy

Tighten them till they are tight and they won't come loose. If they come loose they were not tight enough in the beginning. I have had my shop for twenty years and we have never had a plug come out from being loose and we don't torque them. We have had cars come in with loose plugs, but its usually from customers installing there own plugs and not getting them tight enough.

audidrvr

I checked my plugs when inspecting the coilpacks and two were kinda loose and they were the only two with what I would consider excessive oil at the bottom. I would guess the oil was from a leaky valve cover gasket that was obviously recently replaced before I purchased the car. One was tight but certainly not to spec and only had a little oil residue and two were properly torqued with no oil residue. First I checked them then a day or two later I pulled them to do a compression test and thats how I know about the oil.