UrS4 Frequently Asked Questions

“…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. ”

I questioned Scott on his reasoning and he replied:

” The thinking (and this procedure was given the ‘green light’ by my contact at Bosch) is that it’s quite possible that there is a variance to the crush washer ‘tension’ present for each hole condition, and the torque, then retorque procedure (immediately following – read no heat cycle) allows them all to more properly set to the conditions present in the given port of entry. The key IMO, is that the 22lb-ft torque spec is used.”

Vincent F then chimed in with:

“Dave, If I may jump in, the method in the madness of the double 22 lb-ft theory has to do with the material elastic and plastic behaviour.

The short version, if you already know the lastic-plastic-break curve of materials, is: The crush washer is a spring. At 22 lb-ft, you’re only halfway through the elastic zone, so it will spring back (elasticity) if you
back it out, the same as a suspension spring compressed halfway. A suspension spring will spring back with no permanent deformation but the crush washer is a poor spring design (compared to a coil that wouldn’t fit
there anyway) made in cheap material (compared to a suspension coil material). So even halfway through the elastic zone, there’s already some
permanent deformation (plasticity), which is a good thing in this case. By torquing once at 22lb-ft you deform all the crush washer to the same spec, thus removing some of the original variation from the manufacturing process. When you retorque, you have crush washers with have much less variation so your sparkplug are more evenly torqued than the first time. Now, heat
cycling (driving) a compressed spring may deform it depending on the material, and probably do with the cheap material used in crush washers, even when within its elastic zone. So it’s not advised to back out and
retorque a sparkplug after driving because you don’t know how much elasticity the crush washer have lost so you have no way to know how much it
should be torqued now.

You can check the “only halfway through the elastic zone” by comparing 22lb-ft torque to the torque by feel where you basically go through all the elastic zone (slowly increasing torque) then a bit through the plastic/deformation zone (rapidly increasing torque). 22lb-ft is well within the slowly increasing torque, i.e. elastic zone.

Now, when you torque by feel, you’re deforming the crush wahser, though not killing it really, it still has some spring left. So it’s not advised, in that case, to back out and retorque, because, as after heat-cycling, you
have no way to tell how much you’ve killed the crush washer and how much you should retorque it.”

Dave here again – I think I understand all that. I know that next time, I will follow the torque and retorque procedure suggested by Scott J. – on the new plugs. And then check for tightness, 22 lb ft, tighten only, periodically, after that.

HTH

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“Had it happen to me (#2 plug IIRC) several years ago. It also took out the
coil pack. This occurred at the time when I just had the MTM 1+ set-up.
The fix required a threadsert installed, fortunately with the head in place.
After going down the slippery slope with an RS-2 setup & MRC SW, I
religiously checked torque at every oil change (3000 miles) and insured that
I had 22 ft-lbs. A few times I did find a plug whose torque had dropped off
a bit into the 15-18 ft-lb range, but obviously the preventive checking is
sure better than the results of a plug being blown out. Mike B”

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“Well, as I would probably qualify as a “kid” ; ) I can assure those
other “kids” that it does indeed happen. they can look at my repair
bills, photos, and time-sert currently in the head of my S6 to confirm. Matt L.”

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” 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). Scott J.” (a well known Chicago area Audi tuner)

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“It doesn’t just happen to AAN plugs.

It happened to my old A4 1.8T- plug got very loose, then blew the electrode into little pieces that went throughout the intake manifold (don’t ask me how that happened), caused head damage to the tune of $2500.

I don’t have photos, but it’s well documented on the list, cost me two weeks in a rental car as well. Taka M”

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“I suppose I can dig out my hefty repair bill and scan it. It did happen to me at 135k. Now I check them with every oil change. It’s not like it’s a huge effort! Paul ?”

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“For what it’s worth, It also happens to the stock ford 4.6 sohc v8…first hand experience.- and needs a similar repair. Peter S”

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“Sorry don’t have any photos, but I can tell you that I own three different S4′s (93 and 2-94′s) and both of the 94′s have had to have plug threads replaced with an insert- one each onboth cars. Happened to previous owners, so I
don’t know details of how or why. Tim D”

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“Count my AAN as one that loosens plugs (for the record for the “kids”). I have discovered in 40K miles of ownership at least 6 times when I had to tighten one (or more) plugs. I do my checks about every 2000 miles or so. Larry L”

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“I have not blown one out (yet – four ring fingers seriously crossed), but have over the years found 2 plugs slightly loose.

Also had a friend some years ago blow 2 out of a Ford Probe GT Turbo, and my daughters Mazda Protege blew one out 2 years ago.

It happens!!! Dennis G.”

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“Not just the turbo cars- I had my old 1984 CGT( mit 358k miles on it) toss the #4 plug on the way to work. It was the death kneel for the car but it happens- especially IF the plug threads are NOT clean when installed and the torque wrench readings are wrong. Paul C”

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That’s just the people who responded. There are likely more out there. Like the two local to me.

Hope this helps.

The other issue is the fact that these plugs can and will work their way out of the alumimum head with repeated heat cycles over time, if they are not tightened properly to begin with or are not checked periodically, e.g. every oil change. If they do blow out, they destroy the threads in the head and probably the coil. Not pretty.

When the plugs are checked for torque, they should just be tightened to 22 lb ft (30 Nm)and not backed off and retightened. Some people think that this is a “myth” that I created. They are wrong. The posts under this one relate to testimonials by people who have had a sparkplug blow out of their AAN head, reasons why this happens, a “new” torquing technique for new plugs and alternative spark plugs for high horsepower applications.

As usual for the FAQ, please make any comments in the threads, not the links below. (Thanks).