Spark Plug Thread Repair

**AndyP** · 14 March 2015, 17:52

Brain Tonks has done a Helicoil with the head on, the trick is to not let anything drop into the cylinder. A small pipe on the end of the Hoover will help.

Good luck

**Error404** · 14 March 2015, 17:54

Bummer dude

I think I'm right in saying the head needs to come off to heli-coil it as there will be some swarf and metal fragments generated and you don't want them in your bore. You shouldn't need to skim the head unless it is warped. You'll need a new gasket of course.

I'm going to check my plugs tomorrow....

**Wheeljack** · 14 March 2015, 18:09

I have done an in situ spark plug repair on an AAN, mainly to see if it would result in a reliable solution...40k miles (!) over the last 2 years with no issues whatsoever...

From my original Fri Jun 22, 2012 Post on MG:

I wanted to get a better look at things so I pulled the valve cover and all of the plugs. It was interesting that the gasket was fully hardened to brittle plastic in areas, especially around plug hole #4, where pieces of it were actually missing.

Broken coil…

It may have just spit these things out…

I can’t imagine they would have worked too well, given the picky nature of plugs in this engine.
I then modified my vacuum to allow me to get down in the spark plug hole to hopefully remove anything that may be in there.

Visually, nothing was apparent. Once this was done, I checked compression in all cylinders except #4, which was obviously not an option at the time. This was done on a cold engine (that had not been run in a year) with open throttle plate at .85atm.

1-155
2-160
3-150
4-TBD
5-160

To me, those seem like pretty good numbers for a low mileage AAN, especially considering the altitude.

So, then, I figured I would try to do the next repair for the next known problem-stripped spark plug hole in the aluminum head. I did quite a bit of research looking into what people have done to do these kinds of repairs and the results. Although most everyone recommends the head to be pulled to do this to avoid getting shrapnel into the cylinder, there were plenty examples of it successfully being done with the head in place and by taking the right precautions. And sometimes pushing the envelope needs to go both ways. There is a think called overkill, and it is what destroys budgets.

I like to know my boundaries and what you can and can’t get away with. I want to know how bad something can be and still work, just as much as I want to know how something good can make something work or work better.
Could I have just torn the motor down and rebuilt it for another 100K. Put a new head in with no insert. Sure, you could do that…I could then replace all of the other unknown items, too. In fact, I’ll need to think about t-belt service as I wasn’t able to get that answer from the previous owner. I may be on borrowed time.

Or, can you spend $30 and a couple hours of time to get the engine back up and running and have no issues. Sure, I may not want to go boost crazy with the insert, but the reality is that in many cases it can be a stronger setup than the original because the smaller threads are all steel and the aluminum threads get more shear area from the larger diameter of the newly cut threads. One thing at a time. The car was practically on the scrap heap a week ago.

When I initially thought of Helicoil, I was envisioning my previous experience with them, which was largely replacing stripped derailleur hangers of early 90’s mountain bikes as a teenage bicycle mechanic. They were coil springs with a tang that you could wind in and snap off. So I didn’t realize Helicoil also has other insert products, namely a spark plug repair kit with solid inserts. Other companies have similar products, too. But I could get this kit from O’Reilly for $30 and see if it really could be that easy to get this fixed.

Repair Kit…

There is a tap, an expansion tool, and inserts of 3 lengths. The longest ones are the correct size for the 20VT head. Tap the new threads with a wrench. This went surprisingly easy. I then vacuumed out the bore and used compressed air to flush any remaining chips out. I alternated a few times just to make sure I had everything I could out of there. I figured that an aluminum chip or two probably wouldn’t be catastrophic, but without seeing the plug that came out of there (and intact eletrodes) it was hard to say whether or not something else could be in there.

There will be chips…

Minimizing the damage…

After a vacuum and flush session…

A pretty clean head otherwise…

Then apply some RTV to the OD of the insert and thread it in place with a spark plug. Expand the top of the insert with the tool and wait for the RTV to cure. I left the valve cover off during the test, as there was no use putting things back together if it all still needed to come apart. So the next morning, I set up the compression tester in #4 and cross my fingers. I almost didn’t want to look at the gauge.

4-165

F yeah! …<quickly goes to reassemble everything for test firing> I put a new valve cover gasket and some used F5DPOR’s in. I used the coil pack cover assembly from the s6 parts car (with a new coat of paint, of course). Then came moment of truth #2…and the gas wasn’t THAT old, right? Couple cranks and she fires right up and settles into a nice idle…but there is some smoking out of the exhaust. But it hasn’t run for a year, so that may just go away. So I kind of just let the car idle for a while and keep an eye on the vitals…water temp…oil pressure…all look great…smoking mostly went away during this initial running. There nipple on the coolant tank was cracked and was weeping at operating pressure. I swapped in the spare tank from the S6 parts car. Man, that is coming in handy.

**UrS4boy** · 14 March 2015, 18:26

Excellent post Wheeljack. Lots of folks have repaired their AAN heads this way (and therefore it would work on the 3B, ABY and ADU).

I have been preaching (yes, preaching) for years on the Audiworld and quattroworld UrS forums to always make sure that your spark plugs are tight (22 lb-ft, 30 Nm, tighten only) or suffer the consequences (i.e. sparkplug gets blown out of the head). Some people listen, others figure that it won't happen to them (until it does). Then they are surprised for some reason.

Checking spark plug torque is the No. 1 item in my monthly reminder post (admittedly not reposted here since Jan. 1st this year (until today)):

The spark plug post:

quattroworld.com Forums: Spark plug tightening - important if you don't like surprises

http://forums.quattroworld.com/s4s6/msgs/3757.phtml

The Audi Enthusiast website. Forums for all Audis including A4, S4, A5, S5, A6, S6, allroad, A8, S8, TT, R8, Q5, Q7, 4000, 100, 200, v6, v8, vintage, local forums

The monthly reminder post:

http://www.s2forum.com/forum/showthread.php?t=63388

Although the in-situ Helicoil solution takes the sting out of the problem, it is much better to prevent the plug from being blown out of the head in the first place.

**quattro-nick** · 14 March 2015, 18:40

i have done this a few times on other cars
just put some grease on the tap when you tap into the cylinder head
the small chips will stick in the grease

**s2driveruk** · 14 March 2015, 20:05

bad luck mate, looks like it is possible in situ so should be up and running again soon. Will check mine now just on the off chance but they have never budged in the past when i have gone to nip them up.

**Rusty** · 14 March 2015, 22:26

I did the plugs up a month or two back when I did the coil conversion and checked them then. Plug 3 was on it's way so torquing it would have stripped the thread there and then. Need to use some common sense when a torque wrench is involved

There's a place locally who does in situ repairs and if that's too dear I'll buy a kit and do it myself.

New engine isn't far away, 2 months maybe, so it just has to last until then, when the head will be looking for a new home.

**LSG** · 14 March 2015, 22:57

Pm sent

**UrS4boy** · 14 March 2015, 23:11

Originally posted by Rusty

Need to use some common sense when a torque wrench is involved.

Agree. Somewhere in the past, some ham-fisted gorilla must have over-torqued the No. 3 plug and weakened the threads.

Hope that wasn't you.

**popdemonic** · 15 March 2015, 01:56

Andy,I have done a numerous times on this things.especially on AAN.My UrS6 was stripping all
the threads whilst under the boost.I couldn't access to pull out the spark plugs on the roadside
since i didn't have any tools.I need to pull of the injectors connector and limped it home.
Buying Sav a Thread kits from Helicoils.
You can tap it by yourself.There're pilot threads on the tapping tool so the job is easy.the trick is
putting some grease on the tapping tools.whilst tapping, you just turn it 3 turn clockwises and
1 counter clockwise to remove the chips from the tapping thread and do it over again until you
passed the half way of all thread.back off the tapping tools and removed the chips,put some new grease
and start tapping again.By doing this,i have zero chips failed off the top of pistons.

PS.don't forget to put some high temp thread locker whilst you're putting the "Insert" back in.

on 9000 Aero

**Rusty** · 15 March 2015, 09:15

Cheers Pop. Lots of similar kits available online, do if the local place are expensive, I'll do it myself

**anthonys2** · 15 March 2015, 09:29

Hi Andy don't worry to much mate I got my garage to put a helicoil on one of mine about 7 years ago still no problems I just to make sure there was no damage to the engine and thankfully there wasn't hope you resolve it ok

**Unsprung dic Tecniqe** · 15 March 2015, 10:22

Originally posted by UrS4boy

Agree. Somewhere in the past, some ham-fisted gorilla must have over-torqued the No. 3 plug and weakened the threads.

Hope that wasn't you.

**AndyP** · 15 March 2015, 12:43

If you're going to do it yourself, I'd invest in one of these:-

http://www.ebay.co.uk/itm/USB-Endosc...item541b33f9ca

Just for piece of mind you can have a good look at the top of the piston to check that nothing has dropped in there

I've got one, they're brilliant, this is a video I took of an S2 piston that had injested the plastic injector seat

https://www.youtube.com/watch?v=9TVYSr3t9_U

Spark Plug Thread Repair

Spark Plug Thread Repair

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