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TDI 101 Got a simple/basic TDI question? Are you a newbie (new to the forums). Feel free to post your question here.

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Old January 29th, 2007, 18:33   #1
GRY_03TDI
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Unhappy Stripped glow plug, how to fix?

Well, my 03 had a bad #2 glow plug so I replaced them all, but the number 2 plug threaded just fine and then got real easy (stripped). I pulled it back out and the first two threads on the plug were smoothed over. Can you fix this by getting a new glow plug, tapping the hole in the head and banging things around in the garage out of anger. I am thinking that the tap would be a 12mm with 1.0mm pitch. Can anyone verify this? Also, anyone in the Baltimore area done this before so I don't end up screwing the head so bad it as to be pulled.

Great first post, huh?
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Old January 30th, 2007, 11:00   #2
BugBug
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I think the threads might actually be M11 X 1.0mm. In order to keep the shavings out of the cylinder, you will need to remove the head. Unless someone has a better idea to keep the shavings out of the cylinder. You might be ok if you chase the threads rather than drilling it out and inserting a heli-coil.
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Old January 30th, 2007, 14:01   #3
GRY_03TDI
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Quote:
Originally Posted by BugBug
I think the threads might actually be M11 X 1.0mm. In order to keep the shavings out of the cylinder, you will need to remove the head. Unless someone has a better idea to keep the shavings out of the cylinder. You might be ok if you chase the threads rather than drilling it out and inserting a heli-coil.

I was going to coat the tap in grease to catch the metal flakes. That is how most of the aftermarket supercharger kits have you tap the oil pan. Things may be different when working right above the cylinder though. Then change the oil after the initial startup. I was not planning on drilling and inserting a helicoil. Are you sure about the 11mm? I found the 12mm online and ordered that tap. Knowing my luck with all this it will be 11mm and I will have to order more stuff. Thanks for the reply!
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Old January 30th, 2007, 17:22   #4
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For a lasting fix... go with helicoil. Many autoparts stores will "rent out" a complete helicoil "kit" with all the fixin's and then charge you for what you used when you return it. That way - you do not have to purchase a tap... just pay for the helicoil you use.

Since there is about a 1/2 inch space between the threaded part of the head and the "sealing area" where the GP seats... I would think you may be able to plug that up with somthing below where you will be working with the tap. Then vacuum it out well.

Using grease may help... but be SURE, CERTAIN and CONFIDENT that you remove all the grease with degreaser (carberator spray, Isopropal alcohol..etc) - lest the helicoil may not stay in place.
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Old April 1st, 2007, 08:11   #5
knuckle-dragger
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Unhappy I'm there! Doing that!

90K, '03 TDI, and I just buggered the threads in a hole while trying to do a "routine" replacement of a bad GP. Deja Vu, no?

I was happy to see that others have done the same (I hate it when I invent a new failure!), but wondered what the end result was.

Before I start yanking the head, here the big question:

Did anybody heli-coil the hole with the head in place? If so, did it work????

I've replaced the timing belt, so I'm not afraid of pulling the head if that is required, but it is a heck of a lot of work!

Also: Getting the new insert perfectly aligned with the seating surface further down in the hole looks like a dicey proposition with a hand drill & tap. If the thread repair was done in place, was alignment of the hole a challenge?
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Old April 1st, 2007, 08:15   #6
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Somone mentioned inserting a foam ear plug in the hole to keep debis from gettinginto the head. That plus grease on the tap would be good.
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Old April 1st, 2007, 09:16   #7
ymz
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Yes, the foam earplug trick is very much needed here...

Some notes I've saved over the years:

The thread pitch is M10x1.00...

you could chase the threads with the correct size thread forming tap, NOT A THREAD CUTTING TAP. A thread forming tool creates threads by displacing metal, not by cutting.
http://www.precisiontwistdrill.com/t..._prod_taps.asp
http://www.mcmaster.com/

"The tricky part of chasing the hole with your tapping tool of choice
is to synchronize the tap with the thread that is already there. If the top threads in the head are too messed up this may be difficult to do. Just go slow and check your work after a full turn or so. If it looks like you are off synch it may pay to use a 10mm drill with a depth limiting length of tubing slipped over the drill, or device of some kind on it and remove some of the messed up part of the thread. CAUTION! Make sure that you have a definite way to limit the depth of cut! - When you take off a small amount of material the drill will tend to grab and draw the bit down into the good threads.

Then when the thread chasing is done rinse the hole with WD40 and feel confident to blow compressed air across the top of the glow plug hole to clear the debris, take a long handled foam ended swab on the threads, grab and unscrew the ear plug and it should help to clean the threads as well. When you get the top of the ear plug to the top of the hole blow it off again with air and remove. The bottom of the hole that I worked on was clean of chips and was dry.

Another thing is to clean the glowplug if it's going to be reused. I wound up taking a die to clean the glowplug of aluminum that had bonded itself to the threads on the way out."

(I forget who posted that...)

Good luck,

Yuri.


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Old April 1st, 2007, 18:57   #8
knuckle-dragger
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Thank you for the quick advice! I now have some thread repair tooling on its way to me, a rental car for the week, a foam earplug in the hole, and with any luck, I'll be back in operation in a few days.

I'll post an update on how things turned out.
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Old April 1st, 2007, 20:02   #9
kramnnim
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I've been planning to replace the gp's in my two TDI's, but reading this post scares me... Is there some way to make sure the threads don't get stripped?
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Old April 1st, 2007, 20:44   #10
ymz
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Quote:
Originally Posted by kramnnim
Is there some way to make sure the threads don't get stripped?
Well, there are very few guarantees in the world...

First, to try to make sure the GP doesn't break as you're removing it, you can clean the area (air) and use some penetrating liquid to remove any corrosion that may cause the GP to stick - especially if your car is getting on in years and the GP's haven't been out in a long time... Then, pay attention that the socket sits squarely on the GP and you put rotating force on axis and not at an angle... (clean up the liquid if you used any...)

When putting the GP back, put some copper-based anti-seize compound on the thread... (just a bit)... put the GP gently back in the hole, and slowly turn it backwards (counter-clockwise) a little bit 'till it finds the groove entrance... a little shake may be helpful in getting it square... then you can start screwing it in (Clockwise) by hand, only switching to the socket and handle when you've gotten it in a turn or so... you should pay close attention to the amount of resistance to the turning action...

Don't over-tighten... (it's only 11 ft*lb - just snug with your hand close to the socket end of the ratchet...)

Yuri.

PS: with all this, the glow plugs can still break off as you're removing them, and it's still possible to cross-thread...
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Old April 2nd, 2007, 20:31   #11
knuckle-dragger
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YMZ has it right: be gentle. My mistake was not logging on and looking around first! Had I known that 1) they are fine threads, 2) that the block is aluminum, and 3) that folks had troubles in the past, I wouldn't be where I am now. Here's what I did wrong:

I assumed that the GPs were robust little buggers similar to spark plugs. I just reached for the deep socket and started cranking. Two came out very easily, and two were difficult. They turned out fine, but there was a lot of friction the whole way out.

When replacing the plugs, I made no special attempt to put them in carefully and I didn't lube them up. The first two went in fine, despite my ignorance (they were the two easy ones on the way out). The third one didn't feel right going in, but it had been hard coming out. After going about 3/4 of the way in, the wrench torqued out. BUT... the torque went up very slowly and it didn't feel like it had seated correctly. It just kept getting tighter and tighter until the wrench clicked. Not a good sign. So I gently kept trying to tighten it. After about another 90 degrees I knew something was wrong so I backed it out. Sure enough! All the male threads were rounded over to about 3/4 of the way up. Then there was ~1.5 turns of thread that was filled with aluminum!

This GP wasn't "cross threaded". Rather, there was some corrosion or particle lodged in the threads that caused it to gradually tighten up as I kept deforming the threads. That's why I'm hoping a thread restoration tool (i.e. tap) will fix the problem without a HeliCoil.

Had I known what to look for, I would have stopped as soon as I encountered resistance. Heck! I woulda chased the old hole after it backed out with effort. I certainly NEVER would have tried to continue threading down a hole that "didn't feel right".

Clean it up before you back out the old one (throttle / carb cleaner soak followed by compressed air). Penetrating oil is a good idea too.

If you can't spin the new GP in using just your finger tips, something is wrong. Back out, take a break, collect your thoughts (and anti-sieze), and think it through. At this point running a chasing tap down the hole should work fine (use the earplug!).

There is no reason to strip the threads, and no reason to dread it if you know what could go wrong.

Oh yeah! That 4th plug? After messing up the third one, I took a day off and read this thread. Then I went back out to the car, cleaned up the hole (earplug, solvent, air, corkscrew to remove the plug), c-a-r-e-f-u-l-l-y hand threaded the replacement in, and all went well. The new one went in easier than the old one came out.

TCK

Last edited by knuckle-dragger; April 2nd, 2007 at 20:34.
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Old April 2nd, 2007, 21:09   #12
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LOL!

YMZ's copy and paste is spot on. I've replaced ans repaired a LOT and I mean a LOT of broken or stripped GP's.
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Old April 3rd, 2007, 13:27   #13
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Never remove threaded parts or fasteners from warm or hot aluminum! Work them out carefully only when the aluminum is room temprature.
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Old April 3rd, 2007, 21:02   #14
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And something I learned from DBW in a similar situation. Don't work on your engine if it is filthy. Take the time to wash it down so there isn't a bunch of crud sitting around the holes to fall into the cylinder or get stuck in the threads.
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Old April 4th, 2007, 05:46   #15
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That's a very good point! Get the greasy dirt, and sand out. Especially when pulling the valve cover. I use "Gunk" brand cleaner, but sparingly, and just on real greasy areas. Simple Green works on less greasy areas. I did find out a couple weeks ago that if "Gunk" gets in between the engine and transaxle, the clutch will slip for a couple of weeks.

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