Pictorial: How to Fix Stripped Glow Plug Threads

I'm not sure how that reamer is supposed to work, can't see a good enough picture of it.

The glow plug seat is a 60 degree included angle. I ordered a 6 flute 60 degree countersink with a reduced shank. I'll cut apart a glow plug to use as a guide and ream the center hole to accept the 1/4" shank, also need to turn down or grind the outside diameter of the countersink to something less than 3/8" so it fits the hole.
Also picked up some small round wire brushes to clean the carbon out.

Grigg

Of course you know that you don't want to take any metal off of that seat, right? The depth of the GP is dependant on that seat. BTW, when will your truck be finished?

I want to just skim the seat just enough to clean up and seal again, only a couple thousandths of an inch. Will this be a problem, how much room between the piston and the glow plug end?

It'll be a while before I finish the truck, busy with a house and shop at the moment. Also just sold the engine to a friend and I'll help him build an almost identical truck. I have a replacement engine picked out (same but newer; and nearly new) and will fetch it in about a month, then it'll be a little while before I get it cleaned up and swapped. After that I'll install the cab..

Grigg

That glow plug sits right over the combustion bowl of the piston so just giving that seat a kiss like that won't be a problem.

For future reference, my company distributes recoil brand kits and replacement inserts. I also have the correct ones (plus a whole lot more like oil pan inserts) in my personal stock in case someone in my area needs it done.

Sorry, been to busy to look at my own threads...

That countersink tool is way too expensive, but I guess it's the right one. But you can't take off hardly any material. I'd guess not more than 1/8".

Any time the seat is badly damaged, the head is junk.

Excellent write up, thanks!

I've received a few questions on how I fixed my glow plug problem, so here's a recap and update with some more pictures.

In short I removed the broken glow plug , cleaned out the carbon, chased the threads, installed a helicoil, and trued the seat.
Got the car back together and haven't thought twice about it.. at least 6,000 miles now.

Here's some more details on the problem and the solution.

The glow plug was twisted off.. The head had been removed from the engine/car and the mechanic was afraid to try anything, so I picked up the head and started by...

First yanked the hex part off the broken plug, then drilled out the softer core a little.
Tried a spiral type easy-out that typically works well, not this time though. It expanded the plug some, would have been better off not to try that.
Next welded some 1/4-20 nuts on (one at a time) and tried backing them off with a socket. That didn't work, but didn't hurt anything.
Finally just welded a piece of 3/8" rod to it, then with vice-grips it did come out just fine.
Usually the welded nut trick works, at least on other stuff, this time welding a rod to it worked...


With the glow plug out the threads were still there but pulled and misshaped some.

I cleaned all 4 glow plug holes and threads with appropriately sized bottle brushes and some brake cleaner.

Chased all 4 holes with a tap (M10-1), which I was able to get pretty quickly from my Snap-On guy.

The troublesome glow plug hole I continued to cut the threads most of the way down to the seat. This gives the recoil two stage tap a place to go without having to cut new threads with the first stage.

Then used Recoil kit 38105 which I found new on ebay cheaper than anywhere else. (Franko6 probably has them cheaper yet, but I diden't know at the time.) Tapped only deep enough for the insert.
Put some red loctite on the insert and installed it, then broke off the tang.
Test fit, removed and wiped the extra off a glow plug before the loctite setup.

The next step was to true the seat, which is probably what caused the problem to start with, carbon getting by a bad seat and locking the threads.
for this I used a 3/8" 60 degree countersink, same angle as the nose on the glow plug.
The OD of the countersink needs to be ground down some (I forget how much) so it fits in the hole. I did this with a 5C Colet spinner and a surface grinder.
Next you need a guide to center the countersink aka "seat reamer" to the threads. for this take a glow plug and trim both ends of it and ream the bore to match the shank on the countersink.
Also made a handle to be able to spin the "reamer".
This worked quite well, use the threaded guide to very gradually advance the reamer and just skim the seat enough to clean up all the way around, removing and checking frequently. I removed about 0.008" to clean up.

Here are some picture of the tools I bought, made, and used.


Grigg

There are some fine-tunes I have for doing the finish heli-coil.

Occasionally, I'll have the g.p. hang in the recoil threads. It could happen if there is dirt, a burr on the g.p. or on the threads in the head. If you aren't careful, you can drive the recoil threads ahead of the g.p to the point the heli-coil binds.

To avoid this, I put a 10mm deep socket over the g.p. and tap on the side of the socket lightly with a small hammer. That seats the heli-coil into threads of the head. The g.p. should be hand-tightened until it seats.

Looking back on the whole thing it sure was frustrating trying to figure it all out the first time and round up the tools, but very satisfying to be able to fix it.

If I ever run across another broken and stuck glow plug I would first weld something to the glow plug with the head still in the car, may save a lot of time and money if it works like it should.
What I did with the head off sure was easier done on the workbench, but more than likely could have been safely done on the car.

For the welding part I used a TIG welder and stainless filler with stainless nuts and eventually a stainless rod. Regular steel stuff should have worked, but still use stainless filler because the glow plug appears to be stainless.
Part of why this works, at least how I understand it, is the TIG welding can put a lot of heat into the stuck bolt or glow plug causing it to slightly expand faster than the surrounding material, crushing any rust or corrosion that has it stuck. It also gives you something to grab onto when there's nothing there. You can even build up a little pile of weld to get above the surface where you can get to it.

Grigg

As Grigg says, removing the plug that is stuck is a bit of satisfaction. One definite... they have to be finessed.

Some rules:

1. If you can't loosen it, tighten it. Don't ask me why, but particularly tight nuts/bolts/screws will very often move to tighten when you can't get them to loosen. Once moved in the 'wrong' direction, they will then loosen easier.

2. Work the bolt in and out, advancing out of the hole slowly. If you back out 1 turn and it tightens, reverse direction, advance it back into the hole and try again. That is a tapping technique. It will allow any buildup that is locking up the threads to have a chance to clear from the threads. I've taken 1/2 an hour to get a very tight g.p. from a hole. It beats a broken plug.

3. Use lubricants/ penetrants. Any solvent that will help smooth the process is a good thing. On particularly tough bolts, I'll let the engine go through several heating/cooling cylces to help the penetrants do their work.

4. Work on a warm engine. It doesn't have to be hot, but if the aluminum is warm, there is a greater expansion ratio compared to the steel g.p.'s. Any freedom of movement will help you get the extraction done.

5. Don't get in a hurry. I've never seen a job done better by rushing. Take your time. Be a good judge of breaking point. If you aren't sure, use a torque wrench to help judge your limits.

Good luck.

Well said, Frank!!!

-Rich

Good advice Frank.
One question: I know I've seen it somewhere, but can you remind me what the ~ maximum torque is that should be applied on the ALH plug when removing it?

Let me be Frank with you: (sorry)...

http://www.beru.com/download/produkte/TI04_e.pdf states that the 10mm plugs will break at 35 nM (25.795 Ft*Lbs)... To quote the document:

What should you do when the breakage torque has been reached?
On no account carry on turning - the glow plug could otherwise break. Instead, proceed according to the 3-point
programme: heat up - release -unscrew:
1. Heat up: Run the engine until it is warm or apply current to the intact glow plug through a separate cable
for 4-5 minutes - this heats up the glow plug and burns it free. [NB: not for the newer glow plugs !!!]
2. Release: Apply a generous quantity of anti-rust agent or multi-functional oil to the base of the thread and leave to work in for approx. 5 minutes.
3. Unscrew: Then start a new attempt to unscrew the plug and use suitable tools to release the glow plug from the cylinder head. (Do not exceed the maximum release torque – 8mm GP-20Nm, 10mm GP-35Nm, 12mm GP-45Nm. Make sure you stop before you reach the breakage torque, if necessary start a new attempt by applying heat.

Yuri

Thanks ymz! I always forget not to direct questions to one member because I really would like anyone's answers.

That .pdf is where I saw it...in fact, it has been sitting in my "TDI" file on my computer and I completely forgot about it.

Broken glow plug

I knew these could break but didn't know just how easily (the hex sheared off and turns quite easily while the threaded section stays firmly in place). Now I have this issue and a couple of related questions.

Can the car be driven with the sheared GP or will the cylinder lose compression and/or blow the center of the GP out?

Is there anybody in the southern New England area that can help me out with this problem without removing the head?

Thanks in advance for any and all replies.

Glow plug problems.

Sorry to hear that TDI-for-2. I have a similar problem. I bought my used 98 Beetle TDI a couple of years ago. When I went to change the glow plugs because cold starts in the winter were getting harder I found an unpleasant surprise. Not only were there two plugs that were near stripped, one plug was stripped and it looks like the previous "mechanic" glued the plug in place. I was able to loosen the plug but now it just spins in place. It's still in fairly tight but I can see bubbles coming out around it if I put some diesel fuel around it. Believe it or not, it still runs fine with the small leak. I was even getting 55 mpg with it. I've emailed Frank about a Recoil kit but I'm going to have fun removing that one plug. I'm just hoping I can get it out without it breaking. I'm betting you could run it without the glow plug until the weather starts getting down near freezing. I think you're going to see issues then. That doesn't give you a whole lot of time if you haven't taken care of it yet. Well, good luck.

i shudder to think, my threads will strip ...
_

TDI for two, in the same predicament, It was december when it happened to me in MD, went home to WI and it worked (albeit I had to cycle the plugs a few times) but it will run.

All,

I have been replacing glow plugs in my two TDIs (jetta 98 & Passat 97) since they were new. I have had a few be tight to get out. I am now in a pickle. I went to replace #3 on the Passat and it broke and spins in the head. I suspect that it broke just above the threads. The plug is very wobbly in the head.

Question: Can I run the engine to drive it to the shop?

I am a little concerned that the tip of the plug may touch the piston. BTW, the plug appears to have unthreaded about a 1/4" before it broke. I am considering pulling the head off myself but am concerned that I may be too much for me. I have pulled heads off before (not overhead cam) but worry about screwing up the cam timing.

Any thoughts?

JS, If you have to remove the head, the timing will have to be reset, but that is no big deal. check out the Articles section, A4 timing belt procedure.

If the plug moved off it's seat, you are in a pickle. Running the car with the g.p. off it's seat can create a burn path through the seat. If that happens, you can ruin the head.

You can get the g.p. out, but it's a matter of working the plug in and out using a torque wrench set at 30 ft lbs. The head of the g.p. snaps at 33ft lbs. The idea is to use a penetrating oil and thread cutting oil to get into the threads. When the plug stops turning and the torque wrench clicks, reverse direction and drive it back in. Keep working it and you'll slowly gain an advantage, thread by thread. When you do get it out, usually the threads need at very least, chased. If the threads are chewed up, expect to put a Recoil in the hole.

Update. I did get the rest of the GP out by grinding the center electrode down into the GP and using a left hand drill bit to extract it. I used a Dremel tool with a carbibe end cut bit. I did make a center electrode puller (in another thread) but it would not pull the electrode out. There were enough threads for a new GP to take hold but will need helicoil in the future.

Mary Bergel (Jetahh) came up with a novel way to plug the g.p. hole and keep chips from entering the cylinder. He suggested the foam ear plugs.

Roll them down tight and stuff them in the hole. They expand and fill the void.

Also, after removing as much debris you can by blowing air into the threaded hole, I use the engine to pop the plug out. Make sure the piston for the cylinder you are repairing is at bottom dead center. When you are done, turn the key to "START" and the plug will pop out.

In your thread you mention "hand tighten" the new glow plug. My Bently manual says to tighten to 11 Ft lbs. Do you suggest not torquing to the 11 lb spec?

deltatech said:

In your thread you mention "hand tighten" the new glow plug. My Bently manual says to tighten to 11 Ft lbs. Do you suggest not torquing to the 11 lb spec?

Click to expand...

Hand thread the plugs to get them in most of the way, torque to spec.

Hopefully I'm not in too big of a pickle with my current situation but any advice is greatly appreciated.

I pulled out two glow plugs to replace them on the 99.5 MKIV Jetta I just bought to clear the CEL. They both can out easily enough and I dropped the new ones in place and began spinning them. One spun in very easily, was torqued to spec, and looks beautiful. The other began giving me trouble from the start. It doesn't want spin in easily. I have only got it to spin down about 2 threads but at that point I am reluctant to go further because of the stress. Any ideas on what course of action I should take. I am reluctant to proceed because I don't want to strip the head. Thanks.

Use a back tap to clean out the threads. This goes in then expands and removes the carbon from the threads.

I also use a .40 caliber pistol brush to clean out the threads and the area up to the seat. I use the brush first, then wrap the brush with a cleaning patch to remove the grunge.

Do not squirt too much fuel (cleaning fluids) into the plug hole.

I do use a thin tube and air gun to go past the seat, into the piston area, then blow air in to blow out any loose trash in the plug hole.

I'm very new to this tapping work but I think I know someone who may have the right tools for the job. Question: Do I still stick an earplug or something down the glow plug before backthreading? If so what's the usual best way to get those out of that tiny hole? Thanks for the adivce DanG144.

Also would it be a 10mm back tap that I would need to buy? They are cheap on ebay but just wondering the exact size for those glow plug threads.

You need a 10 mm X1 mm back tap. I do not use anything in the hole for the backtap or the brush method. These should not be removing metal. As Frank says in post#1 when tapping for the helicoil, larger threads for the insert, where you are removing metal you need to block the hole.

Frank says it well in post #1 as far as methods.