Blew a spark plug out - how driveable is it?

[Otter74]

I was looking through old forum posts a little bit ago looking for any historical reports on this and found one or two from years ago where the owner had to rethread the spark plug hole and did it with the engine intact. It doesn't seem so outlandish to me now that I read about it being done, and see photos. I have an outlandish hope that the threads are somehow OK but I am really doubtful. carreradpt, a comment of yours may have been on one of those old threads. The first time this happeend to be I did exactly that. Since my engine was completely rebuilt about 20k ago and the top end was done probably 17-18k ago there is no need for other work on the engine, just this. Maybe if I'd have left it with Charlie Hsu he'd have been able to do it with minimal invasion if his judgment allowed it, but I made my choice and it's my job now At least I'll be able to take care of some minor ToD leaks with the engine out.

[JTL]

I had the same thing happen in my 740 bimmer, while I had let a family member drive it for a couple of weeks. I didn't blame them for what happened but was pretty angry over the fact that they didn't tell me about it and kept driving the car. This thing sounded like a tractor at idle!
I did some research and decided to try to repair the plug threads. I rented a time-cert tool set from aircooled.net and bought some time-certs from amazon. The repair took me a couple of hours and was pretty straight forward. I put some vaseline on the tap to keep the shavings from falling into the engine, as much as possible. The plug torqued down nicely and has held fast now for 25k miles. My other option was to pull and replace the head; pretty major effort and $-wise.
I don't see any reason this wouldn't work on a flat-6. The access to the plugs is a little more difficult but I would give it a try.

Cheers, jt

[pampadori]

is there room to get your tap and insert tool down the spark plug hole without a partial drop to get below the frame rails?

[DNickel]

Originally Posted by SCadaddle

Holy Smoke! That dude in the video must have torqued that plug and insert to 200 ft. lbs. with a 1/2" ratchet setup!

That freaked me out as his arm started shaking! That and where are all the metal bits from the cutting tool? I guess it's an American car so just blow them by the valves?

[Otter74]

Originally Posted by JTL

I had the same thing happen in my 740 bimmer, while I had let a family member drive it for a couple of weeks. I didn't blame them for what happened but was pretty angry over the fact that they didn't tell me about it and kept driving the car. This thing sounded like a tractor at idle!
I did some research and decided to try to repair the plug threads. I rented a time-cert tool set from aircooled.net and bought some time-certs from amazon. The repair took me a couple of hours and was pretty straight forward. I put some vaseline on the tap to keep the shavings from falling into the engine, as much as possible. The plug torqued down nicely and has held fast now for 25k miles. My other option was to pull and replace the head; pretty major effort and $-wise.
I don't see any reason this wouldn't work on a flat-6. The access to the plugs is a little more difficult but I would give it a try.

Cheers, jt

Glad to hear it worked out on your 740. I've seen enough that I'm confident that it's OK to do on my car. And thanks for the aircooled.net mention - I didn't know about the tools you can rent from them.

Originally Posted by pampadori

is there room to get your tap and insert tool down the spark plug hole without a partial drop to get below the frame rails?

Not sure, as I'd have to see how much space whatever tool needs. Off the top of my head, without actually being at the car, I'd say I have about 6" clearance straight out from the surface of the valve cover with the engine in the car. My bigger concern, rather than merely space, is how hard it is too see in there. Even with my clutter-free engine compartment it's a lot harder to get access and to make sure you've got things lined up correctly compared to when you can look straight into the hole.

Speaking of which, this is the best photo I got this morning with my phone:





Hard to tell any deeper, but the first few sure look buggered.

[Flat6pac]

I still have a time believing all threads are wiped.must have used the Hulk to install
A loose plug is only going to wipe the threads that can no longer hold the plug under compression
Bruce

[Walt Fricke]

Otter:
The picture, as posted, is backward. If you flip it horizontally, it will look like what your eye would see if you were a rubber pinhead and could get in there and look directly (or had it on an engine stand). #6 is right next to the top of the oil cooler, which you can see in the snap shot.

The cylinder head has two drillings through the fins. The lower one, which is a straight shot in, is where the head stud is, with its round 10mm stud barrel nut - the things you tried to retorque/test and some confusion arose.

The second drilling is right above it, and is for the spark plug. The spark plug is not a straight shot. It angles up and to the rear some - that's the angle you have to set your spark plug wrench when R&Ring a plug on the right bank (up and forward on the left bank). If you pull the #1 plug and look in there (where you can stick your head), you will see the layout.

So my guess is that you have a fine photo of a head stud barrel nut.

[911obgyn]

Just spitballin here, if you did a partial engine drop and pulled the oil cooler can you get at the plughole? On a turn of the century vw beetle i screwed up a valve trying to install a helicoil type spark plug insert, hit the valve with the tap because i neglected to put that cyl at TDC. use grease on the tap to keep the shavings from dropping into the cylinder.

[nomore]

It can be hard enough just to get the plug threaded back there normally w/o crazy gyrations and extensions and swivels, I can't imagine helicoiling the plug threads. That is crazy talk. Sounds like the car is safely home. Take your time and do it right.

[otto_kretschmer]

Originally Posted by Otter74

but I'm not willing to bet on the odds that cutting lube will hold all of the shavings from cutting new threads and keep them out of the cylinder.

the idea is to grease the tap and slowly cut the threads a little and pull the tap out and clean it and repeat until all the new threads are cut and then install the insert

but if you got home I'd just drop the motor and pull the head and install the insert

[SCadaddle]

Originally Posted by nomore

It can be hard enough just to get the plug threaded back there normally w/o crazy gyrations and extensions and swivels, I can't imagine helicoiling the plug threads. That is crazy talk. Sounds like the car is safely home. Take your time and do it right.

It's really easy and basically foolproof if you will use about an 8" straight section of rubber heater hose or vacuum line that will fit over the tip/cap and snuggly onto the ceramic insulator of your new spark plug. You can then thread them in by hand and pull the hose off once the plugs are initially seated. Use the socket-extension-ratchet only to take the old plugs out and snug up the new ones you install.

[Otter74]

Originally Posted by Walt Fricke

Otter:
The picture, as posted, is backward. If you flip it horizontally, it will look like what your eye would see if you were a rubber pinhead and could get in there and look directly (or had it on an engine stand). #6 is right next to the top of the oil cooler, which you can see in the snap shot.

The cylinder head has two drillings through the fins. The lower one, which is a straight shot in, is where the head stud is, with its round 10mm stud barrel nut - the things you tried to retorque/test and some confusion arose.

The second drilling is right above it, and is for the spark plug. The spark plug is not a straight shot. It angles up and to the rear some - that's the angle you have to set your spark plug wrench when R&Ring a plug on the right bank (up and forward on the left bank). If you pull the #1 plug and look in there (where you can stick your head), you will see the layout.

So my guess is that you have a fine photo of a head stud barrel nut.

Walt, I noticed that the photo got posted upside down but I couldn't tell the difference between the head stud hole and the plug hole without looking at it directly I know it by feel, though - i go straight down the hole in the VC and angle it towards the back of the motor slightly.

Originally Posted by SCadaddle

It's really easy and basically foolproof if you will use about an 8" straight section of rubber heater hose or vacuum line that will fit over the tip/cap and snuggly onto the ceramic insulator of your new spark plug. You can then thread them in by hand and pull the hose off once the plugs are initially seated. Use the socket-extension-ratchet only to take the old plugs out and snug up the new ones you install.

I wish I had thought of that when I was working on it last week. I knew that once, but had totally forgotten it. The people in the SJ Wagoneer that stopped to offer help and follow me back to dinner suggested that (and produced some hose) and indeed it makes it easy-peasy.

Given the above re: grease and doing it safely in the car, and that taking the head off is going to be, I dunno, triple the work, I'm probably just going to drop the motor onto a furniture pallet and do it there.

How do I do a partial drop? That is, what do I remove and what do I not touch?

[stownsen914]

Not sure if it was mentioned here, but isn’t there a tool or kit that includes a contraption that extends into the head to capture shavings from the tap / thread chaser? I think I’ve seen threads on Pelican about it. That’s what I’d want to use for a job like this.

[Superman]

I drove a five-cylinder 911 for a bit. It's a little like driving a diesel Yugo.

[flskala]

The re-tapping of the thread can be accomplished. You will definitely need mirrors and a light with the periscope + the exact length extensions. Ironically I had a local buddy break the spark plug in his 3.2 as he was removing it. The electrode + threads were still in the head. An extractor plus the light plus the mirrors plus magnets got it out.

PM me if you need to.

[dannobee]

Walt is right, the picture is of the cylinder head barrel nut. But never fear, the repair is going to be the same.

Dropping the engine is pretty straightforward and, with proper tools, can be done in less than an hour. That will give you the best access and at least you could see what you're tackling.

Whether you pull the engine or leave it in, you'll need a deep thread repair kit like this. (The earlier version of this one is the one that I've personally used in the shop)

https://www.amazon.com/Lisle-65200-14mm-Plug-Repair/dp/B00RGNJ78A

Or this one. (Looks like you'll need to source the taps and inserts somewhere else though. More $$$)

https://www.stomskiracing.com/products/911-spark-plug-hole-repair-kit

Be careful, go slow, use grease on the tap, and it's a doable job without teardown. I've done the repair a few times with the engine in the car, and it's tight, but can be done. You might not have the luxury of years of experience though. The cause was that the spark plug was not tightened properly when installed. Over the miles, it loosened up and allowed combustion pressure to escape passed the threads. At some point the flame front acted as a torch and melted the threads on the plug, allowing it to blow out of the hole.

Do NOT attempt to do this without the piston down in the cylinder. If you have access to an air compressor, you can attach a piece of steel tubing to the end of a blow gun and stuff that down the hole to blow out any remaining chips.

[Otter74]

Dannobee, thanks for those product links. Dropping the engine does seem straightforward - I've done engine swaps on other cars - though if one says it can be done in under an hour with all the tools, I budget for at least two. Still, that's not a lot. I appreciate those product links - I think I'd be willing to spend ~$300 on tools to avoid a drop, especially because I can fix my triangle of death oil leak with the engine in the car (thanks, Megasquirt). Thabsks for the reminder to put the piston at BDC.

[da Vinci Dan]

I tend to go the simpler, more predictable route when faced with these dilemmas. I have found myself committed to projects that stopped making sense long ago. Case in point, I was fixing a barn door a while back. Thought I could do while it was still hung. Like you I did not think I needed to take her down... Three hours later, I took her down and did it the easier, and BTW, more enjoyable way.

Have fun. Don’t struggle. You know what to do with the engine out.

Edit - and if you have not dropped a 911 engine yet... it’s time you lose your virginity!! You will know and appreciate your car so much more.

[911pcars]

DIY? If you're confident of your skill set, go for it. If not, don't make it worse. Sublet the repair to a good tech. Find one first and get an estimate. My WAG, $200 labor, but that's just a guesstimate.

There are techniques to gather aluminum drill shavings. However, al shavings can be vacuumed from the combustion chamber; ferrous materials with a magnet. Stainless steel Helicoil repair threads have a tang that is broken off to finish the installation. Make sure you account for that. In addition, position the piston at TDC with valves closed. A boroscope borrowed from your FLAPS will come in handy to inspect the chamber for other debris/damage.

S

[dannobee]

You do NOT want to put the piston at TDC. The tap will bore right into the top of the piston. Turn the crank until the piston drops down in the bore. Removing the chips from the cylinder is easier by using the small pipe down the hole and blowing them out than by vacuuming them out. Vacuum simply doesn't work. Like I said, I've done a few of these. BTDT. The tool that I referenced comes with inserts that stay in place by deforming the last thread with a special tip that's included in the kit, along with using red loctite. There are no tangs to lose into the cylinder like with helicoils.