Stripped #5 Spark Plug - Looking for perspective

[OldRanger]

Hi Folks,
Our 2002 170K mile M3 blew a spark plug out of #5 cylinder on a highway trip last Friday. The week prior, engine codes on #6 indicated a misfire and the car was running poorly, so my son replaced the coil and plug in that cylinder and it resolved the code. At that time, he also noticed the #5 coil was loose and discolored but there were no codes on that cylinder. I was helping remotely, but over the phone I didn't have enough information to assess anything beyond a worn out coil. So...we didn't take action at that time on #5. That information is mostly irrelevant...but I put it in there in case any of you have a similar experience of the indication that a spark plug is about to 'blow'. Maybe save yourself an uplanned breakdown.

Note: a reputable shop had recently (6 months ago) done a valve adjustment. So a professional was involved in the most recent spark plug removal/install. So, let's not dwell on why this happened and how awful it is. We ahve two high-mileage E46 M3s and this one is destined for track use. I'm just going to look forward on this one and bit the bullet.

Here's my 'ask' to the community: I don't have a spare cylinder head to take measurements, so I'm hoping for some help with that and also some informed opinions and recommendations. Does anyone know if there is sufficient space to tap the spark plug hole with Time-Sert tool 4212E and install insert 42125? Is that the right tool and insert? The tool is an M12x1.25 and the insert is M12x1.25x17.5mm spark plug P/n 42125. Although that insert is a bit longer than the plug threads, it's the insert that Time-Sert recommends for an M12x1.25 "3/4" depth spark plug.

Has anyone ever heard of this being successfully done on an S54?

Thanks,
Andy

[sapote]

Are you going to install the timesert raise above the original top surface or under cut the head and have the timesert shoulder flush to the head surface? If the timesert raises above the surface then the splark plug is not protruded into the chamber enough for proper combustion. Try to have the spark tip the same depth as stock.

timesert length 17.7mm is less than plug 3/4", not longer as you said unless I am missing something here.

The spark plug is the center and does not have much space from the valve seats, so after drilling the bad threads and tapping new threads, how much material remain from plug threads to the seats? Too little can lead to cracked head.

[OldRanger]

Hi sapote,

Thank you for your ideas and questions. Time-Sert tools in the kit include a seat cutter, and the instructions have a step for using that seat cutter to cut a seat for the insert flange. I believe this accounts for keeping things flush and properly sealing.

Calcuating the insert length per the timesert website: "TIME-SERT measures Thread Reach from under the washer to the LAST thread. EXAMPLE IF YOU GET YOUR SPARK PLUG LENGTH FROM SPARKPLUGS.COM
and your plug reach is 19mm subtract 2.5mm for the washer which is 16.5mm" When I looked up detail on the NGK spark plug DCPR8EKP - I saw the reach was 19mm (or 3/4"). I'm not good at math, nor do I have an NGK plug handy, but I think that puts the insert about a mm too long.

I agree that there is very little space, and I"m concerned about that.

One more thing: I am looking into costs to install a refinished head as a result of all of this, but I feel like this might be a temporary solution.

[OldRanger]

Food for thought. A reputable advisor thinks there is "some room for the Time-Sert".

(Again, I'm contingency planning. At the moment, the car is at a BMW dealership...I can only image what they will tell me. Towing destinations at 2:00am on a Saturday were limited)

[eacmen]

Hi sapote,

Thank you for your ideas and questions. Time-Sert tools in the kit include a seat cutter, and the instructions have a step for using that seat cutter to cut a seat for the insert flange. I believe this accounts for keeping things flush and properly sealing.

Calcuating the insert length per the timesert website: "TIME-SERT measures Thread Reach from under the washer to the LAST thread. EXAMPLE IF YOU GET YOUR SPARK PLUG LENGTH FROM SPARKPLUGS.COM
and your plug reach is 19mm subtract 2.5mm for the washer which is 16.5mm" When I looked up detail on the NGK spark plug DCPR8EKP - I saw the reach was 19mm (or 3/4"). I'm not good at math, nor do I have an NGK plug handy, but I think that puts the insert about a mm too long.

I agree that there is very little space, and I"m concerned about that.

One more thing: I am looking into costs to install a refinished head as a result of all of this, but I feel like this might be a temporary solution.

Personally I put pull a spark plug out and do accurate measurements on an actual plug versus specs from webpage.

Normal timeserts you cut into the surface for a flange that the insert sits in so that it ends up being flush with the surface.

I would think that as long as the plug seat is the same distance from the detonation chamber it should be fine. There should be more than enough threads to reach the torque spec needed.

[sapote]

your plug reach is 19mm subtract 2.5mm for the washer which is 16.5mm"

"TIME-SERT measures Thread Reach from under the washer to the LAST thread"
Why timesert length has anything to do with the washer? If the timsert flange is flush with the spark plug well bottom, then we just need the total length of the timesert, and if it is longer than 16.5mm then it is protruding inside the chamber, which is no harm depending on how far it is.

Btw, I saw a used good complete head on Ebay for $700

[Slideways]

M539 was able to fix three spark plug threads on an M70 V12 engine. His video shows the steps and tools he used:

[OldRanger]

I have the tools and insert(s). These appear compatible with the S54 engine (For others drifing in on the topic in general - they are not compatible with the M54 engine which uses a 14mm spark plug.)

Time-Sert Spark Plug tool 4212E (M12x1.25)
Time-Sert Spark Plug insert 42125 (M12x1.25x17.5mm)

Reputable mechanics have offered up their opinion that this repair is doable. A consensus is also in on the risk of aluminum shavings. Assuming there is nothing in the cylinder from other breaking parts, and assuming you do you best to capture most of the shavings in grease while tapping, there is no great risk with aluminum shavings in the cylinder. The metal that the head is made from is softer than the cylinder walls, piston, and piston rings. I have a camera (scope) to make sure there is nothing major in there and will modify a vacuum so I can get a hose in the cylinder.

If you're interested in what a dealership charges to fix this problem: I was quoted $1,900 for this Time-Sert repair from Century BMW in SC. This supports the conclusion that this repair is technically feasible when done by a professional (I am not).

They also quoted $8,300 for removing the cylinder head so a machine shop could do this on the bench. Really.

[heinzboehmer]

Nice. Timesert makes good stuff. I would probably trust that insert for a permanent repair (i.e. would not be looking to find another head).

[eacmen]

I have the tools and insert(s). These appear compatible with the S54 engine (For others drifing in on the topic in general - they are not compatible with the M54 engine which uses a 14mm spark plug.)

Time-Sert Spark Plug tool 4212E (M12x1.25)
Time-Sert Spark Plug insert 42125 (M12x1.25x17.5mm)

Reputable mechanics have offered up their opinion that this repair is doable. A consensus is also in on the risk of aluminum shavings. Assuming there is nothing in the cylinder from other breaking parts, and assuming you do you best to capture most of the shavings in grease while tapping, there is no great risk with aluminum shavings in the cylinder. The metal that the head is made from is softer than the cylinder walls, piston, and piston rings. I have a camera (scope) to make sure there is nothing major in there and will modify a vacuum so I can get a hose in the cylinder.

If you're interested in what a dealership charges to fix this problem: I was quoted $1,900 for this Time-Sert repair from Century BMW in SC. This supports the conclusion that this repair is technically feasible when done by a professional (I am not).

They also quoted $8,300 for removing the cylinder head so a machine shop could do this on the bench. Really.

You might want to make sure that cyl is in tdc so both valves are closed before tapping the threads.

Wild idea… Afterward might be worth taking a leakdown tester ”spark plug “ and modify it to pull vacuum.

But in all reality with the valves closed at tdc some well placed compressed air should remove any unwanted pieces.

[OldRanger]

You might want to make sure that cyl is in tdc so both valves are closed before tapping the threads..

This is one of the steps I'm trying to figure out.

I plan to replace all of the plugs and ignition coils, so I will take them all out first and be able to rotate the engine. I have a videoscope I am going to use. I was thinking I would rotate the engine so this cylinder (#5) is just before BDC in the combustion/power stroke and before the exhaust valves open. The stroke is 91mm (3.6 inches). That's plenty of space, since the tool only needs about an inch of space. There must be a happy medium to allow sufficient space for the tool and enough space so compressed air blows any junk out. I've never done this before, so I'm guessing.

[eacmen]

This is one of the steps I'm trying to figure out.

I plan to replace all of the plugs and ignition coils, so I will take them all out first and be able to rotate the engine. I have a videoscope I am going to use. I was thinking I would rotate the engine so this cylinder (#5) is just before BDC in the combustion/power stroke and before the exhaust valves open. The stroke is 91mm (3.6 inches). That's plenty of space, since the tool only needs about an inch of space. There must be a happy medium to allow sufficient space for the tool and enough space so compressed air blows any junk out. I've never done this before, so I'm guessing.

Get a leakdown test kit. You’ll know the valves are closes when it hold pressure.

Or if you have the valve cover off should be obvious when both valves are fully closed.

[OldRanger]

We did this repair today. Indications are that we’ve successfully solved the problem.

So:

1) these tools are the correct tools for an S54 engine
2) Timesert Tools are very well made
3) A videoscope is very useful - maybe mandatory
4) I’m not sure how to determine when the seat cutter step is finished…I think this is a judgement based on experience…which I don’t have. We guessed.
5) my vacuum tool I assembled wasn’t able to get all of the shavings out. Compressed air just spins the shavings around until they ball up together. Oh well, I got most of it out, and we started it nonetheless. No problems surfaced immediately. Thought: we did the tapping when the piston was approaching the bottom of the combustion stroke. So the next cycle is up and out the exhaust. I suppose remaining shavings just get blasted out.

Good fortune to anyone else that attempts this. I’m optimistic.

[sapote]

4) I’m not sure how to determine when the seat cutter step is finished…I think this is a judgement based on experience…which I don’t have. We guessed.

You want to cut the step the same depth as the timesert flange thickness, say 2mm, then measure distance H1 of head surface to top of plug well, then cut the seat until the distance = H1 + 2mm.

Thought: we did the tapping when the piston was approaching the bottom of the combustion stroke

I think drilling and tapping is best done with crank at 10deg after TDC exhaust for reasons: with IN vanos max retarded and EX max advanced the valves only opened 1mm or less and valves are away from the machining bits; With the piston near TDC it's easy to vacuum; then EX vanos to max retarded (crank unchanged) to open EX valves more than 6mm enough to blast out the remain debris with piston and debris at the level of the valve opening easy for them to blow out.
Most if not all debris were blasted out before piston and rings being moved and avoid logging any debris within the piston and cylinder wall.

[OldRanger]

I think drilling and tapping is best done with crank at 10deg after TDC exhaust for reasons: with IN vanos max retarded and EX max advanced the valves only opened 1mm or less and valves are away from the machining bits; With the piston near TDC it's easy to vacuum; then EX vanos to max retarded (crank unchanged) to open EX valves more than 6mm enough to blast out the remain debris with piston and debris at the level of the valve opening easy for them to blow out.
Most if not all debris were blasted out before piston and rings being moved and avoid logging any debris within the piston and cylinder wall.

I like this idea, and see the benefits in hindsight. Perhaps I was overly concerned about hitting the piston with tap, this was a primary concern for me. Also up for consideration: there is a complicating factor on blowing out debris if you use grease in the tap flutes. When I blew compressed air into the cylinder, it created a bit of a cyclone in there and the grease covered aluminum shavings just balled up together. Maybe use oil instead?

If anything surfaces that would indicate we have a problem from the shavings I'll follow up. I would expect the most likely issue would be damage to an exhaust valve if it closes on shavings stuck where it seats. I admit I don't have the knowledge to know if that's even possible. None of the mechanics I spoke with seemed overly concerned about this risk.

P.S.: I hear from a BMW Service Center manager of 20+ years that the BMW v10's blow plugs routinely.