Stripped #5 Spark Plug - Looking for perspective

[sapote]

About why the stripped threads, I guess someone had torqued the plug "to spec". I always am nervous when torqueing the plugs for this reason, and I just hand turned the plug until bottomed out, then torqued another 1/8 turns to crush the washer and done. For used plug, used less than 1/8 turns.

[OldRanger]

You didn't mention about drilling out the old threads before tapping; did you need to drill or just went straight to tapping? .

I did not do any drilling. The Time-Sert spark plug tool is designed to start in the existing (remaining) M12 threads in the cylinder head, which helps centering the cutting edges and keeping the tool aligned. Look back at the post with the tool pictured and the image should help. The standard metric tool kit (used in locations other than the spark plug hole) comes with a drill bit, the tools are shorter, and half the cost.

These tools are very expensive ($250). Funny thing about the whole job is that it's a $1.70 part (the insert) that is all you need. And a new spark plug and coil is advisable.

Similar but unrelated: different than the Time-Sert spark plug tool, when we found a lower shock bolt hole stripped on the trailing arm we used a Heli-Coil. That tool and process required drilling first, then rethreading and installing the heli-coil. And the tools was substantially cheaper.

[eacmen]

You didn't mention about drilling out the old threads before tapping; did you need to drill or just went straight to tapping? With drilling, it's hard to get the shaving with greased up drill bit due to drill speed. So it seems even with grease on the tap bit, there were greased up shavings dropped on the piston and it's hard to get them out with the sticky grease. I think it's hard to avoid the greased shavings dropping down. If this is the case, then maybe don't use grease at all then it's easier to vacuum the shavings out and blow the remain bits out of the EX valves. Did you turn the piston up near the valves before blowing the debris out? I would spend a fair amount of times trying to blow as much of debris out the opened EX valves and not hoping a running engine to do this task as there is a chance the shaving caught between the closing valves and the valve seats. You could do a leak down test on that cylinder to find out if it has leaking valves.

FWIW when I have done timesert I’ve put the drill bit in the hand tap and drilled the hole. Slow and steady greased drill bit when doing it by hand might work to catch shavings.

[sapote]

You didn't mention about drilling out the old threads before tapping; did you need to drill or just went straight to tapping? With drilling, it's hard to get the shaving with greased up drill bit due to drill speed. So it seems even with grease on the tap bit, there were greased up shavings dropped on the piston and it's hard to get them out with the sticky grease. I think it's hard to avoid the greased shavings dropping down. If this is the case, then maybe don't use grease at all then it's easier to vacuum the shavings out and blow the remain bits out of the EX valves. Did you turn the piston up near the valves before blowing the debris out? I would spend a fair amount of times trying to blow as much of debris out the opened EX valves and not hoping a running engine to do this task as there is a chance the shaving caught between the closing valves and the valve seats. You could do a leak down test on that cylinder to find out if it has leaking valves.

[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.

[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]

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.

[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]

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]

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.

[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).

[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.

[Slideways]

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

[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

[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.