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Spark Plug thread broke and stuck

I was replacing spark plugs for first time, didn’t know I needed to use a special “torque wrench” for it. I ended up over tightening my spark plug to the point where the thread broke off the rest of the spark plug and got stuck in the engine. I can’t remove it because the part where the wrench would attach to the nut came off with the rest of the spark plug. How do I remove the thread of the spark plug? 2009 BMW 328i sedan

Tow it to a shop.

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You could drive it to a shop, but it will be missing on that cylinder. Unplug that cylinders injector first.
Don’t wait and drive this for a month before repairing. BTW…you will set a code from the misfire.

I would avoid a shop that specializes in BMWs or a dealer. their prices will be much higher than just an independent shop.

They may just knock the rest of the porcelain into the cylinder, use an extraction tool, and then vacuum the porcelain out. I’ve done that a few times when cars were brought in for this problem. $300 to $400!!!

But the shop may insist that they pull the head to extract it. This will be expensive, but either way it is going to cost you a chunk. $600to $800

Next time…snug is good enough. I actually use a 3/8ths ratchet and only grip the handle down far enough that my thumb never leaves the head of the ratchet.


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You don’t need a torque wrench. You should not tighten the plug as tight as you can possibly get it… and now you know WHY!

Let’s see, broke a spark plug OFF in an aluminum head? Very high possibility you’ve also stripped the threads in that cylinder requiring an insert as well as the extraction. Think of it as a down payment on your education as a DIY mechanic.


Uh boyee… I would have to agree with Mustangman… You definitely don’t need a torque wrench when you are replacing plugs. I’ve never actually used one but I also dont go Bananas trying to cinch them down. You have a steel spark plug and an Aluminum head…so the plug most always wins this competition and strips out the head. But if you say the plug broke…you may have gotten lucky and not stripped out the head.

I’m afraid to even tell you that you should back out the other over tightened plugs… That may cause even more plug/cyl head problems/damage, so I don’t know if you should touch the other plugs, but if you do not… I wouldn’t want to be around the next time plugs need to be changed…THAT will be a “Special Day” I can assure you.

Depending on where the plug broke… It may actually not be that hard to remove. If it snapped off at the spark plug base where the washer is located… then there is no real tension on the plug threads…you relieved that tension by snapping off the plug base. It may spin back out without too much issue as it is not under any load really.

You most likely need the help of a Pro at this point. If you tightened plugs this tight, I’m guessing you aren’t that familiar with how to remedy such a situation and could easily make a bad situation worse.

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Another way to learn how tight to tighten plugs is to borrow a good torque wrench, find the correct torque spec and see how it feels at that point. Remember the torque wrench will probably be longer than your ratchet, so hold the torque wrench at about the same place you would hold your ratchet. It will probably surprise you when you actually feel the correct amount of pressure is required. Now you will have a reference on how tight to tighten them in the future.

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That is also good advice… When you have been doing mechanical repairs long enough it is surprising how close to the actual torque number you can get just by feel. The correct Plug torque number will feel quite low to your hand/wrench (as if you thought you needed to tighten them much more) compared to the torque you surely took them to in this case. I am literally cringing thinking about the other over tightened plugs…when do you want to deal with that? Because someone is headed for a possible bad day in that regard…

Except a torque wrench won’t give you an accurate reading held like that.

I believe he mentioned hand placement to simulate when the OP was using his smaller ratchet handle. The torque wrench he also referred to is the Click type…that clicks when reaching the correct torque which doesn’t care where your hand is located… as opposed to the old deflection type of torque wrench, which not many if any pros use but still work just fine.

Why I just spoke for tcmichnorth still remains a mystery however…

When I was a kid the only socket set we had was with a breaker bar. I learned proper hand tensions by breaking a few head bolts off my go kart. Really a shop needs to handle this and check the other plugs. A machinist would know all about how to grab what is left and turn it out.

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Look at the bright side. At least this happened at the end of 2018, and not at the beginning of 2019, which would really be an unfortunate way to start a new year :wink: This sort of thing happens all the time, including to pro mechanics, so don’t overstress. But don’t continue to drive the car either. Find other transport until you can get it fixed. It’s possible that you could fix it yourself, but the common sense thing to do is to issue this job to someone who’s already done it many times. This isn’t a job for a beginner diy’er in other words. I’d be inclined to use a well-recommended auto machine shop for this, they’ll have all the tools and seen it all before. Ask your shop who’d the best machine shop in town. Most good auto repair shops should be able to do it too.

Don’t let this dissuade you from continuing to be a diyer, but remember you don’t have to re-invent the wheel either. Get yourself a repair manual for your car. It will contain a page with all the important torque values for the engine fasteners, spark plugs, and sensors. If you go at a time the dealership shop isn’t busy they might be willing to print that page out for you from their electronic version of the shop manual. The BMW dealership in my area at least is very customer friendly about stuff like that.

Yeah could have been a worse way to end 2018. They reported a car fire on I35. Poor guy. No dealerships open tomorrow.