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Discussion Starter #1
I replaced the passenger bank plugs last night. I'm not using a torque wrench and never have for plugs. I've done a number of I-6 engines without trouble. I found that two plugs didn't really want to seat firmly. It seems as if the torque force would linearly increase instead of the abrupt stop that I'm used to feeling. I didn't cross-thread anything. The old plugs were stamped NGK BMW and were either original or dealer-installed at Inspection II. I had a sinking feeling so I pulled one and it looked ok. The threads were hard to see but I'm afraid they may be "knackered" as some of our British members would say. I started the engine and all is fine, no leaks or rough idle. So I have three questions: Is this normal for the S62? If a thread is stripped, short of pulling the head is helicoil a solution? Anyone been there? Thanks. Off to the driver's side.
 

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If the torque force each time is increasing, that might mean it's ok? I am not sure about this but in my experience if a thread is destroyed then it'll never tighten up and often the remnants of it can be found on the bolt/plug after removal. If it's tightening it's as it crushes the washer to get the seal. Perhaps put a torque wrench on and see if the torque is suffficient. I imagine they could be helicoiled without the need for the head to come off anyway. Which plugs were they? Were they close to the front of the engine so easy to get to? But I am no expert, although I have recently done this to a rocker cover bolt lol

You can get spark plug helicoil kits. http://www.amazon.co.uk/dp/B00142GP...de=asn&creative=22206&creativeASIN=B00142GPNE

Will have to be very careful not to get too much crap in the cylinder when you do this, perhaps any excess could be sucked out?
 

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If it's helpful, I've had many different cars over the years where I've sworn I've stripped a plug during re-install, especially at the recommended torque values. For example, Audi recommends 21ft lbs on their I-5 20vt motors, and if you rely solely on that tool, the plug hasn't fully seated because the crush washer hasn't "crushed" and compressed all the way. Then the plug ends up backing out 10k mi later and causing all sorts of problems. I'd like to say what you're experiencing is that last full turn of the crush washer doing its job. I've since always done plug changes by feel and have never had a problem with a plug backing out or a plug being stuck in the head. But I'm also not taking any responsibility of you stripping out the remaining threads if in fact that's what's going on here. The torque force has never increased significantly during re-install for me, the seating of the crush washer lets me know I'm there. The plugs that came out the M5 were also marked "NGK BMW" so I knew they were original. New ones torqued by hand went back in tight. Good luck!
 

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Discussion Starter #4
So far so good. It may be the crush washer I'm experiencing. I saw no aluminum on the removed threads so hopefully there's no stripping present. It sure doesn't seat as firmly as my former cars. Hopefully I won't be firing 80 cal. missiles through the hood. LOL.
 

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Carbon assuming you got the 'right' plugs with the compressible washer you will feel resistance for about 2/3rds of a turn. This 'resistance without increase' feeling totally mimics the stripping thread sensation. Not surprised at all you hesitated. The problem for you now is that since your washers are partly compressed you can't use the 2/3rds rule anymore. I suggest a torque wrench for this procedure at all times, but you can scoot by w/ just the 2/3rds rule (printed on the Bosch box) on FRESH plugs only. Once that gasket is squished you get that rapid tightening feeling you were looking for.
I wrote about this in one of the original spark plug threads iirc.
$50 torque wrench from Sears. A small price for the safety factor.
 

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Discussion Starter #6
TM,
Thanks, that probably explains it. I looked more closely at the washer and while not maleable like copper it has a small rib which must be doing the compression. The thing is, is that the old plugs' washers still looked ribbed and not flattened. Go figure but I like your explanation. You would think a task as simple as this would go smoothly. With the remaining plugs I inserted and turned the socket by hand until I bottomed them out. Still, the tightening part wasn't as predictable as I was used to.
 

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TM,
Thanks, that probably explains it. I looked more closely at the washer and while not maleable like copper it has a small rib which must be doing the compression. The thing is, is that the old plugs' washers still looked ribbed and not flattened. Go figure but I like your explanation. You would think a task as simple as this would go smoothly. With the remaining plugs I inserted and turned the socket by hand until I bottomed them out. Still, the tightening part wasn't as predictable as I was used to.
Have your previous cars had taper seat plugs? Much more positive seating than the new plug soggy crush washer feel. I found the BMW torque spec clicked as soon as the washers were fully crushed.
 
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