Unfortunate adventures in spark plug ballistics

Yesterday son Neil and I ran the Frost Heaves Rally (TSD rally) around central New Hampshire. It was a great day and a fun event, and on one leg we scored our first-ever perfect score of zero. But that's not what I'm here to talk about right now. No, like the title says I'm here to discuss unfortunate adventures in spark plug ballistics. About 3/4 of the way through the rally we were toodling along through a free zone at 50 MPH when we heard POW!!!! followed by RUMBLERUMBLERUMBLERUMBLE.... Uh oh. That didn't sound good at all. I was thinking front half shaft? Exhaust? Whatever it was it wasn't good. We pulled over I couldn't see anything under the car. Opened the hood and couldn't see anything under there either. Exhaust manifold looks OK, exhaust looks OK, wait a minute... Why is the #6 spark plug wire hanging down? And why is there no spark plug where the #6 spark plug used to be? OK, now at least I knew what happened. I've heard of that happening, but I've never seen it, and I still have no idea what caused the plug to come loose, but to tell the truth I haven't really checked it for a while.

Anyway, the spark plug was naturally nowhere to be seen, and without a spare plug our rally was looking bleak. We turned around to head back to a little country store to see if they knew where we could find some spark plugs. About a tenth of a mile up the road, Neil says "There it is!" And there it was, lying next to the yellow line. Will miracles never cease. Picked it up, it looked like hell, but I put it back in, and the car ran pretty bad, but well enough to finish the rally. By another miracle there was an auto parts store open at the end of the rally, they had spark plugs, I put a new one in, and the car is running fine again.

After getting home I did some googling and discovered that this phenomenon is not unknown among M20 engines (and other BMW engines too). It seems quite a few others have experienced the same thing, and always with the #6 plug, just like mine. Has anyone else here ever had this happen? Suggestions? It seems that the typical solution is a helicoil insert into the head. Today I'll take a closer look at at it and see if I need to do something drastic like that. When I put the new plug in, it seemed to seat good and tight, and I drove 150 miles on it with no further drama, but now I don't know if I can ever trust it again, and I'm worried that it will be likely to happen again.

At least I know the compression is good.

__________
Dave
'91 325iX

Experienced something similar on my iX, but it wasn't the #6 plug (3 or 4). Had the hood open with the engine running and saw the plug moving back and forth a bit. It was my first car and scared the hell out of me. Since then I checked the plugs for tightness regularly, which was obviously needed. I never really trusted it.

I guess the #6 plug has it more often as it is less accessible.

Wow, strange!! Glad the hole wasn't stripped!!

alan

good story!

how does that work?!

Does it wiggle loose, holding on by the last few threads, and then the pressure blows it out?

I guess what confuses me is that it blows out past the threads, and you were able to thread a new one in and it stayed. It's good to know that works though. I keep a few spark plugs in my trunk, I'll be sure to at least give that a shot if I ever decide to play engine compartment pin ball

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 1 time(s). Last edit at 03/07/2010 12:17PM by Earendil.

The spark plug just unwinds over time, until no thread is left and it pops out. You won't notice until the last second (very few blow-by due to the loose plug + it is a 6 cylinder, you won't notice if one is running a little less well)

If the plug was not torqued correctly it can work its way out. Have had that happen on some farm equipment but not on my car. Usually the threads will survive but in an aluminum head there is more chance of damage to the head. What I do is put some anti-seize compound on the threads and torque them up close to the recommended. Never over torque plugs in aluminum heads.

Bob in Everett

I think you should change the title of this thread to "Fortunate" adventures. After all, you found the plug that came out and you were able to get the new one to tighten up in the hole. In an "unfortunate" adventure neither of these things would have happened.

John

Quote
John Yust
I think you should change the title of this thread to "Fortunate" adventures. After all, you found the plug that came out and you were able to get the new one to tighten up in the hole. In an "unfortunate" adventure neither of these things would have happened.

John

Absolutely. I agree Great story Dave.

The thing is;

Clean the wells before you start pulling plugs, the more time spent here the better off you'll be.

replace plugs cold, that's a dead cold motor

Always use anti seize on the threads, the carbon will work its way right up the threads and make pulling a plug ruin the threads. If you don't have any antisieze use grease.

Always use a fresh plug with a new gasket- no putting old plugs back in- never!

Tighten them just right, get to know what it feels like when the gasket is compressed.

Cheers, Rick

Thanks Dave, I had one blow on me on a race bike, just missed my leg!

Quote
Bob in Everett
If the plug was not torqued correctly it can work its way out.

This is what I sincerely hope happened! The alternative is that the plug was over-torqued and stripped the threads in the head, in which case it will happen again and I'd be looking at a helicoil repair. I'd rather just make sure that the plugs are torqued correctly.

It's funny that although I am generally a stickler for getting the torques just so on almost every bolt and screw in my cars, for whatever reason I've never used a torque wrench on spark plugs. I've always just gotten them "snug enough," which apparently was not good enough. From now on all my plugs are seeing a torque wrench!

Thanks for the help everyone!

__________
Dave
'91 325iX

Quote
Dave_G

Quote
Bob in Everett
If the plug was not torqued correctly it can work its way out.

This is what I sincerely hope happened! The alternative is that the plug was over-torqued and stripped the threads in the head, in which case it will happen again and I'd be looking at a helicoil repair. I'd rather just make sure that the plugs are torqued correctly.

It's funny that although I am generally a stickler for getting the torques just so on almost every bolt and screw in my cars, for whatever reason I've never used a torque wrench on spark plugs. I've always just gotten them "snug enough," which apparently was not good enough. From now on all my plugs are seeing a torque wrench!

Thanks for the help everyone!

Hi All,

Wow, what a thing. I suppose I should give my sparklers a test with the T-wrench. Given that they're supposedly correctly torqued now, what level should I set on the wrench? 15 to 22 ft lbs?

This is my first post from the JingleBerry (or FrazzleBerry or BlackBerry depending on my mood).

Cheers, Kelly

Quote
Kelly

Quote
Dave_G

Quote
Bob in Everett
If the plug was not torqued correctly it can work its way out.

This is what I sincerely hope happened! The alternative is that the plug was over-torqued and stripped the threads in the head, in which case it will happen again and I'd be looking at a helicoil repair. I'd rather just make sure that the plugs are torqued correctly.

It's funny that although I am generally a stickler for getting the torques just so on almost every bolt and screw in my cars, for whatever reason I've never used a torque wrench on spark plugs. I've always just gotten them "snug enough," which apparently was not good enough. From now on all my plugs are seeing a torque wrench!

Thanks for the help everyone!

Hi All,

Wow, what a thing. I suppose I should give my sparklers a test with the T-wrench. Given that they're supposedly correctly torqued now, what level should I set on the wrench? 15 to 22 ft lbs?

This is my first post from the JingleBerry (or FrazzleBerry or BlackBerry depending on my mood).

Cheers, Kelly

As long as it's not a dingle-berry I'd be careful Kelly; if you're in doubt about your plugs being tight throw a new set in. You did read my memo on that, yes?

I caution everybody on "torquing spark plugs", depending on thread condition this might be not a good thing; get to know what a crushed gasket feels like and use neversieze.

Rick

Quote
rkj

Quote
Kelly

Wow, what a thing. I suppose I should give my sparklers a test with the T-wrench. Given that they're supposedly correctly torqued now, what level should I set on the wrench? 15 to 22 ft lbs?

This is my first post from the JingleBerry (or FrazzleBerry or BlackBerry depending on my mood).

Cheers, Kelly

I caution everybody on "torquing spark plugs", depending on thread condition this might be not a good thing; get to know what a crushed gasket feels like and use neversieze.

Rick

Amen, brother. The only time I ever tried using a torque wrench to tighten a spark plug I stripped the threads right out of the hole. The afternoon tune-up turned into a much bigger hassle that day.

Kelly - once you get completely addicted those things are called Crackberrys.

John

Quote
John Yust

Quote
rkj
I caution everybody on "torquing spark plugs", depending on thread condition this might be not a good thing; get to know what a crushed gasket feels like and use neversieze.

Rick

Amen, brother. The only time I ever tried using a torque wrench to tighten a spark plug I stripped the threads right out of the hole. The afternoon tune-up turned into a much bigger hassle that day.

John

Thanks Rick and John. I guess I'll put down that torque wrench now. Like I said, I've never used one on spark plugs before, but it's nice to know I actually had a good reason for never doing it. I thought I knew what a crushed gasket feels like, but this episode had me wondering. Anyway, a new set of plugs is going in today, getting torqued by feel (and with copper-based anti-seize).

__________
Dave
'91 325iX

This happened on my 318i not long after I got it. The plug was still in the lead fortunately.

I rang the NRMA (AA equivalent) but they wouldn't come because I didn't know exactly where I was. I rang a mate who arrived with his new girlfriend (later his wife) that we knew nothing about. I was too worried about my new baby to notice his !

Only after he arrived did I realise I had a spark plug spanner in the standard toolkit in the bootlid.. oops..

I really never understood why they put a spark plug wrench in the tool kit. It is kinda a crappy tool but I guess if you launch a spark plug on the road, it is better than nothing. Perhaps the engineers knew something we didn't which is why they included it? Never had a car before or since that came from the factory with an "emergency" spark plug wrench!!!



alan

Most petrol cars I know had a spark plug wrench in the toolkit. I consider it standard equipment, especially on older cars (with carburettors), where you could flood the engine.

Well, I was replacing the front brake pads on my iS this weekend (seems like I wasn't the only one here working on my car over the weekend). Tried to do so last week but couldn't find my #7 allen key.

With all the work done and the girlfriend sitting next to the car enjoying some sun (and no airplanes), I went over the engine bay to check left and right. Just to have a look at them, I undid the spark plugs. I was surprised to find 3 of them hand tight and one just a little bit tighter. (and one had oil on the plug boot - leaky valve cover gasket probably and one had a rusty plug boot - huh?)

Put them back in, tightened them a bit, not too firm and ran the engine. Guess what: it immediatly sounded smoother at idle than before.

I have to admit that it's been a while since I last checked them (why did they put that cover over them, makes lazy people just forget about them, it's been 2 oil services since I last checked them), I'll keep an eye on it more frequently.

I tend to check on the plugs often, like every 5000Km or so, or whenever the engine hesitates or stalls when idle.
The engine burns oil, I take the greasy plugs, brush them and put back in, or replace if they look too bad.

I never had problems with the threads, much less a jumping plug!
Good luck!