My son's 1983 244 GL has developed a peculiar habit since we did a tune-up ourselves. A couple of months ago, the #2 spark plug unscrewed itself, popped loose, and fell out of its sparkplug wire connector. We were able to find the plug, incredibly enough, put it back in and limp on 3 cylinders to a parts store to get a new plug. Recently, either the same, or a different, plug worked its way loose. What could cause this? Is it just that we didn't torque them down tight enough (we weren't using a torque wrench), out of fear we would overtighten and strip the threads? Or is this a sign of something severe, like a serious compression issue?
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83 240 GL

I was reading a book called Automotive Excellence, a book used to help certify mechanics for ASE, and I came across a section with torque values. Against what I usually read here, torque values include the use of antiseize, meaning that every bolt that you tighten to a specific torque should have some antiseize, or the like, applied to it. This overcomes the friction and makes sure the bolt is tight. You should apply antiseize to the threads and even the underside of the bolt head. Then you shoudl tighten to the specified value.

Smith

I agree that the correct procedure is to apply anti-seize compound to the threads of the spark plug. Get a balance-beam type 3/8" drive torque wrench from Sears for about $25, not the "click" type. (For $25, the "click" type are not reliable. I sheared off a front suspension bolt using one! The balance beam design is cheap but reliable.)

Never use a torque wrench as a pry bar. The torque wrench is your first tool for assuring a quality, reliable, result.

The bottom of the spark plug has a compression fitting. When you apply the correct torque, you are compressing it, forming a seal.

In addition, buy Bosch plugs and leave the metal, screw-on cap in place. The factory spark plug wires (BOUGICORD) require that cap to hold tightly.

Do it right, one time.

All the best,
Lama

Could be defective plugs that slipped through the QC station at the end of the production line. In your case, the defect would be in the threads (ie: OD undersized, cut too deep, etc.). What has the brand of plug? For cleaning the threads in the head, a wire brush used to clean 1/2" sweat copper fittings works well. jp

undersized hmm

Don't over-tighten the plugs in attempt to set the crush washers. The result could be worse - a stripped spark plug hole if you go too far.

Pull the plugs and clean the threads in the head with solvent, brake cleaner or carb cleaner applied with cotton swabb. I recently bought an '89 760 and had difficulty removing one plug. I don't think this plug was fully seated previously or it just worked loose. The entire thread was coated with 'varnish' from the exhaust gasses.

I cleaned the threads in the head as described above and was able to seat the plug properly. With the threads clean and a light touch of anti-sieze, I was able to thread the plugs into the head up to the crush washer using little more than my fingers on a 3/8" extension on the spark plug socket. This is also a good method to ensure that you don't cross-thread the spark plug hole.

Good luck,

Dan

You aren't tightening the spark plugs enough. They have to be seated firmly, or the constant compression pulses will back them out. I was guilty of not tightening angle seat plugs in Fords many decades ago, and two popped out just like you described. Figure about 15-20 foot pounds of torque and they will stay in OK. Be sure to use a bit of never-seeze on the threads too.

If you use anti-seize, then reduce the torque to 11-14 ft-lbs to account for the thread lubricant. Using a torque wrench is the way to go.

The plugs must still be tight - that's how they cool. They will overheat when loose. On the NGK plug, the washer must be crushed to take a set, and regardless of never-sieze, that still must happen.
I don't use a torque wrench for spark plugs - a good idea for those folks new to car repairs - but I have installed thousands of the things over the years, and not once have I stripped one. Usually I repair the damage caused by others.....

I agree: it's just important to know that when you use a torque wrench, the torque indication of a lubricated plug at the same degree of set is lower than that of a non-lubricated plug. I do it by feel, but for those who use a torque wrench they have to remember that fact.

With "abated breathing" I am awaiting a good explanation you might receive. Many times I've heard of this but never once seen it.

The forces necessary to do this even with an untightened plug seem overwhelming to my imagination, although the same forces do seem to move 3500 lbs of iron across large distances over steep grades.

When you install the plugs (I've never used a torque wrench for this) do you feel the seal washers crushing? Are the threads in the head known to be OK?
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Art Benstein near Baltimore

In response to this (and the message from scorch):

We did the tune up within the last, say, 3000 miles. So I only replaced the one plug that jumped out because the others (and the dist cap and the spark plug wires) were new.

I can't say I felt the lock rings crush at all; I was I suspect way too concerned about overtightening. I'll make sure my son is less concerned when he tightens them this week.

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83 240 GL

I think the most probably explanation is that the Swedish elves who live in the cylinders and whose job it is to push the cylinders down are unscrewing the spark plugs from within in order to get some fresh air. They are probably just a little old and tired. You should replace all four elves instead of just the one.

Those elves must hide from me.

Headlight Funkiness

Here's the Aye Roll post with the famous photography
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Art Benstein near Baltimore