3.6L guys--anyone lose a spark plug while driving?
 

On the last session of a DE this weekend I hear loud "pop" and then loud exhaust sound coming from rear of car. I pull off the track and look under my car and a spark plug had come loose and won't tighten when trying to put back in its place. Apparently the threads are stripped on the inside and an insert can be put in place to accept the spark plug. How does this happen? Is this common?

Yes, I wouldn't say it's common per se but I have seen this before on other engines as well. Your mechanic can attempt to helicoil it to accept the new spark plug with the motor still in the car and hopefully can blow the metal shavings left by the process out the exhaust valve by turning the motor over by hand and blowing compressed air through the plug hole.

If the shavings get caught in there and don't blow out the exhaust, you may have to tear the motor down to the heads as you will hear what sounds like a rod knock when starting the motor...

My opinion as to the cause is that you had bad luck and the fact that these aluminum heads are soft material that have gone through countless heat cycles over the years. Nothing lasts forever unfortunately...

Good Luck. I hope it works out for you with a minimal of hassle and expense.

Ralph

last plug I saw blow out was on a Triumph Bonneville 40 yrs ago. Just a guess, but it was probably overtightened.

Quote: "but it was probably overtightened."
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The inverse can also be true. In American iron I have seen plugs blow out because they were forgotten/missed and not tightened enough. (time, vibration, pressure, backed them out). In those cases (and iron heads!) the threads were ok.

Always properly torque your plugs.

Overtightening is the most logical and also the most probable cause. However, I have seen a couple of heads where the spark plug was NOT overtightened. You can tell by looking at the crush washer on the plug...:)

Ralph

My son had one blow on his Ford Lightning pickup and a bit of research at the time proved that it was a relatively common occurance with those engines. Ford had a recall on it. But they are forced induction (supercharged) and you didn't say your 3.2 was. I assume it is normally aspirated, so typical cylinder pressures shouldn't (fingers crossed) be a problem...but they were!

I saw one back out of a 3.2, but there was no damage to the threads (on the plug or the head). Strange. Also, I have a helicoiled spark plug on my motor and it's fine. The only issue is that the helicoil usually comes out with the plug when I remove it. It's a bit of a pain, but I deal with it.

My car had Bosch Platinum +4's installed by the PO 40K miles ago. When I replaced them, 4 of them took something like 4 ft*lb to 'break loose'. The crush washers were crushed - so it seems like they can work loose if left in there long enough. Car ran fine though, and no evidence of blowby around the threads. I put in copper plugs and plan on new ones every valve adjustment, just to make sure.

I had the same thing happed on my 91 C2. I used the spark plug repair kit from Timesert. I was able to repair it in the car. I put lots of grease on the tap to catch shavings and "hosed" the cylinder out good before starting. It worked great.

john