Hello guys. Today I was driving on the highway, when I exited and came to the light my 95 accord was misfiring and running weird. Soon as I got on the gas it would run fine. I stopped at a store and left it running and all of a sudden I heard a loud pop. I drove it home 2 miles and it was very loud and no power. I thought I blew a head gasket. I just looked under the hood and the spark plug boot was off of it. I looked down in the hole and the spark plug is gone. It blew the spark plug right out of it. Is this a big problem, is it possible it unscrewed or are they know to blow it right out and ruin the threads. I can't tell if the threads are damaged because its too late for me to go buy new plugs. I've never seen a spark plug just blow out of the motor like this. Any help would be appreciated. 95 accord 4 CYL with a little over 300k miles.

 

Couple things are possible, & you'll have to figure it out. I've heard of it happening but I'm not real sure which of these things are more likely. A lot of times someone posts this kind of problem then never comes back to post the end of the story...

- Overtightened to begin with, so the threads are damaged. Some time later, the plug blows out, but the damage was done by overtightening earlier.

- Progressively unscrewing until it comes out. Possibly damages the first few threads, I don't know.

- Ceramic parts of the plug break, so "most" of the plug blows out, leaving the metal threaded part still in the head. Threads not necessarily damaged, but you have to get the remains out with a bolt extractor or something.

And...
WELCOME to HAF. I'm moving this over to General Tech where more people will see it.

 

Also... Thread inserts are available to repair the threads. I think more people here like the "Time-sert" kind instead of HeliCoils. I've used HeliCoil repairs a number of times & they work, but I haven't had to do that on a spark plug hole.

 

Ok thank you guys. I think I know what I have to do, and I will give a update. Sure was scary when I heard that thing pop. Thought for sure it was a head gasket.

 

Time-Sert rocks! Highly recommended.