Spark plug threads gone! Topic is solved

Wrenchinjoe · Post by **Wrenchinjoe** » 10 Mar 2011, 10:10

It has been a while since I last posted, but the trusty V70 has been rolling along pretty nicely of late... until yesterday.

1999 V70, non-turbo, 110,000 miles

My wife calls, tells me she is on the interstate and the car will barely accelerate, CEL just came on, what to do. She got off the interstate and after confirming the engine is not overheating that oil pressure is good she limped it home.

My code reader tells me P0304 - misfire in cylinder #4. I pull the coil pack and insulator and surprise surprise - they are both kind of melted. The spark plug is loose and the chute it sits in is looking sooty. After fishing the spark plug and some pieces of broken sparkplug & coilpack out of there, I confirm the threads in the head the spark plug threads into won't hold anymore - they are gone.

Question 1: What would cause the threads to let go like that. The plugs were last removed nearly 3 years ago after a timing belt replacement by a certified Volvo mechanic. If he had not tightened one or crossthreaded one, you would think it would have failed sooner.

Question 2: Can someone advise what thread repair kit to buy? Is it 18mm?

Thanks, I am really hoping that fixes it

mrjacobrussell · Post by **mrjacobrussell** » 10 Mar 2011, 11:06

please post pics of the plug before i can properly advise

Wrenchinjoe · Post by **Wrenchinjoe** » 10 Mar 2011, 13:22

I will try to take a picture tonight when I get home from work. Are you looking for a picture of the plug itself?

The old plug is a Bosch Platinum, and after poking around a little, I found the plugs are a 14mm thread. My local Autozone sells a repair kit for M14-1.25 spark plugs for approx. $30.

The old plug that came out looks pretty sooty, no clean shiny threads at all, so I think it has had some exhaust blowing past it for longer than the few minutes it took to get home. Yet, the engine ran smoothly, no hesitation, no missing... until it blew. So apparantly the engine can run normally even with a spark plug about to blow out of the head - go figure.

bobsnow100 · Post by **bobsnow100** » 10 Mar 2011, 13:34

Yes, just get a heli coil to repair it. The plug is 14mm . Shouldn't be too hard to do the way the engine sits with the plugs straight down.
Just google "heli coil" and you'll see many sites of how to drill and put one in. Shouldn't even take an hour

mrjacobrussell · Post by **mrjacobrussell** » 10 Mar 2011, 13:46

Possible piston valve damage please post pictures

Post by **JDS60R** » 10 Mar 2011, 16:10

Use a Time-sert for this application.

http://www.time-sert.com/

Wrenchinjoe · Post by **Wrenchinjoe** » 10 Mar 2011, 21:05

Here are a couple of pics, sorry that the one looking into the spark plug well is a bit blurry.

The plug is in better shape that I thought, it appears that the debris left behind in the spark plug well was mosly plastic from the melted/broken coil pack and insulator. The plug and the coil pack spring spring came out largely intact. I need to pull one of the other plugs to see if it has 2 electrodes on it, in which case one may have broken off this one.

Post by **JDS60R** » 10 Mar 2011, 21:36

Need a clearer pic of the piston top but it looks like you had some serious detonation going on. What do the fuel trims look like?

mrjacobrussell · Post by **mrjacobrussell** » 10 Mar 2011, 22:11

I'm worried about why you blew that out... But fords do it for no reason some times give the heli coil a try

Wrenchinjoe · Post by **Wrenchinjoe** » 11 Mar 2011, 08:39

What do the fuel trims look like?

Not sure how to check those.

I'm worried about why you blew that out...

Me too... the plugs have not been touched since a volvo mechanic changed the timing belt in April of 2008. We bought the car @ 9 years old with only 65,000 miles on it. We had the timing belt changed right away due to age rather than mileage.

I was planning to do the majority of the 105k maintenance interval myself once it warmed up a little (as I don't have a garage and have to work in the driveway... weather and children permitting) and spark plugs were part of that plan. Perhaps if I had changed the plugs 5k miles ago I would have cought the problem before it blew out. Woulda, coulda, shoulda I guess.