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On the way back home from the in-laws on Christmas night, I had a Bosch Platnum plug (FR7DP) fail. The center electrode is gone and the insulator looks as if it has blown up. The plug has less than 15K miles on it. My guess right now is that the pieces missing from the plug got stuck trying to go out past the exhaust valve resulting in an improper seating and the valve burned, complete loss of compression in the cylinder. I have seen on some other boards where other people have had problems with the Bosch plugs losing the electrode, anybody here have any bad experiences with the Bosch plugs? When I showed my (independent Volvo) mechanic the failed plug, he looked at it and said it does not appear to be and he wouldn't think it was a detonation problem, and he also said that he would not recommend anything other than the Volvo plugs. The head is being pulled right now so hopefully once it is off there will be a better clue as to what actually happened.
He also wanted me to check with the board here to see if there are any out there that have had exhaust valves burn up. He has performed a few dozen valve jobs on 850's in the past two years or so, he said everytime there is a failure such as I have one of the valves has a little pie shaped cut out of it. I did find something in the FAQ here about 740's and 850's with hydraulic lifters where the valve guides are worn or defective. He said he has done this on motors with 55K miles up to 170K miles, mileage doesn't seem to matter. He has a good relationship with the local dealers and they have said that they have done a number of them while still under warranty too but could not give him specific numbers as to how many. Dealership/Volvo CYA if you ask me.
Guess that's it, besides my son crashing into a neighbors car and breaking the whole tailight assembly, this is my second suprise Christmas present. I don't want anything next year, thanks anyway. :)
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