I have a 2007 S4 4.2L M/T with 83,000 mi. Last week, while driving 55 mph, the Check Engine light came on and the engine seemed to be firing on 7 cylinders. I brought it into Audi service, and was told that the piston head hit the spark plug and broke the spark plug. The spark plug was replaced and the car appears fine. I'm told that a boroscope inspection revealed that the piston head was rough, and that it would break the newly installed spark plug, too. Their solution: replace the engine for $21,000. What could be causing this to happen? Is it possible that it would not occur again?

 

interesting..... first off you should post this up in the S4 section... but second your piston is not hitting the spark plug... unless possibly the wrong spark plug was installed in the motor... but after audi replaced it i would assume the correct plug is there... it could have been possible the plug was damaged by detonation and small parts of the plug could damage the piston, but really the piston will survive and the car will run fine with a new plug.... coils often go out in the 4.2.... do you know what the old spark plug looked like when it was pulled out? .... sounds like a load of crap from audi though about the piston hitting the plug... dissapointing...

 

If the piston were hitting the sparker the engine would barely stay in the bay, the ruckus from an unbalanced rod with at least 1/4 play would cause that thing to feel like your car is falling apart. My thought is that whoever installed the previous sparkers in there, maybe Audi, crosthreaded the block somehow, and that caused the plug to go in deeper than it should; or maybe incorrect gaping to begin with; or maybe fouled plug caused by a bad head gasket. Or maybe Timing belt, you're around the time to do a timing belt anyways...

 

^ S4 4.2's have a timing chain.

 

Thanks for the replies. Very good information. Audi of Greenwich, CT would now like to re-examine the car to re-assess their opinion of recommending spending $21,000 for a new engine.

Some other things don't make sense to me. When the piston is moving up the cylinder to compress the gas mixture, there must be a gap between the the top of the piston and the top of the cylinder. Does any one know the approximate depth of this gap?

Audi of Geenwich also stated that they used a boroscope to examine the inside of the cylinder, and they noticed that the sides of the cylinder were scratched as a result of the tip of the spark plug being broken off. Previously, I was told that the ceramic portion ofthe spark plug had cracked, but now I'm told that it is the small metal piece of the plug that forms the plug's gap. But how could that cause significant scratches to the cylinder walls unless this little metal piece were somehow wedged inbetween the piston and the cylinder wall . . . which is highly doubtfu?. The other thing that seems interesting is that this little metal piece was not found in the cylinder. So, it must have been ejected through the exhaust valves.

It will be interesting to hear what Audi has to say this week.

 

The only way for a piston to hit the spark plug is if the piston comes off the rod and even then the spark plug is in the cress of the head and thats not likely.

The B6 S4's have lots of cylinder wall scoring and issues. This link has more information
What does X look like. Cylinder bore Addition

 

Something doesn't sound right. Yes its a known issue that these motors suffer from some cylinder wall scoring in a few high mileage examples. But thats mainly due to how well the car was maintained in its lifetime. Could the fragments from the plug do some damage? Yes. But I find it odd that they're so quick to write off this motor just like that.

You say the car is running fine now. If its not burning excessive oil and compression test shows each cylinder is within normal specs, then don't fall for that pocket gouging. I'm guessing the only reason they're suggesting a new replacement is because, well its Audi of Greenwich, most of their customers are clueless about their cars and have deep pockets, and your car is not under warranty. If it was covered I highly doubt they'd want to foot the bill.

Have a leak down test done, monitor your the oil consumption and take it from there. Oh and replacing a new long block is roughly 15k. $13500 for a new motor and rest in labor. Ask me how I know.