Ok. So a few weeks ago I started getting a P0300 and fouling the #7 plug. I found the main vacuum line broken. I fixed that but noticed blue smoke as I would rev the engine after I fixed it. I have true duals and #7 was showing multiple misfires. I also had an exhaust leak on the header on the other side. I started getting a P0300 . I used a boroscope and thought I had a chipped piston and so I pulled the motor and took it apart and this is what I found. Any ideas what caused it? It looks like it happened over time not really quickly.

The cylinder walls all look fine. No scratches or marks whatsoever on the cylinders. Just the valves on #7 have alot of carbon buildup on them on the #7. I pulled the #7 to check the rings and they look fine. Not cracked, broken or stuck. I decarboned the pistons and got them good and clean. Any thoughts or suggestions??? #1,3 and 5 on the heads look fine and 2,4,6,8 all look great too. The last picture is of all the pistons after cleaning.

 

Check your valve seals on that cylinder. Also u should have done a compression test before tear down. It would have let u know if rings were ok.

 

Looks as tho # 7 hg fire ring is leaking near the coolant passage.
Main vac line off created a lean condition??
Just because the rings look "fine", doesn't mean they are GTG. #7 is either pulling oil past them, or the valve seals/guides are leaky.
Cam flat on #7?
You pull a leak down B4 U took it apart?

 

I did a leak down test. 70% on #7. Compression was low on 7 too compared to the rest. With all the carbon buildup the valves may not be seating either which would also cause low compression right?
Caused a lean condition when the line broke and could have been cracked for a while before breaking. It broke at the rubber connection behind the motor.

 

I'm going to go ahead and put new rings on all of them since I have the motor out and they're all accessible. I'm also going to have new valve seals installed on both heads since I have them off. Motor has 120k miles on it. I might take those two valves out today just to see if anything is stopping them from seating properly. All my push rods are straight as an arrow and the lifters had no marks or scoring on them at all.

That's what has me baffled. I guess I could have washed the rings on that cylinder when it fouled the #7 plug and it quit firing. I just don't want it to happen again when I put it back together and back in the car.

 

I'd suggest touching up the valves while U have the heads off.

 

Yeah I plan on doing that too. I'm just baffled at what caused the problem in the first place.

I would have much rather pulled the motor and head and saw the "problem" not just the outcome of the problem.

 

I found the "problem". Completely disassembled the motor. The bottom of the #7 piston broke. Part of the ring went through the motor. Took everything to the machine shop yesterday. Block is fine. Just needs a hone. Crank is fine and no marks on the cam or lifters. So looks like a rebuild is coming.

 

that sucks, but it could have been way worse!

 

I've bean watching this thread, I knew this was coming. Bean down this road myself with number 7 cylinder.

 

Glad you found the problem, a lot of people keep driving with a misfire problem.. You didn't and saved %90 of the motor..

 

Glad you found the problem. I've been following this to see if I could figure out what it was. Glad you found!

 

Yeah I got lucky I quit driving it. To be honest, it ran and idled fine too even with the broken piston. It definitely saved me a lot of money stopping to find the problem instead of just continuing to drive it.


Soooo.... while it's apart. I might as well.......

Already put the Superhawk hood on. Got rid of more weight. A/C and P/S delete too. Installed the 8 point roll cage. Cleaning up the engine bay. (Can't put a clean engine in a dirty engine bay)