Hey gang, I'm confused..I thought I blew a head gasket on my 250 L6...When I got off the head this is what I saw. What did this? Jason
Subscribed cause I'm curious too. Almost looks like it got weak around the casting circle there in the center.
Looks like pre ignition with that spatter. Did you have a lot of engine ping/detonation prior to this. Detonation can get components hot enough to pre ignite the fuel if its severe. Now you have to figure out what caused the pre ignition. Lots of info on Google im sure.
Times two on Darrens diagnoses. Detonation did it. That pinging sound you hear when accellerating ? That's multiple tiny explosions set off spontaneously and colliding with each other in the cylinder. Poor fuel, not enough octane for the timing or compression ratio will do this. Seen it also break the rings and ring lands too.
that was cylinder #5..and cylinder #4 the electrode of the sparkplug was gone...it looked like it was burnt....could a large vacuum leak done this? Jason
If your very lean and combustion temps increase you get detonation which is 2 flame fronts colliding and causes that ping noise. It creates even more heat and then starts pre ignition where the fuel air ignites before the spark plug ignites it. So your firing the fuel before the piston is at or near TDC. Pre igntion is very violent and it doesnt take long to blow the hole you have. What you describe happening to the plug electrodes is text book.
Overheating can cause this too. These pistons are thin in the center. I had a 250 blow a heater hose and before it was noticed, the piston tops collapsed on three pistons. It never even blew the head gasket!
The spark is ignited well before TDC by the ignition anyway, it's the multiple flame fronts colliding that does the damage.
http://www.streetrodstuff.com/Articles/Engine/Detonation/ Heres a good link. "An engine can live with detonation occurring for considerable periods of time, relatively speaking. There are no engines that will live for any period of time when pre-ignition occurs. When people see broken ring lands they mistakenly blame it on pre-ignition and overlook the hammering from detonation that caused the problem. A hole in the middle of the piston, particularly a melted hole in the middle of a piston, is due to the extreme heat and pressure of pre-ignition. Other signs of pre-ignition are melted spark plugs showing splattered, melted, fused looking porcelain. Many times a "pre-ignited plug" will melt away the ground electrode. What's left will look all spattered and fuzzy looking. The center electrode will be melted and gone and its porcelain will be spattered and melted. This is a typical sign of incipient pre-ignition."
so I have to pull the 250 and take it to a machine shop and put new pistons and rings in??...and the early timing set that I have for the 250 Jason
Thanks guys... I thought my car would be up and running by next weekend....that was before I saw the hole in the piston. Jason