4.7 stoker melted piston help

[dirt5track]

I have a 4.7 that has melted down a piston for the second time (cylinder 5). After the first time I changed the injector, intake, and had the head checked out. The original injector checked out ok and I run at 12.5-13.5 on the wideband o2. The piston looks like it ran lean and I have not been able to find any vacuum leaks. Has anyone else run into this or have any advice for me. I am at the point of pulling this thing out and doing a v8 swap.

[JeepsAndGuns]

Just grasping a straws, but have you checked the cam/valves? It's not making any ticking noise is it? Could one or both of the lobes on the cam for that cylinder be going flat and just barely opening?

[krom]

can you attach a picture of the piston?

[eezee]

I had it happen on cyl #5 too. My problem was too high compression. It was ok around town but when I took it up to 60-70 on the freeway, it sounded terrible, piston 5 got hot and the pin started making a knocking noise. Had to build it again.

[dirt5track]

Photos of the Pistons

[krom]

what was the ring gap?

I haven't blown up a stroker jeep engine before, but that sure looks like the top ring butted to me. could be caused by improper clearences, or excessive heat.

What was your coolant temp.

What are you using to monitor air fuel ratio

[dirt5track]

I had a local race/machine shop build the motor so I can't say for the ring gap. The temps stay around 210 with the occasional spike to 225 while pulling one particular grade in my area when ambient temps are over 99 deg. I don't recal the brand but I'm running a wide band o2 and my fuel trim is in line. The 2nd piston I replaced the rings are within spec out of the box without any fitting needed. From my circle track days if the rings were too tight they would fail under the first up to temp heavy load. This motor lasted 5k miles of all around use in the hot summer temps. I can't imagine it would last that long if the clearances were off. I do appreciate your help, any other thoughts?