The engine has +230K miles, I've put most of it but 20K mile. I do the service so I know pretty much what is going on (I think) with the car. But I'm a little bit lost as to what has caused the engine to fail.
It had the usual XJs knocking noise for quite some time. This year the noise became more noticeable so I payed a bit more attention to car (fuel consumption, oils and coolant level). The XJ started to loose power and, as usual in life, it came when I was really busy so no time to check. I kept driving it around until it quit, oil level was very low. I know I shouldn't have done that but did not have another car. The engine did not seize or overheat. I decided to remove the head cause I thought the rings were fried as pressure test values were very low. I found the pistons in really bad shape. The first time I remove the head, about +70k miles ago, was to swap it for another OEM head and pistons were in perfect condition.
Few things I noticed: Rocker arms were tight, Oil flowing through push rods normally although a bit low. I did notice the injectors connections were loose, plastic toasted.
I have made the decision to rebuild the engine (1st time for me) and I'd like your opinion on what could have cause the damage on the pistons with the limited information I'm posting.
Appreciate in advance your input.


Piston #1


Piston #2


Piston #3 and #4


Piston #5


Piston #6

 

That is what looks like severe detonation. If it was something running through the engine, the center of the pistons would have dents too. You will know for sure when you look at the bearings. If it was detonation, the rod bearing will be spotted too.

 

Thanks @5-Speed I'll look into detonation causes and problems as I have no idea what it is. Once I take the rods and bearings out, I'll post an update.

 

What grade of gas do you use? It also looks like some debris is lodged in the tops. Lot's of the other marks look too "well defined".

What's do the head and valves look like. Can you post a pic?

 

I've always used 87 gas. Shell or Exxon are preferred and seldom use from Walmart, Sams and alike.
The debris in the tops is like welded to it. In the beginning I thought I could remove it but that stuff is hard attached to it.
@Saudade I do not get what you mean with well defined mark. Do you main elaborate on it please?

 

Pistones 5&6


Pistons 3&4


Pistons 1&2

 

Is it possible your connecting rod bearings are shot or the rod caps have come loose and the piston is coming up past the block deck and hitting the head. Thats why the valves themselves and the piston dishes are undamaged because they are the high and low spots

 

It's like using a torch cut a bar of cold butter, it melts and leaves smooth edges and uneven surface, versus cutting it with a knife that leaves sharp edges and a "well defined" surface.

You can clearly see the edges of what looks like chunks of metal that got "hammered" into the block and head.

Can you tell if the fragments lodged in the pistons are steel? You can use a magnet since the piston won't attract the magnet.