Andy, I think you mean 'There is no reason to pull the BLOCK.' This is the reason to pull the cylinder head...
Bob and I had a little 'picture/ telephone' meeting.
Bob sent some pictures of the cylinder head. The statement by the mechanic was that there were no valves bent. But the #4 piston had an exhaust valve imprint into the piston. To be blunt, I don't think I've ever seen that imprint like that WITHOUT the valve being bent. I don't think the mechanic is correct on that point. There was also an imprint on #2 exhaust, so I would never put this head back onto the care without pulling the valves and checking the concentricity. The exhaust valves are bi-metal, friction-welded chrome-moly stem onto a inconel valve head. Any strike to the valve can cause the weld point between the dissimilar metals to fracture. Give that cylinder head around 500-2500 miles and the valve head falls off, destroying the cylinder head, piston, rod and sometimes the block. Don't do that. If the valve is bent the slightest, throw it away.
What is worse, the combustion chamber for all pistons, except for #2 have the leading edge of the combustion bowl melted off. That may be one reason the impact with the #8 valve left a relatively deep impression... the piston was soft to the point of melting.
This is an issue of melted pistons we often see from injectors that are either poorly set for flow volume or the age of the injectors has caused them to leak excessive fuel. Unlike a gasoline engine, where underfueling will overheat a cylinder, diesels to the opposite. Excess fueling will melt pistons. Therefore, controlling excess fueling for diesel injectors is a very important issue.
If you take a close look at the #2 piston, there is a radius on the top edge of the combustion bowl that is about a 3/16" radius. The worst melting is in the #3 piston, where the edge of the combustion on the exhaust side I would estimate to have a 3/8" radius, maybe 1/2". The loss of that metal not only weakens the piston, but there is a measurable loss in compression ratio.
In my opinion, the damaged pistons need to be replaced. But more important, the injectors either need to be replaced (They are supposed to be OEM) or repaired. With only 140k, there is something that has interfered with the nozzles longevity. We did not discuss that issue.
If they are original, as Bob thinks they are, I doubt there is much chance to repair. As Bob expects to retain a basically stock vehicle, the Bosch 706 or equivalent should be a perfect replacement, if they are set correctly for flow volume.
There is one other issue from the excessive fueling and heat issue. The cylinder bore, particularly the #3 cylinder, which was worst, have some vertical striping in the bore. The overheated piston was close to seizing. When replacing the pistons, the dimension of the bore should be noted and at very least, the cylinder bores need to be deglazed with a ball hone and re-ringed.
This is a lot of bad news for an engine with only 140k on it.
The last issue is a matter of the oil used. We are no fans of Mobile 1 in any form. Particularly, the 5-40 TDT, as we have seen ring and piston failures in hot climates. This engine's #2 and #3 pistons are showing the prerequisit markings of an engine that came close to seizing We recommened a change in oil brands.
