Small dent or melt spot on piston

Replace all of the pistons. AFTER you hunt down the associated valves that are probably unable to set a seal when closed on itself. All valves have a precison ground angle around the lip of the working surface that must match itself when seating inside the head's home for it without anything getting between the valve and heads.

You also would probably consider that valve or two on the affected pistons (Probably all of them) are either late or early in opening. That means you pull Push rods, cam, rollers, lifters to see if any of them have gotten tired and is allowing the valve to travel outside of it's safe path when the engine is running.

A secondary concern is your timing chain. If that gets tired your valves will not be on time opening and closing or worse intruding too deep into a cylinder for the piston to punch it out and cause probably a destroyed engine before you know it.

Look over everything carefully.

 

I take my hat off in big respect for you.

I know a little something, but your post is full of good things for me to nibble on and consider the problem

LEarned something new today, thank you very much Sir.

 

Just my opinion but you already have it apart if you replacing a couple of the liners and one of the heads and whatever you might as well just do the in frame.

That's my opinion anyway.

 

How does that happen? Heat from preignition? Incorrect timing? Very over heated? Over fueling?
I would be concerned about the condition of the liner o-rings and vote for an inframe also.

 

i don't see melted, i see hitting, and maybe even some metal removed.

i'd be very suspicious of the valve springs being weaker as they aged. find out if there was ever any recall on them, or if there is a MB service bulletin on that issue.

there is a valve spring compression tool with a dial indicator, that one can test the valve tensile strength. but when rebuilding an engine, replacement is faster and cheaper than testing.

also the valve stems could also be of a weaker metal, maybe they were not hardened enough during the process of making them. again, check for MB service bulletins on that.

of course replacement new parts would be recommended.

and for the record, in all my years, i never heard of any MB engine in a class 7 or 8 truck going very long in miles, till they self destruct.

 

could be not only incorrect timing, bit also too much fuel being metered into the cylinder. i'd also check the fuel return line for a collapse, kinked, or blockage from maybe algae??

 

Good points there buddy but you need to put some more clothes on. My wife would block you out if she ever looked at my stuff. Mighty fine after working 48 years. Did you have a special parts washer fluid or something?