1/2 x 20 thread takes up apx .050 per revolution. 1/4 turn takes apx .012. By adding a quarter turn, .012 is taken out of the total travel of the injection stroke, IIRC the lift is .232, so, if you only allow .220 of lift in a spot that has .232 built into it, it takes a bit of time, but something will go away, the weakest link, the crimp, push tube, cup, cam follower pin/lobe/roller, something. What happened in cylinder is not the result of the injector setting, it was either just time for it to happen, I think you said the engine had unknown mileage, or an issue with an overhead set. A cross head WAY out of adjustment can do this, 1 valve will open sooner/farther than the other and contact the piston, you see the reliefs in the piston crown? There is not much room there when the valves are open and the piston is coming to TDC, injection happens when the piston is at .266 from TDC, some say it's positive end of injection, others start of injection, that's another story. In a nutshell, the valves open and close in the last .250 or so of the stroke, so, if there is an issue with the overhead, at 1500 RPM, the valves on one cylinder will open/close apx 12 times per second, so there is a possibility, if things aren't correct, for any valve in any cylinder to make contact, weather it is by .0001 or more, with a piston, 12 times per second until something clearances itself.
This is one of the reasons I did not cover cross head adjustment in the overhead set post, it is very easy to get things wrong and cause issues.
What happened to your engine is/was a fairly common thing, can't tell you how many engines I fixed or replaced under warranty from that failure, you got lucky, worse case could have been an engine that about cut itself in two. Hard, next to impossible, to tell what went first, an intake or exhaust from the damage. If you repair the engine, be diligent on your inspection, I am going to assume that pieces went throughout the engine. ANY cylinder that has any debris in it should be replaced as well as the rods. If the crown of the piston is damaged and pushed into the liner, it is junk, the liners are cast and don't like pressures other than that from the combustion process. I do not recall if you are running the aftercooler as well as the CAC, but if you are, the core should be replaced, you will never be able to get all the little pieces parts out of the core fins. If you just have the CAC, remove it and take it to someone to have it cleaned, the pieces most likely migrated back into the cooler, they are there even if you think you don't see them. Rods need to be Big Cam rods, they use the 12 point bolts rather than nuts/washers. The oil delivery to the upper bushing is timed different, they are drilled off center. Small cam rods fit and will work for a time, but your engine has more than standard fueling and cylinder pressures, a rod from a SC will, in time have the upper rod bushing start to score, then attach itself to the wrist pin and then bad things happen, you will need to start looking for another engine. Heads are the same from NHC to NTC, you just need to make sure the little hole on the head casting under the rocker box is plugged or you will have massive amounts of blow-by, it will be because the manifold pressure enters the crankcase thru these holes, they go directly to the intake port. Tap them for 1/16 pipe and just plug them.
If you need anything, call me, more than happy to help out.
Oh yeah, you'll probably want to have the injectors looked at. All those little bits of metal swirling around in cylinder have a tendency to damage the holes in the cup, they like to get ovaled or pinched shut. Would suck to put things together and then take it back apart.
