Of the block?
Yep. The webbing is too thin on the block and it cracks. It's not too common but it happens and you can't do anything about it.
Of the block?
Well I'd say it's tuning.
Your pistons perty much prove it. They have some nice cracks on the top. The star pattern in the bowl is actually half in and half out of the bowl. That is advanced inj timing. Even if your bottom end didn't crack those pistons would of let go sooner then later. Those cracks coming from the bowl will just grow to the outside till they hit the ring land .
The cracks in the pistons and the crack in the block aren't related.The spray pattern should be in the bowl not up.on the lip like yours. That's from the piston still coming up the bore while the fuel is being sprayed early.
That one piston has 4 cracks that I can see and 1 of them is almost half way across to the edge. .
Pics don't lie, you asked why, this is why.
It did last a good while tho!
Assuming those 100% nozzles have been in for a significant amount miles, I'd have to say early injection timing should have fairly minimal effect on the block via "extra " strain. Unless, of course, that military surplus I'd always running late, lol.
100,000 miles.
You don't think pre-ignition puts extra strain on the crank?
The cracks in the pistons and the crack in the block aren't related.
It wasn't the tuning that caused the crack in the block.
Well I guess we will never know for sure , but I'm sticking to my opinion. Personally I think that engine has had a hard life with aggressive tuning that ultimately met it's own demise.
I'm not choosing sides here but adding timing can increase torque numbers, agreed? With emissions on Ag equipment and my experience with underground diesel equipment, power (fuel and air) can be down-sized for emissions compliance compared to a non compliant engine. If your already less than say 75 hp and you pull fuel out to meet emissions you can lose quite a bit of your torque as well, so remedy is to add timing. I can see it in off road engines, but something that you have free control of timing events and they're placed in an aggressive advanced setting.... I don't like the idea of that at all. I'm kind of surprised that one of these aftermarket tuners have not designed a strain-gauge type monitor system that threads into the glow plug holes to allow them to watch cylinder pressure changes with tuning.