Very common for even a good running engine to have main bearing web cracks. They crack at the bolt holes. Imo there are several contributing factor. Harmonic balancer is at the top of the list. Poor design and casting by GM. And lastly is getting them too hot.
The old 5.7 conversion engine used to crack around the head bolts, cracks around the mains, broken crankshafts, etc., but I have seen some with over 300,000 on them. I feel like at 318,000 my 6.5 must be one of the good ones, if it is the original engine. I have no idea about the history of the truck, other than every body panel on the truck is dented and scratched.
Oh no! Another 5.7 diesel knowledge guy- IS @WarWagon your friend? Haha
The mainwebs crack in my experience always from bad harmonic balancers. To be fair, non of these engines are well balanced internally. But I have not seen one that cracked with good balancers or that didn’t get some unfair abuse like hydrolock, or starting fluid blasting things apart.
I had timing gears on my hot rodded 6.5s back in the day.
DSG no longer makes them, so Leroy chased it down. http://leroydiesel.com/products/timekeeper-ds4-timing-gear-set/
The fords running same db2 injector pumps got much longer life from them than gm, and only 2 differences was 3/8” fuel
Line instead of GMs 5/16 and no chain to slap around the pump.
The only drawback besides price is there is slightly more drag on the straight cut gears than double roller chain. But worth it. Now if the drag is a concern, do what I am doing and send timing gears, and the ip gears to Chris for slip coating. https://m.facebook.com/TwistedSteelPerformance/
I don’t have (not sure anyone will ever bother to figure out) which is less drag between the coated gears vs chain. But it never hurts and will sure promote a long life, so Wether I gain or loose 2 hp now, it will be a bet gain not loosing 10 hp from timing chain stretch.
And less chain slap ever time I accelerate or decelerate, is less shock to the crankshaft, camshaft, and ip.