Cav we had some 680 blocks that were a throw away.
On the left side it’s accessible to see the bulges adding metal in the region of the head studs.
The block would split along a line approx at the bottom of the studs starting from those bulges and eventually extending bulge to bulge, simply cracking along a dotted line.
I guess engineering design was more years of experience whereas today a computer would do finite analysis and extra metal/thickening/finning would be added where necessary.
Looking at those heads brought back memories of crack repairs in that thin area around the injector.
Had many DC3 flights struggling with a 680 head in my hand luggage.
cav551:
I reckon you are correct, the AV 505, 691 and 760 dry liner engines all had a nitrided crankshaft like the Leyland. I recently had a Leyland 600 which had pulled one of the 3/8 head studs which needed a special stepped stud to be made in order to repair the block. The ‘big’ Leyland head is also noticeably heavier to lift off than the equivalent ‘big’ AEC one. I am about to tackle the problem of an AV590 which has sheared three studs in the block, two of which are already stepped. The bit about depth in the block reminds me that the 470 studs were buried quite some way down in the block, which also contributed to the overheating issue due to extension of the stud when warm.