So Gordon,I ran this photo and others past a few wise engine builders. Turns out the radius, seen in the background journal, has some harmonic chatter marks in it from when the crank was cut and polished. These are machine tool marks. If you look at the other side of the fracture, it begins at the root of one of the chatter marks in the radius. Stress risers are always a problem, no matter where they are.
Not yet. However if you got high enough engine speeds with good rods and pistons, you might set up some nasty vibrations. MANY years ago it turned out to be possible to crack the main bearing webs out of GTA blocks without much obvious damage to crank, rods or pistons. Naturally, if the engine ran like this more than a few seconds it became aluminum scrap. Enough were shut down when the oil pressure dropped to diagnose the failure, and Alfa (Autodelta) redesigned the blocks, both race and street, with different webs.
With the older blocks the rule was not to exceed 7500 rpm for more than absolutely necessary or you might suffer a failure. I believe these were from accumulated stress build up, as the previously stressed blocks that showed no sign of failure, would fail later in racing at lower speeds. Early on, until the "new" blocks arrived, we tried both steel and aluminum bottom end cradles. The machine work was daunting to both fit these and make them work at that time. Six bolt main fastening was the extreme version like the GM Chevies. This was a heck of a job, and I have not seen one of these blocks that has survived, though one or two are probably out there. The whole bottom of the block was re-engineered by guess-and-by-gosh.
It is possible this was caused by the light, 2 ring pistons, and lightened rods. The Autodelta GTA cranks were left as massive as possible, as obviously, any flex was the end of the story.
I don't really know the numbers, but can get the time frame at 1966. The rear main got a rework with the 101 1600 Veloce engines, but the upper web was somehow stiffened about late 66 to 67. The Autodelta replacement blocks were unnumbered. I wish I had thought at the time that these details would be of future historical importance, and carried my Cannon 35 mm around with me the way I now carry my Cannon digital camera everywhere. You might send Karen Dale McGowan, <[email protected]> an inquiry about this subject as she was with Ron Neal at PROTOTYPE engineering after the AUSCA years. Ron was still the master with these engines at the time Karen worked there. She may have more information, but probably, like me, no photo's. I will forward these posts to her E-Mail as she may have comments that differ from my own.
I hope this helps.
This is probably of no help, but examining the webs in some engines I have had apart, whatever the difference, is not easily apparent. Perhaps if I had seen two, side by side, it might be noticeable. The basic architecture must be very similar.
As this change was not limited to just the GTA blocks, that would seem to suggest all late 1600 and all 1750 blocks were strengthened in the web area. Perhaps weighing a stripped early 101 1600 block and comparing that to a later, but seemingly identical 105 1600 block, might show a weight difference. I don't know.