Atomarc - What actually occurs is compression of the poured babbit. It is the softest part of the rod. The poured babbit is thicker than the babbit in the insert bearing, which has a steel backer and doesn't compress as easily. With the insert bearings, the rods will actually elongate (stretch) when subjected to sustained operation at high rpms.
The way to avoid this problem in the 216 is to keep the rpm down, preferably under 2,500 for sustained operation. There are guys here with over 100,000 miles on the 216. But some have also ran them hard enough that they only got 50-60,000 miles out of them.
