I suspect they are two different problems.
The rounded teeth are sturdier, as they don't tend to crack as much at the bottom, esp with an old belt, as square teeth can (less overturning moment at the bottom corner), and they also reduce the tendency of a square tooth corner to "trip/catch" on the top corner of the square teeth on the cam pulley.
The mechanical tensioners tend to allow belt slack when the engine is turned backward, letting the belt to leap over the cam pulley teeth en masse, as one group at the same time. I don't think the rounded teeth prevent that. They are better in the long run otherwise.
That's my take on it anyway.
When rebuilding an engine from the ground up, you do have to install new crankshaft thrust washers, oversized if necessary. I've known a few who forget about that when putting new rod bearings it seems.
1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27
previously owned since 1964:
62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
Last edited by Del; 03-03-2017 at 05:49 PM.