I really do no know what happened. The engine was turning fine and I was reving it up to 6000 most of the morning during a rally.
Oil pressure was perfect.
But one of the con rod bolts came off really easy, so I think that it might have been a con rod bolt that stretched. Incidentally I had ordered new bolts, only to find out (late) that I had ordered the 3/8" instead of the 13/32" which I have on my rods now, so I did not change them.
Regarding the engine teardown I will first see how everything looks like. Fortunately I cought the failure very early. The bad rod is not blued, and most of the debris was in the screen of the
oil pickup.
The filter was brand new The two bearing halves were actually superposed on top of each other. The crank does not even look so bad.
I hope for the best, but if everything has to come off for cleaning, so be it.