Hi ericandchi many thanks for all that information much appreciated, this is a complete & total learning curve for me, so I am very grateful for all the help and Guidance .

I had the Crankshaft professionally rebuilt, I do not possess those sort of skills or tools I’m afraid, therefore unfortunately I only have the pictures that I managed to obtain & a verbal report that the Crankshaft was fine to be re-built.

I’ve included a few extra pictures showing how the Bearing Cage is fractured & some damage to the Cage itself if that provides any sort of clue.

Sorry I cannot be more helpful or forthcoming, I am writing this Rebuild journey somewhat after the event with the hope that the images may provide some help to those who are in the same boat as me so to speak and also as an aide memoire to when I do my NSR250 88 MC18.

Once again many thanks, hope the pictures shed a bit more light on what might have happened.