The failure that Laurens shows in his photograph above is, I believe due to the fact that the timing sprockets appear to be "Sintered" or produced by a process known a "Powder Matallurgy".
In this process metal powder is compressed into a mould and then heated to allow the metallic grains to fuse together. The process has to be very closely controlled to ensure maximum strength in the finished component and if the powder is not properly fused together this can result in the final component having less than the required strength.
I recall some time ago people were experiencing failure of the keyways in the pulleys for the same reason.
The following website has the details :-
https://www.pm-review.com/introduct...tering-in-the-powder-metallurgy-process/regards
Keith
