One thrust washer for crank was fitted the wrong way round. It wore in to the crank and ended up with 5 mm end float. This caused stress on the camshaft via the chain an induced wear on the camshaft slot causing end float of about 5mm . Eventually this end float was sufficient for a cam follower to drop into path of lob of camshaft and seize the camshaft. At this point the camshaft sprocket was ripped off and chain snapped. Engine has only completed 10k since rebuilt and sounded fantastic with no indication it was about to spit its dummy out. Engine out and off to the engine guys to see what can be saved :-)
