Over the years ive seen loads of bits sucked into engines ....jubilee clips , heads off screws , small sockets ,turbo impeller nuts , snap on screw driver bits , all left in the inlet tracs .......destroys engines for sure .
Metal fatigue ........ yes it happens .....on a relatively cool valve ......i dont buy it .
Something could of been left in there from the service and air filters ......or maybe not .
The dpf ?? what full deletion ? has it had egr blanked off or any other work done on inlet tract , inlet butterflys ......egrs replaced ?? any work done near inter coolers , something has caused this .......its not just happened .
Ive seen heads snapped off valves when something has got stuck under the valve and seat , piston comes up and gives the valve a clonk and because object is stuck under one side the valve head gets knocked side ways .
Very often what ever has gone through the piston and exits the exhaust normally strikes the turbo exhaust impeller aswell ....... seen tips off glow plugs doing this after passing through the engine ......takes a blade off or two .....makes the turbo do the 'cyclone ' sound .
yes take some more photos of the ports if you could , looks like your in for a big rebuild bill sadly
