The plastic guides of the timing chain go brittle from the heat and can break. A broken guide does not guide the chain, the chain slaps, and the valve timing can shift.

The early sign is a rattle audible at a cold start from the front of the engine. If the chain jumps, the valves and the pistons meet, and that is already an engine rebuild.

The condition of the guide can only be seen with the engine apart, so the rule is that whenever the upper timing chain cover is off, the guides have to be looked at as well. That comes up during the repair of the coolant pipe running in the V valley and of the alternator bracket, because those require opening up too.