Ok, so I just picked up my car from the dealership and had the long block engine replaced, with heads, along with the two front cat converters under warranty. The engine damage was caused by the ceramic sand particles from the cats being 'sucked' into the engine. My question - am I to assume that Nissan has rectified the issues with the original engine and cats? Or will I still need to be concerned with timing chain tensioners and the cats failing again?

Also, is there any difinitive reason why these cats failed?