This is how to replace all 3 timing chains, guides, and tensioners on a Nissan VQ40DE engine. This one happens to be in a Pathfinder but process is the same for any VQ40DE. This is not a quick or cheap repair but is thousands of dollars cheaper to do at home rather than taking it to a repair shop. Just make sure your mechanical skills are up to par for this level of repair before starting. I would put this at a 6-6.5 out of 10 on the difficulty scale.