I wholeheartedly expect to exceed 250,000 miles on the engine in my 2006.
(The only caveats: selling it for a different Xterra or going with the V8 swap instead of doing the timing chains....)
Every engine has weak points. Every engine needs PM. Every engine has wear items that require replacement at some point.
Outside of those factors, the VQ40 tself is a damn robust design. One of the best I’ve owned. FAR superior to the V8 travesty that Rover used in the Disco/RR for too many years. And on par with the beautifully bulletproof m42 4 banger BMW developed.
I define both valves and timing chains as “eventual” wear items. Some might never need touched. Others may require several visits over time.
The defining factors are hugely varied by vehicle history, PM, abuse and use, etc. BUT, no engine lasts forever. And good maintenance will take most modern engines far past the manufacturers projected obsolesence.
I’m just shy of 140,000. It’ll either be a timing chain job or the V8 swap whenever I start to hear the tell tale “whine”.
(The service history of my X, while pretty comprehensive, never mentions TC replacement.)
Valves? Who knows. Most likely never. But if they need done they’ll get done.
As one of our esteemable veteran members said in another thread, “we are outliers”, who care more for our vehicles than the general public.
We define every problem, address every issue, chase each tiny annoyance til the bitter end.
And we ALWAYS open up the engine.