So tell us about the moments leading up to the failure. Mine is approaching that mileage, need to know what to look and listen for.

It was business as usual - except I heard some whistle from the engine bay, as if it were some belt or something... I popped the hood, listened... it wasn't hissing, like from a vacuum, nor it was belt whistle when I was up close... it did sound like a sharpening stone, the kind that rotates and you sharpen a knife - the tone was rather of a higher pitch, as if the knife was of a smaller statute... As I realized in hindsight, that was the timing chain cutting through the last remnants of the plastic guide... About 45 miles the car sounded like a tractor but sitting inside I had no clue - it was rolling fine, accelerating fine, no messages on the board... The passer-bys kind of flagged me, so I rolled the window down and that's when I heard "tractor"... while my slow brain was trying to apprehend what was going on, the dash lit up with some scary messages, and I started to pull off the main drag into some parking lot - as soon as I stopped, I just shut the engine off... it was off since that time... The engine is apart now, and the mechanic says that it might be better to get a used one and slap it in... it might work with normal engine, but stupid me got myself a rare breed... lol... me and mechanic are still talking about it... sooner or later, something is going to give... either we will get it fixed, or i will sell it as it is....

the car will be a classic someday as they only made about 3,000 4.6is's, so if it were me I would go for an engine rebuild.

hahaha... by the time the car will be classic, i will turn into antique!!! but I am still debating, as wife wants a fresh ride, and she is eyeing up a 2010-2013 3-series... At this rate of financial downfall, I can only lease, and I am looking into ED leasing options and into taking over a lease with a lot of available miles (she drives a lot), looking into swapalease website...

nothing is carved in the stone yet...

This maybe a foolish question but did you ever get ahold of Alpine M3 who was parting out the 4.6is. He was last active in June.

I tried to get hold of someone who was parting a 4.6iS on this forum, but i have not heard back... :(

just tear the heads off, check for piston damage and just repair the valvetrain if the bottom end is good

A leak down test of the cylinders will be way easier than pulling the heads of for starters . You might be lucky and just need new chains and guides .

And the 4.4 engine might work out as the capacity is only 25 cc - ish per cylinder less , use all the 4.6 manifolds etc . On the other hand you might blow the 4.4 quickly due to overfuelling but a remap of the ecu might work if you find someone who knows the figures to detune your ecu .

The diagnosis is a bit loose, how did your mechanic come to the conclusion that the engine is toast? If it is only the chain and the cover then I'd go for a repair. I guess he is thinking the sump needs to come off to clean out the debris? (Then you'll need to reset timing. In all a fairly involved bit of wrenching.) Why does he think the pistons/valves are bent?

If it is indeed a goner then I think Slick's approach is the most cost effective one with an assured outcome. I.e. Swap the motor, brain, cluster and engine harness (from th same donor car obviously). Then recode the electronics in your to match.

oldschool v6 nissan valves touched pistons> no piston damage