So, after reading a bunch on this topic, and listening to people talk about them being warped or cracked or whatever, I can honestly say, that after literally machining hundreds of these heads, I can say that it's like the "occupy movement" haha, 99% of your heads are going to be cracked, and the 1% that's not...and probably 75% are warped, but less than .002", and the other 25% is wapred about .005" or less. That being said, Navistar calls the cracks "micro-fizures"...and says they're ok, and while this might be true, we don't send them back out with cracks...we always cut the crack out and press a hardened seat in the seats that are cracked (not a sales pitch). But I've never seen a crack on one of these motors that actually goes into a water jacket, not one. While the crack can lead to a burned valve, or loss of compression, even if only slightly, it's not like cracks in old school 350 chevy heads, or small block/big block ford heads that are likely to be cracked into a water jacket...these castings are think around the deck surface (much thicker than a 6.4 by the way.)
Anyway, what I'm getting at is of course the vast majority of heads evaluated by a competent machine shop can have some faults, but rarely ones that will keep it from running. Oh, and if you don't think that (10) 14mm bolts/studs torqued to well over 200 ft/lbs will make the head absolutely flat (or at least as flat as the deck surface of the block)...you'd be wrong. It doesn't take that much pressure to "warp" these things by .001-.002". So, from a mechanical standpoint, if the gaskets aren't leaking, and they carefully did it one by one, it should work, and yes, possibly even fix a slight leak, at least for a while. Still not "right"...and I'd still always recommend milling the heads, and much though it is impractical, mill the block to as long as we're talking about being perfect. (I don't think the ford techs at the dealership, or anywhere else for that matter are checking "RA-roughness average" or the surface finish, or straightness after they wire wheel the block's deck surface before they slap the new gaskets on)...and some of these trucks have had 2, and 3 sets of head gaskets on them.
All that being said, I might actually try the one by one approach when I dive into it to change the injectors. Sad, as the one expense that keeps people from doing it "right" is free to me (sorry if that sounds conceded, didn't mean for it to)...but if it works, it saved lots of extra time and work, if not, I'll really go through the heads the way they should be anyway. It worked for lots of other people.
sorry for rambling again...I gotta quite drinking...however this truck isn't exactly helping me with that, lol.
2005 F-250 Harley Davidson Edition
Warren 205/75 Injectors
KC Turbo 71mm VGT
Twisted Diesel Level 3 Transmission/PI Converter
AFE Intercooler/Flexalite Fans/Mishimoto Radiator
Icon 4 Link, 37" Nitto's
SSBC 6 piston calipers
Yukon 4.30's, Detroit Locker
Machining the 6.0: