OOh. I wanted to go to the CSM. Never happened though. I have a though on the defective valves though. If they are failing, replace them with better ones... Factory valves are generally not picked for longevity unless you are Cummins, Cat or Lister...

I do find it interesting that the failures on two were 200 miles one 700 miles and one 4,000 miles after work but of course correlation and causation are not the same. Otherwise one could conclude that ARP stud replacement or replacing rockers (BTW were they replaced with the new version?) or adding the weeks kit were causes.

I tried to follow this logic trail, but it failed for me.
1) Without being there to know PRECISELY what work was done, by whom, and following what procedures, not only causation fails, but correlation as well.
2) If I were to assume that major work had been done, the most common major work needed is timing belt change, and associated maintenance. This, if proven true, could possibly be the one thing that these four examples might actually share. Would it not then be more reasonable to look to human error, or deliberately cutting procedural corners, while performing the re-timing sequence? I don't understand, when, having slippery logical footing already, one would not slide, but jump down-slope, to attempt hanging the blame on ARP studs or WEEKS kits. Both ARP studs and WEEKS kits are on dozens if not hundreds of CRD's that haven't had valves break for, many millions of combined miles. Now people who make mistakes while performing complicated procedures, including the mistake of having someone else who makes mistakes, do the work, is immensely more common.

The one valve failure under the previously broken rocker makes sense on one level maybe the rocker didn't really do its job.

I do personally wonder if a speciific combination of rocker and arp studs could even contribute. I am fixing to either replace just ARP or ARP and head gasket depending on what i find on teardown. I was planning on replacing rockers also with either scenario. Is the design so tight that further compression of the head gasket with ARP s and new rockers that are not worn could essentially reduce clearance enough to be out of tolerance?

Far more likely that the wrong thickness head gasket was used. Overtorquing the ARP studs is possible, but that by it's self still wouldn't bury the valves into the pistons. It could, however, compress the head gasket a tiny bit more, but not nearly as much as using the wrong head gasket.

I would say no, since the valves also have wear which would increase it some compared to new engine. Are the new rockers actually oiling better? If the ARP s and rockers were being replaced prophylactically I can see this as a very remote possibility. If they are being replaced after broken rockers I would personally expect sometimes the valves were unknowingly stressed or damaged. Maybe I shouldn't fix the head gasket leak and just run it till it failed catastrophically!!!! LOL! I am afraid to touch it and spend all the time and money then have it fail in 200 miles! Aren't we all? Thankfully I have overcome the fear and am proceeding with the repair. If a brand new head did it I will take my chances.

I will report after 1,000 miles if I make it that far! Hopefully you will still be reporting many thousands of miles later.
I wish you the best of luck. And wish you to make your own luck. Do things in correct order. Double check things as you go. Take notes when you have to consult the manual, or, heck I guess if you have a smartphone you can have them right with you. If you get distracted or have to take a break, back up a step or two, and go through what you did up to the point you left. The time you spend doing this will be a heck of a lot less than the time you could spend having to go way back and install some small but very important part that got overlooked. (Like getting an engine completely rebuilt and assembled and realizing that wonky looking washer over there is actually the crankshaft oil-slinger)

ok back on this thread again ,, so my understanding is that exhaust valves are made in VM factory in Istanbul Turkey , i think for the people that experienced these RARE failures (broken valve) , I think it is worth contacting the manufacturer and sending them faulty valves for inspection , because they make them so let them do the testing and send us results , i would really love to see their side of the story

anyone can google "valve failure", but this one isn't infested with pop-ups and advertising (and it's free)
https://www.rroij.com/open-access/failu ... ?aid=44965

Machinist reported that he milled the head to eliminate some surface warp around cylinders 2 and 3, as well as slight fire-ring impression. He cut a little less than .003. The valve seats were not concentric with valve guides on 2 and 3. he recut the seats so they're concentric with the guides, and in coordination with the surface milling. From removal, bolts for cylinders 2 and 3 were not correct torque, significantly looser than the front and rear cylinder head bolts. So he described a scenario where the seat/guide misalignment could cause lateral forces on the stem/structure of the valve during both opening, and closing, leading to long-term and ever increasing fatigue. I though it was worth posting here and see what you make of his theory. I like his thinking. if true, and if similar warpage occurs on other crds, it could explain at least some of the valve failures.

NOTE: if someone has already posted this theory, then my machinist agrees with you, and so do i

The scenario would be:

1. the fastener begins to fail or was never properly torqued
2. the head over time begins to warp due to uneven clamping forces, heat etc
3. the movement of the structure of the head changes the position of the seat relative to the valve guide (he called it "sinking")
4. increase in valve misalignment induced lateral force on the valve stem during opening and closing
5. valve suffers increasing fatigue and eventual failure.

Have fun!