Who cncs the OEM ls7 head
 

I don't want to appear to not answer your question but you might as well ask if there is a God. There are numerous threads that discuss this subject to death, if you do a search you will find plenty of reading.

The generally accepted explanation is that Linamar, Ontario, Canada was the supplier charged with providing the heads. They apparently did not drill/bore the valve guide bores concentrically; this created a geometry problem that causes premature valve guide were, some as early as 3,000 miles (see my related thread). This was admitted by Chevrolet, who claimed the problem was rectified in 2011, however there are failures occurring in all years.

Again, read the threads, there are also comments about oil starvation due to excessive heat due to the construction of the exhaust valves, rocker geometry, cam lift, etc. There are those on the Forum that have purchased brand new replacement heads from Chevy, had them checked and they were bad, from a concentricity perspective.

Hope this helps.

Wow a VIP? Sometimes I think I'm important but then I hear about VIPs and remember I'm just a lowly peasant.

I would not know and this is way deeper than I can go on the subject.

My research says there is no 1 single thing that causes the failure, there are multiple problems, the LS7 is a very high performance engine and if ALL is not well the valves will fail just a question of WHEN and there is no certainty to that. Some go lots of miles no failures others in a short time frame. You need to look carefully at yours and decide if its okay or if it is time to do the heads. On mine personally it has about 24,000mi and I have done what I call maintenance updates, upgraded trunion bearings and much better pushrods, to it to extend the life of it. If I keep it I will be doing heads eventually if not I may sell mine at the end of this year in the mean time I have run a dial indicator on the valves and have less than .0035 movement at the retainer and am satisfied it will survive for the time being.

The only thing I have read after tons of research and cannot remember where it was but it said 2 different setups used over time at Linamar which I think but am not certain was in reference to the non concentric machining problem that occurred. That is all I have ever seen remotely connected to the actual CNC program.

We did not do any production machining for LS7 cylinder heads.

Dood.. C'mon man.. This has been explained ad-nauseum.. I hope Jason has better things to do.. :cheers:

You're right, it's been discussed over and over here on the forum, but I'll assume 427V8BB is new to the vehicle and I'll give you my thoughts. What I don't want this to turn into is yet another debate, so I'll post our findings and be on my way. If you want any more information feel free to email me at jason@katechengines.com

We have not directly attributed dropping valves to worn guides here, but we have seem some pretty severe hourglass shaped wear and I can assume that given enough time to wobble around in the head it could ultimately lead to valve failure. I've attached the article I wrote regarding valve guides to get you up to speed.

Maybe the VIP is the same one that said they started doing 100% inspection of the Linimar provided heads in early 2011, yet brand new heads from the factory provided in 2013 have had the guides not concentric with the valve seats by more than the GM specification. One GM machinist/engineer said that could not be the case because GM uses the guide to do the valve seat. That may be what GM does internally, but Linimar is "modern" and uses CNC machines to do the seats, not using the guides as the tool "guide" to center the milled guide seat.

Linimar also provided all the C7Z06 e-difs "ready to install" to Chevy. They just short filled the difs on the oil, which is not on any dealer list to do a PDI check of dif oil level. Quite a few of those e-difs failed in less than 5K miles.