Must_Have_Z

If you don't use stock, which are perfectly fine, you're just paying for a fancy name. Stick with OEM.

AzDave47

How did the rocker arm bearing fail? If the end clips fatigued and the needles fell out, that is the known "07" failure mode. I think, maybe incorrectly, that was a warranty item.

Katech is very familiar with the valve guide problem and has seen that problem on many engines that came to them as has WCCH, where Katech sends the heads for new valve guides. They are one of the data sources for Hib Halverson's article on LS7s that discusses valve train failure and other problems. See the current thread https://www.corvetteforum.com/forums...ty-issues.html Post 11 for the link.

MTPZ06

Wow...blast from the past.

As to rocker arms...sometimes things just break. Nothing is indestructible. But in general, OE rockers are very reliable outside of a bad batch in 2007. At least a rocker arm failure doesnt trash a $15K motor...count your blessings, and make sure your heads are set up right.

Guide wear...one word "concentricity". **** poor machining at Linamar, GM's subcontractor for cylinder heads. Guide to seat runout can be way beyond tolerance even on brand new heads sitting on GM parts shelves...this eventually leads to premature guide wear. Can there be other contributing factors here...sure, but everything compounds off of improper machining/assembly from the beginning.

As for OE rocker arm sweep...with properly set up heads (guide to seat concentricity), keeping the lift below ~.630, one can achieve an ideal wipe pattern with OE rockers. OE cam lift is .591/.591, so yes an ideal wipe pattern can exist in a bone stock car, provided the heads were competently machined.

MikeOC

Sorry, it was late and I was far too vague and I worded it poorly. I know Katech still recommends the stock rockers most of the time.

I should have said something like, maybe Katech has some new thoughts on the service life of the stock rocker bearings or that there is a slightly wider range of production run that is the effected by the bearing failure. Since it's 9 years after they posted that, my main point being it seems to be a bit unfair to just jump right to "Katech is covering for GM!"

AzDave47

When I did my HCI build in 2016, I had WCCH do my heads based on Katech recommendation, which included new OEM exhaust valves, PSI 1511 springs and OEM rocker arms, so Katech was still happy with the OEM rocker arms in 2016.

MikeOC

I'm (attempting) to say to have a rocker bearing failure on an '06 with 74k mi and then say therefore Katech is covering for GM is a bit of a reach in my opinion.

MTPZ06

Agreed...quite a leap.

Spzany

MTPZ06

Actually they have...open their article posted in this thread: https://www.corvetteforum.com/forums...post1594982862

AzDave47

Even GM admits the the rocker arm bearing failure problem in '07's and ?? maybe late 06's. I don't have the specific GM TIL that specified that as I have an 09. That failure has not happened (as far as I know from being on this forum for 7 years) on 2008 or newer OEM rocker arms.

Katech knows the guide failure issue is a vendor machining issue and have customer heads sent to WCCH for proper guide replacement. They are smart enough businessmen not to call GM out publicly, but make sure their customers get the heads fixed properly.

Spzany

MikeOC

MTPZ06 linked you the head discussion and as far about the rocker bearings, Katech mentioned it in this very thread.

If you would really like answers (if I had a failure I sure would too) it might be better to ask if the rocker bearing failure could have made it into some '06s or if new failures had made themselves known over the past 9 years rather than a more acquisitory tone, people will respond better.

Katech_Zach

I'm not sure where you're getting your information. I wrote an article about the valve guide wear problem that was published in The Shop magazine. It actually shows some findings that contradict GM's claims of affected model years.

AzDave47

GM changed how the needle bearings were held in or changed materials. I may be wrong, but I believe the needle bearing failure was covered by GM under warranty for cars in that 2007 era. I presume they were replaced by the newer units that are in all the later model cars.

Also regarding valve train issues, GM also did a running change on the two-piece sodium exhaust valves at some unspecified time during 2008 production. They have not been particularly forthcoming on what and when the changes were made to limit customer claims (not great customer service for us).

And since you are somewhat new to the forum, many members do not believe the current OEM C6Z exhaust valves are good and decide to go to stainless solid or hollow exhaust valves and stronger springs when they have the heads done to take care of the valve guide issue. Others of us do believe the current OEM exhaust valves are good and prefer the light weight valve train for our LS7s. Arguing one side or the other will get no one any further than the argument for run-flat tires or non- runflat tires or what is the best/fastest Z06 color..

Katech_Zach

Actually, we did in 2012. https://www.corvetteforum.com/forums...cker-arms.html

AzDave47

Thank you, Jason. I had not seen that article, but having done business directly with you, I understood that was Katech's position and have tried to accurately portray that in this thread (and a few others). I will be running my HCI build at the Mojave Magnum April 15.

MTPZ06

Pretty sure it was a bearing retainer cap issue, but it just affected a ~6 month date range. Beyond that though, anything can fail...but certainly nothing of epidemic proportions with respect to OE rockers outside of that early-to-mid 2007 date range.

Unreal

Everything can fail, and has failures. The failure rate of OEM rocker arms is crazy low compared to aftermarket ones. So if you want good, reliable, light, and good valve control, stick with stock.

Michael_D

There's no way I'd use anything but stock, UNLESS I had reasons that demanded a roller-tipped rocker, or I needed a lash adjuster. Out of all the different brands available, I prefer the Crower system. I do not like aluminum. Too many broken rockers over the years, and guys don't like losing races because their car won't run. I've never seen a broke steel rocker.

If it's ain't broke, don't fix it.

long_tall_texan

Spzany, hope this helps give you a bit better understanding of the overall issue...

Here is the most thorough explanation of the big picture of several factors that lead to the guide wear problem. It is a lengthy read, but it pretty much covers all of the known failure/wear points.

https://www.corvetteactioncenter.com...-engine17.html

After a lot of research myself, and pouring over tons of forum discussions on the subject, I decided on a plan for my 2007 Z06.

1. Replace all 16 guides
2. Have new valve seats cut in heads that are concentric with new giudes
3. (might as well mill the heads 0.030" wile I've got them at the shop. A little free HP never hurts, right?)
4. Replace all exhaust valves. (2006 and 2007 models had a potential failure where the tip of the valve is welded on. Better safe than sorry.) I chose to use Ferrea F2042P hollow stem exhaust valves.
5. Replace LS7 rockers with Yella Terra YT6670 roller tipped rockers.
- Roller tipped rockers eliminate any side loading of valve, which could cause increased guide wear.
- LS7 rockers with trunion upgrade likely would have been fine, but I chose to eliminate side loading as much as possible, regardless of how small that side load may be with OEM rockers.
- Yella Terras come with an extra thick valve cover gasket to offset valve covers just enough to clear the rockers. Or you can add an aluminum valve cover spacer. I chose the aluminum spacer.
6. Replace all Valve springs. YT rockers are heavier than OEM LS7 rockers, so stronger springs are needed. I went with PSI 1511.

BTW, I kept the stock LS7 Cam, but would have
​chosen the same path with a cam with 0.630 or less lobes. Above that, may have had to make a different spring choice.

Edited 2/20/18 - corrected the exhaust valve part number that I used.