long_tall_texan

I was considering gettign a set of Yella Terra 6670 rockers for my 2007 Z06 to put on it when I tear down to fix the heads this winter. In researching, I ran across mixed information on them when used in the LS7 application - some praise, some reported failures... But really, if you want a roller tip rocker for LS7, Yella Terra and Scorpion. Yella Terra seems like a more respected brand overall, so I wanted more information. So... I decided to go to the source. I emailed Yella Terra directly from their website, and messaged them through Facebook. I got a return email from the US Product Development Manager. Thought I would share it with y'all to clear up any mis-information that is circulating on the internet... I was asking specifically about LS7 rockers, but since LS3 and even LS1 were mentioned, I thought it would be good info to share with all... Not trying to start a flame war by any means, but anyone's personal experience with 6670 rockers on stock LS7 heads is welcomed.

I basically asked if there was a way to tell the difference between the first generation LS7 rockers, and the new second gen rockers that I had read about in numerous forums that were "fixed".

His Reply:
I received this inquiry from our factory Reps in Australia. Let me try to set the record straight for you.
We have sold literally thousands of sets of our YT6670 rockers, with no issues.
In fact Corvette clubs across the country advocate the use of our YT6670 rockers to eliminate the premature valve guide wear problem that is rampant in all the LS7 cylinder heads with factory, side loading, sliding tip rockers.
It is true GM has two foundries casting their heads. There are unfortunately some subtle differences in the finished castings. They are very minor. A couple of years ago, two different LS7 engine customers noticed a slight offset in the nose wheel contact points on their LS7 cylinder heads. Because they each made a request for us to look into this, we gathered up several LS7 heads and observed the nose wheel contact areas on them. A few of them displayed this parody. The worst of the lot required less than .030 of an inch offset to center the wheel on the valve stem lash cap. Here's the kicker. When we removed the lash cap the offset was reduced to less than .010". The large beveled lash cap gave the appearance that the nose wheel was much farther away from center than it actually was. Because we strived to engineer the very smallest nose wheel in the industry, the appearance of the contact points is magnified on the rather large lash cap. This discovery along with the evidence that we had never had an issue or complaint of improper wear patterns nor any nose wheel or valve stem or lash cap issues led us to keep the original rocker design. As usual, the information in the forums can often be tainted by folks who simply are misinformed. We continue to sell hundreds of sets of our YT6670 Ultralite rockers with no complaints from our engine builders and DIY's.
I hope this answered your concerns. If you have any other questions don't hesitate to get with me.
Remember.... Soak your rockers in a tub of engine oil for an hour or so before final assembly to ensure total oiling and full protection during the initial start up and lifter pressurization period. Failure to do this on any fully rolorized caged needle bearing rocker package is the leading cause of premature wear. A dab of white lithium placed on each valve cap and pushrod seat is also a great wear preventative. Gerotor pumps do not lend themselves to priming like their predecessors.

My follow-up question:
Was there any other known/identified problem with rocker, bearing, or tip roller over the history of YT LS7 rockers? Seems like I have seen a few posts here and there that YT rockers had failed in the early adopters of your LS7 rockers. But again, as you said, you have sold thousands of them, and there are only a very few claims of failures, which does not indicate a problem with your product necessarily. More likely that they were run outside of recommended spec - higher RPM, very high lift cam, or simple an error in installation or proper push rod length. Way too many variables. Just curious if y'all have had to make any corrective action over the years.

His Reply:
Never!!!!
The only recorded failures have been the lack of knowledge of the installers not properly oiling before installing, misplacing the half moon adapters, pulling down the pairs unevenly, improper torquing, all novice mistakes. Unfortunately, we can do little about that. I handle all the warranty and spare parts issues in the US. I provide less LS7 parts than all others put together. We had some problems with our early 2008 LS1 rockers that were designed as a stock application replacement being used on high spring pressure and/or severe ramp speed cam applications instead of the required design rockers we make for that application by users who didn’t want to spend the extra bucks. That’s about it. Some of the highest regarded engine builders in the country rely on our rockers for simple street applications to monster engines with spring pressures over 900lbs. YT rockers have been in production since 1962. As a valve train engineer, and an engine builder for many years, I have been on the ground floor design team for several rocker arm manufacturers including Crane Cams and Yella Terra. This company has the utmost respect for its clients.

My next follow-up question:
Thanks for the info again. Here's another post that just came up on corvetteforum. I almost wonder if people are trying to run the LS3 rockers on LS7 and having problems?

Then I quoted these 2 posts from earlier in this thread.

His reply:
Same old same old. People that think the rockers should jump out of the box and fit themselves to an altered engine. Tony Mamo is one of the most respected EB’s in the industry and one of best clients, not to mention he is one of my best friends. I have never had to machine the stands, shims are included with each kit and adjusting the geometry on a modified platform has always been the responsibility of the EB, as is the hydraulic lifter preload. The LS3 rockers are a totally different design and will never fit the LS7 heads. Another problem is running the GM version on a non GM head. Happens all the time. Folks don’t do their homework and discover we make different sets for different heads. The writer who answered the first guy is confusing the redesign on the LS1 rockers with the LS7. We always strive to improve our products. As time passes we sometimes improve an existing design because the application requires it. The changes are most often very subtle and in most cases impossible to see.
---------

So there you have it. Straight from the source.

long_tall_texan

Additional Discussion in this thread starting at Post #29...

https://www.corvetteforum.com/forums...post1592731592

cwylie

Whats the max RPM recommended with these at .650 lift?

CTD

I've no experience with the LS7 configuration & the YT's. I do have experience with YT's in LS1 & LS3 stroker cathedral configuration. I have experience with the mention individual who is most respected. None of these experiences are positive nor recommended on my part.

I would suggest further research, no YT's in my current setup. Don't limit yourself to CF threads.

long_tall_texan

I definitely didn't limit myself to CF. Looked elsewhere too. Have not seen any LS7 rocker failures. Have seen something about possible 2 versions of the rocker. I know what to look for, and if, when I install on my Vette, I see that problem, I'll take it back up with Yella Terra directly before putting the valve covers back on. They will be perfect before I start it the first time.

Brandon619

This is good information, with Yella Terra acknowledging what's happened in the past I believe there is a large margin of error when people install their aftermarket rockers. I am in no way an expect on this subject. When installing a set of YT or any manufacturers roller rockers there is a couple of factors that need to be considered. The rocker geometry and the height of the rocker is top priority when setting up your rocker wipe pattern. Correct pushrod length and lifter preload are also play a key factor on proper rocker geometry.

long_tall_texan

For anyone that has direct experience with any Yella Terra failure, please give us a little more information.

1. What motor? LS1, LS2, LS3, L96, LS7, LS9?
2. Cam? If so, what was max lift?
3. What heads were you using?
4. When were rockers purchased? Date...
5. When did they fail? Miles...
6. Pics of what failed if you have them.

I'm not arguing or questioning if there was really a problem with the rockers. I would just like to gather a little more data and see if we can see a trend of what may cause the failures

Tony @ Mamo Motorsports

I don't have time to get into a lengthy detailed response right now so I will do my best to be brief and to the point but also convey the information I believe is most pertinent here. I have known the current management of this company for over a decade (family run business for the most part)....all good people to know and deal with. I had met with them back when I was at AFR and encouraged them to build a lighter weight system made specifically for HR valvetrains that were much more common in the LS engines than they were previously in 23' SBC performance builds. Most if not all aftermarket LS stuff at the time (including Yella Terra's existing product) was too heavy and created valvetrain instability (float) and engine performance suffered greatly due to poor valve control (once you lose valve control your done making power). Long story short, the new management (at the time) listened and decided to build the 1st generation Ultralite which I believe was launched around 2005....2006 at the latest.

To sum it up, they worked great.....perfect valve control....much better geometry than stock....big reduction in guide wear but the bad news was there were a few isolated failures at the time. They beefed them up a bit more around 2009 -2010 which became the 2nd Gen....failures were reduced dramatically but a year or two later they made another strength improving change in the construction of the rocker and these became the current and most dependable version of the rocker (what most refer to as the 3rd Gen design). Note all of this relates to the cathedral head rockers.....the LS7 stuff was and is different and they never experienced some of the problems of the 1st gen cathedral design did a decade ago.....clearly the company got a better handle on the design of the rocker bodies and it shows in the reliability of the current product but let's face it....some people can break anything given the wrong application....wrong springs....piston to valve issues causing light mechanical interference....I can go on and on. There must be a dozen ways to break a rocker arm with the wrong application or the wrong parts or simply not building the engine properly.

Every LS motor I have built for myself and my customers since 2004 has ran these rockers. I have sold hundreds of them to my customers....my direct and vast experience has been overwhelmingly positive and they are my rocker of choice for most HR and SR LS applications. They just finished building a system for my recently released Mamo Motorsports LS7 and LS3 heads (both utilizing TFS castings btw). I run them in ALL my personal engines. Im not sure what else I can offer in an attempt to make (the OP) and anyone else reading feel more comfortable but I wouldn't hesitate a minute to run them and in fact for me, as I have already highlighted, this is the go to product of choice, rocker arm related, for all my builds (certainly all my LS builds).

Full disclosure....Im friendly with the principals of the company.....I like and believe in the product and have used it successfully more times than I can count, and Im their west coast distributor so yes I stock and inventory their product and I make money moving selling their product but I do so knowing Im actually helping everyone I send a rocker kit to....I can sleep just fine at the end of the day.

In fact I will elaborate on this topic even further and state you couldn't pay me to run a stock rocker (trunion upgrade or otherwise) in an LS performance build. The geometry is horrible (the wipe pattern is a square when ideally it's a narrow rectangular patch) and they scrub over the top of the valve (no roller wheel) which sideloads the valve stems. These sideloading forces ultimately wear out the valve guides in the heads creating an hourglass shape which now does not control/position the valve properly (the valves will now "wiggle" in the heads). This leads to oil consumption issues and naturally it negatively impacts the valves ability to seal properly on the seat angle of the cylinder head. The stock rocker arm geometry is really bad with .600 plus lift....in fact I encourage you guys running stock rockers (or considering running them) to actually check the wipe pattern and look for yourself. They are just out of their element in any serious LS build, especially with the higher spring pressures associated with most performance builds (all of this further aggravating the wear and sideload forces being generated). Do stock rockers technically work....yes....certainly they will open and close your valves but choosing to use them comes at a cost I'm not willing to live with. A lightweight aftermarket performance rocker with better geometry meant for higher lifts and designed to put up with the additional spring pressure and RPM (and that is fitted with a roller wheel which is a huge perk) is the right tool for the job IMO.

Guys Im clearly passionate about this hobby but also passionate about this topic because IMO there is alot of bad information out there. I can't count how many folks I have helped and how many motors I have built with them over the years....and while I have had a couple of folks have a problem (never in a motor I personally built btw with the exception of a single Gen 1 failure), you have to realize that no product has a perfect track record and anything can and will break in performance related builds....what you want to steer clear of are products that have an epidemic of failures and that's clearly not the case here.

Good thing I didnt have time to post a lengthy reply.....LOL

Regards,
Tony

PS....The real clincher for me....even if I personally experienced a single rocker failure with my ride....I would rather be inconvenienced for an evening and get an AAA ride back home on the flat bed then install a stock rocker knowing Im going to dramatically shorten the service life of my heads. If a rocker breaks it really is just an inconvenience guys....it's not like a rod failure where it trashes your 15-20K engine. You will spend alot more money and be much further inconvenienced when you have to freshen your heads because your valve guides are toast. I hope some of you find the time I just invested typing all of some value.

Brandon619

Tony is the man when it comes to heads, I will be running Yella Terra Rockers per Tony's recommendation on his 223cc Sportsmans heads.

long_tall_texan

Thank you Tony. I DO appreciate your response, and the time you took to give us your "brief and to the point" reply.

As for my concerns, I do not have any. After talking with Roger Vinci and Dan_the_C5_Man and seeing pics of the "problem" LS7 rockers, I feel very confident putting them in my Z06. If I see the alignment issue when I install them, I'll contact Roger for the corrected offset versions.

Looking forward to running them myself.

Arkus007

Well I have on here that failed check the pictures out. Look closely at the pictures, you can see that one of the push rod cups has sunk or stretched causing excessive valve lash at about .200" plus causing rough running and misfiring.

long_tall_texan

Please provide additional info. What is the cam lift used? What valve springs were used?

Tony @ Mamo Motorsports

Spoke with this person earlier today....

The rockers are 10 years old with a few thousand miles on them but he is running excessive spring pressure (480 open). Im sure that contributed to the problem he was having although you just never know.

They are rated at 400 lbs of open pressure but I routinely run 420 - 440 on my more aggressive higher RPM HR set-ups.....less on stage 2 and milder combinations

480 is simply more than you need for these rockers as the rocker body (what's actually pivoting on the fixed fulcrum) is very lightweight.

A newer kit would be a stronger design also.....they did a redesign of the rockers bodies like 6 years ago but the issue experienced here is very uncommon.

-Tony