Everyone has a theory. I placed powdered metal guides & Ferrera hollow stem valves
in mine and plan to use shaft mounted rocker arms. You can call and ask Chris Frank guy's @ FED or the guy's @ AHP. I've read & seen Tanner replace guides from WCCH and a few other well known shops. Some don't have trouble while others do. As a friend said on Ls1 I have yet to see any other Ls head have these problems with PM guides, and shaft mounted rokers can only help. IMO. Also the factory valves or better said the exhaust valve is generally the problem ...replace with Ferrera valves. Moldstar 90 valve guides is the best but cost $.

 

Thought it needed to be here.


D Morgan......

06-29-2015, 04:41 PM
]After 35 years in this industry I am basing the following opinions on my own experience and feedback from other professionals in the industry who I trust. There is no doubt that people who push their cars a bit more than others will have a higher instance of exhaust valve guide problems. In my opinion people who take there Corvette to the local sports car track on the weekends are much more likely to have exhaust valve guide issues. People who drive around leisurely on the weekends will have far fewer instances of valve guide failure but they are not exempt from such failures.

Causes of valve guide failure in GM LS7

B: Incompatible metals. A steal valve and steal (powdered metal) guide are not compatible metals in a situation where high heat and low lubricity are called for. Any guide material will work but the clearances and oil flow must be managed in order to make the parts live! People ask me all the time if bronze guides are better. The correct type of bronze guide, yes. It’s definitely better. The wrong type of bronze guide would be a disaster and wear even faster than the steel guide! Would a high nickel bronze like the new CHE guides be a better choice? Of course they would because they can live with less oil in a high heat situation, like the LS7 exhaust port.

A: Lack of lubrication. Regardless of the materials being used I feel that lack of lubrication to the valve stem is the root cause of this problem. The tight valve stem seals are stiff and pretty much insure that very little oil will get to the exhaust guide. Great for the EPA and the Catalytic converter but bad for longevity. Granted, these are the same seals used on countless LS engines but, the LS7 makes a lot more power (HEAT) than even its ls3 predecessor. The oil flow might be barley adequate for an ls1- Ls6 or ls3 and never show excessive wear but still be inadequate for an LS7 and cause accelerated wear. It all comes down to the balance of oil flow through the guide and heat. The LS7 obviously has a higher heat condition for the oil flow it’s receiving. That’s obvious to anyone.

C: Too much heat transfer into guide. Too much heat and barley enough oil to get the job done is not a good recipe for longevity! Heat destroys what little hydrodynamic oil wedge is present in the guide by literally vaporizing or burning it out of the guide and off the stem of the valve. This accelerates wear and carbon build up at the tip of the guide inside the exhaust port. The wear and carbon build up then start to creep up the guide over time causing it to taper or “bell mouth”. This taper is accelerated once it reaches the half way point. The taper and guide wear is also drastically accelerated by the non-roller tip rockers arms which drag the valve stem back and forth as it opens and closes. Non roller tip rockers will take guides OUT if everything is not perfect. Once the guide hits about .003 clearance the wear DRASTICALLY accelerates and smoking during engine start up will be noticeable. Is a little smoke during start up a bad thing? Not if you mean to do it! In certain situations, it’s perfectly normal. Every set of LS7 heads I have ever done for a road racer probably smokes a bit on start up because I take a razor blade to the exhaust seal and slice it so the guide gets more oil. My road race heads NEVER come back with worn out guides. I also take those springs off the seals to relax them and lower there tension thereby allowing a higher oil flow to the guide. On all out racing engines we don’t use valve stem seals. Higher engine speeds and more heat call for higher oil flow down the valve guide. Now, I would not do this for street vehicle. I am stating this to prove the point. Each situation is different and the more power you make, the more oil “FLOW” you need in order to carry the heat away from the component. Another factor regarding heat transfer into the guide would be the sodium filled exhaust valves. These valves are a GREAT idea for a truck engines that pulls large loads at a part throttle setting under moderate power levels. In the case of the LS7, it’s not a good choice. It transfers the heat from the valve head into the valve guide at a much quicker rate than a solid steel stem valve. This just exacerbates the previous problems I have just listed above pertaining to valve guide wear.
I really don’t know why anyone would put a two piece sodium valve (of this quality) in a high performance engine that operates at moderately high engine speeds. The sodium filled valves themselves have been the cause of major engine damage because they have broken in two. Sodium filled exhaust are notoriously weaker than a solid stem valve and therefore should never use in high performance engines. There are some aftermarket manufacturers that can produce a sodium filled valve for high performance use but they are quite expensive and in personal opinion, a bad idea! If you plan on increasing the performance of ANY LS engine I personally think the use of both the OEM intake and exhaust valves is just a bad idea with the exception of the DelWest intake in the LS7. The LS7 intake valve is fine.

D: Heat transfer from valve guide through aluminum boss and into the coolant itself may be inefficient or hindered in some way. The following opinion is somewhat debatable but there may very well be a “steam lock” or “steam pocket” in the water jacket above the exhaust ports around the valve guide area. The water jacket is very tall which allows for steam pockets to form so this opinion (although not my own) has some validity! Steam pockets need three things in which to form. Plenty of heat and a lack of circulation in some high spot in the water jacket. The LS7 heads has both. This does not mean its happening. More testing must be done in order to validate this theory.
Some people may disagree with me on certain points here and that’s fine. If any of my statements are proved incorrect, I will be the first to admit it. These are simply my observations and opinions on the subject. Take them for what they are worth. This is something everyone on the net should get behind and discuss. It’s a HUGE problem! There is no debate over the fact that the LS7 engines has serious valve guide problems. These engines are powerful and they build a lot of heat especially when guys take their cars to the road race track on the week end or just run them hard on a hot summer day. Do yourself a favor. Take your heads to a professional engine builder in good standing, one who is familiar with these engines and there issue’s. Then defer to their judgment. Not everyone attacks this problem in the exact same way.

 

https://www.corvetteforum.com/forum...um.com/forums/c6-corvette-zr1-and-z06/3653716-qustions-for-darrin-morgan-4.html

 

Every LS engine uses powdered metal guides and steel valves. I dont think there is any sense in saying that this is anything other than machining errors in some LS7 heads or its bad coating process on the Ti valves or something like that. Lots go 100k without problem, and some weve replaced at 19k. The engine does know it says Z06 on the fender so Im not sure why the one guy thought LS7 guides cant be fixed in a manner to last so he switched to LS3 heads thats kinda silly. Fix your guides, fix your valvetrain and youve fixed your problem

 

Advanced induction, send them heads have them replace guides and mill heads check valves out. Cheapest easiest solution that I wouldnt be worried about

He should do a cam at same time... but get it from someone that actually knows what they are doing not these parts whorehouses. Ive made a living doing custom cams for these engines for 15 years because most of the "leaders" are great at trashing parts and building terds :/

 

No matter what you do, just be prepared to freshen the heads once and a while. On my street car I will pull them at 20k miles or so and go through them to be safe. Shifting at 7000-7500 all the time on the street/strip and running Ti valves I just don't see it as unreasonable maintenance.



I have seen a lot of these "fixes" for LS7 heads and none last for ever.

 

Think Granny missed that.. Tanner stated he has re done WCCH and others that was Suppose to fix the problem.