Michael_D

I'm not sure if I'd say that. There are several points to consider, like condition of guides/seats/valves/springs/spring retainers/stem locks/seals/etc.

Too-Fast

Thanks for posting, great information.

Michael_D

Thanks. And thanks to everyone else for the nice comments.

I may add pictures later.

I had also thought to put something together that would discuss guide type/alloys/manufacturing/ect in the second post. Brain storming that idea now, as I want to keep my personal opinions out of the discussion.

The hour glass wear pattern is created by where the binding occurs; the tip of the stem, or the valve head. If the rocker pushes the stem, then you will see more wear on the top of the guide. If the valve head lands on a seat that is not concentric to the guide, the valve head will be pushed directionally, causing the stem to rub/bind at the bottom of the guide.

HOXXOH

Of course, the first question to be asked would be if the order presented matches the order of the highest likelyhood during failure analysis. Since causes 3 thru 7 could be more tightly controlled during the manufacturing process to avoid failure, you would logically think GM would have addressed the areas where they had the capability to do so. Causes 1 and 2 are outside the control of GM for the most part, which would tend to question how owners use the car rather than the products they use in the car. It's well established that dry sump lubrication is advantageous for track use, but there's not a lot of data regarding street usage. This forum has the best opportunity to collect that data.

Vito.A

Very good list. Obviously lots of thought went into this. I suspect our Mobil 1 oil from when the testing was done (aprox 2005) has changed quite a lot.


Another point of concern is IF the seats are not concentric with the guide, then some of us should have had excessive leakdown around the valves when the cars were new. As the guide wears, then the valve will tend to center itself on the seat. I have not seen anyone with excessive leakdown on a new LS7. This pushes me to believe there is excessive side loading from the rockers combined with poor oiling and poor metallurgy.

Michael_D

You can have run out in excess of five thou, and with just light pressure on the valve with your finger, it will seat well enough to hold liquid (the contact area of the valve and seat isn't much on four/five angle valve jobs). Having said that, I would not conclude that a satisfactory leak down test, with spring load, would tell you if the seat/guide concentricity is within tolerances.

Bad_AX

So please tell us what mistake(s) the engineers made in the design. If you "don't care who makes the mistake", I hope you never get called for jury duty. All the factors that Michael researched and presented have much to do the production process and quality controls, and not so much with the design.

RamAir972003

I did all those things hopefully when I pull them soon they will be ok we still don't have a 100% fix to this issue, but we are getting closer...god bless us...

AimHigh

Yep, but GM darn sure won't fix my car if it blows……still.

Vito.A

GM really couldn't care less about these cars/engines. All the engineering and development was done over 10 years ago.

Sébast19X

Great information, thx to post.

Seb

MTIRC6Z

You may not care but anyone who wishes to rectify the problem as intelligently as possible sure cares.

You see IF one understands that the engineering is not at fault, it removes a significant number of variables as to what the real cause is and saves you from trying to reengineer to get an appropriate fix. Simply having to ensure execution is good is a far easier than having to chase after an engineering problem.

Your post demonstrates a degree of emotion which will never help in trying to find an appropriate solution and often leads to making mistakes when executing a 'fix'.

My hat is off to the OP, excellent information that is clearly worthy of being a sticky.

Cheers, Paul.

GOLD72

I have suspected for a very long time that a lack of adequate quality control and inspection from GM with the supplier of these heads with valve trains has resulted in so many defective heads installed on LS7s.

AZDANZ06

A reasonable person would tend to believe they would inspect every component since these engines are "Hand Built"

383

I suspect they're organic robots.

AZDANZ06

Mr. Jean

Yup, what he said. Thanks.

Vette @ 71

With the vast amount of available measured data on guide wear coupled with the design of the valve train/ clearances/ lubrication etc. do you believe it's possible, to a fair degree of certainty, to assess the most likely candidate(s) responsible for the guide wear. If so, what would be your most likely opinion.

Thanks for all your support here..

juanvaldez

Impossible to check every dimension even on hand built engine. The guys that assemble the LS7 motors likely don't check anything. If you are doing two motors a day you don't have time.

MTIRC6Z

Not that you asked me, BUT...I'd say #4 and #6, with the really unlucky guys getting both issues on one set of heads and not finding about #6 until after they fixed #4 only to find their guides to be out of spec a second time

I guess it would be just as bad to have only issue #6 and do a fix which would solve issue #4 (one that you didn't have)...because without fixing #6 your worn guides would return.

So what it really comes down to is, if you have improperly located rocker pedestals (ie. issue #6) life sucks a lot worse than if you had only issue #4 (ie. the concentricity problem).

Cheers, Paul.