Mark2009

ConfusedGarage

Quick, did you find the link to the thread with Z06_505's failure? Didn't we all read that recently and determine there were no guide measurements to show they were in spec? I thought I recalled seeing the quote, "some wear" as the description in that thread, but nothing definitive. I could be wrong, which is why I'm asking, no tone intended if it comes across that way.

I don't really care about anything else right now except finding if any valves have failed with guides in spec, and I guess this is the one data point to look at now.

'06 Quicksilver Z06

Yes, see post #38.

I again point out that I find it curious that Mark200X points to Chad's video of a 2010 which dropped a valve and shows excessive guide wear.

But dismissed the Z06_505 dropped valve case where there was no excessive play in the guides.

But aside from the Z06_505 case, what other cases can we find where there were actual guide measurements to show they were in, or out of, spec?

I wish you the best in that endeavor. But until it becomes a matter of routine, or near a matter of routine, we do not, and will not have such information, and it is indeed crucial information in this matter.

However when I take into account variations of wall thickness discovered by a forum member here, variations in sodium quantity found inside the stock valves by another, milling marks inside the stock hollow valve stems, I am not ready to dismiss the prospect that the valves themselves might be a major player in these valve failures, merely on the "strength" of us not finding any "exhaust valve failures inside of in spec guides", which we seldom if ever look for to determine anyway.

In a nutshelll, some believe that it is the valves, the guides and the rockers, and change all three. WhiteDiamond, tjwong.

Some believe that it is potentially the guides and the valves and so change both. Several others in here have done so.

Some believe that it just the guides and the other's the valves and the rockers are not a potential issue, and so change the guides only.

The option to do whatever, is the car owner's based on a gathering of the available facts, weighing said facts, and an honest assessment of which facts would be beneficial, but are as yet unavailable.

Random84

The guide tolerances were NOT checked at Wixom by the engine assemblers (please correct me if I'm mistaken here), and I doubt they were even after inconsistencies were admitted by GM.

You are right, there is a production tolerance, but to my knowledge the subcontractor was in charge of actually verifying that tolerance (because the heads arrive at wixom fully assembled). Just as GM announced there were machining errors in later year heads, these errors were also based on "tolerances" that were simply missed by the subcontractor and that which GM assumed were accurate (until physical inspections proved otherwise).

So, realistically, it doesn't matter what the spec is - people still assume that 240,000+ sintered guides are all going to be within spec, or that the subcontractor is checking each and every one (and the diameter of the exhaust valve that goes into it) to ensure uniformity. I think we all know that, realistically, that each part will have variation and only random checks are being done to ensure consistency. Based on these samplings, "specification" is being extrapolated to entire lots of product to meet the desired result: guide tolerance that should be within 0.001 to 0.0025".

Unfortunately, every manufacturer slips out a lemon or three - so that's why one of my big issues with some who assumue the valve itself is the sole culprit: we have to assume each and every guide is made "to spec" before that logic can be believed (a loose guide tolerance = oil coking = poor heat transfer and increased wear/fatigue = snapped valves).

Having one or two late-model Z's show up with out-of-spec guides with no more than a few hundred miles on the odometer (combined with the successes of aftermarket shops using OEM valves) leads me to believe this idea may be distorting what we think we know. Food for thought.

Vette @ 71

When in doubt or in those circumstances when conflicting opinion is offered, one should seek out an expert on the subject...If the person can provide actual evidence of and proof of solution, then this is the guy I will accept until proven otherwise..

The expert I called upon was Katech...No additional info needs to be provided as to their qualifications on the LS7 or this subject..Katech say's the problem with the LS7 valve drop is the OEM guides..Their recommendation was to replace them with Bronze and OEM ex valves along with a change to the intake valve for compatibility to the bronze..

spicytuna

But they also said this :
http://ls1tech.com/forums/17205783-post64.html

ConfusedGarage

I didn't see guide spec measurements anywhere in there. Are they available? I'd really like to look at each guide spec and compare it to the one that failed, and then compare it to our own measurements in the spec thread.

I see chad's offer to mail one of us the head, but then I would just have to mail it to WCCH, what a hassle. From what you are saying there are measurements available and they show the guides within the service limit per GM correct? I just want to be clear as people tend to mud up their posts and most don't care to sift through the banter. Nobody is calling anyone out here, just clarifying as this would be a critical piece of data and the very first proven case of in spec guide/failed valve.

'06 Quicksilver Z06

What I'm saying is that this was the report from two forum members who are familiar with Z06_505's case.

If you would like more specifics and are more curious as to how they arrived at their assessments, then I strongly encourage you to contact both forum members with regard to that as your best option for getting a first hand account of just how they made their determination.

As they are the ones who would have performed any measurements, they, better than I, would be able to tell you what they measured with.

And I can respect that.

Why don't you contact Chad, Z06_505, and 240sx2jz if you would like more specifics and wish not to "sift through the banter"?

In the meantime though, I would like to repeat my request that you post up 5 cases of exhaust valve failure in here where the guides were shown to have been out of spec, following the failures, using the same measurement techniques which you are calling for in the Z06_505 case.

fnunez

Found this link on youtube, guy seems to know what he is doing/talking about. I own a 2008 Z06 with a new 2011 engine replaced by dealership under factory warranty because of the valve guide issue. This new engine only has 800 miles on it, I will remove the heads ASAP and repair all that is wrong with them or not wrong with them, so that I may feel safer when racing, good luck.

Dirty Howie

You can search my threads. My '08 lost motor most likely to valve guide wear and broken valve head. My replacement '11 motor had excessive guide wear after about 30k miles. Now I have rebuilt stock heads by WCCH

My car was and is stock but I do track it once a month.


DH

Bill Dearborn

I don't think you can assume any stock engine is not going to drop a valve. My completely stock 08 LS7 engine dropped the exhaust valve in #1 cylinder at ~ 24K miles. Engine was stock right down to having the original air filter. It had 40 track days (not drag racing, hard track miles) on it. My replacement engine was built in May 2011 and I don't know whether there is an issue with it or not.

Bill

ZeeOSix

His conclusion of "that's insane" pertaining to the exhaust valve guide wear is correct ... it is insane.

It's the same BS GM pulled with the failing valve spring issues on the LS6 ... they did nothing special for a major screw up except to fix it if something failed under warranty.

spicytuna

I'm sure z0sicktanner (who's a regular on this forum) will appreciate those words.

z0sicktanner

I had z06-505's heads...valves were all in spec. I have the specs at home.. but from what i remember the worst valve was .0019 top .0016 mid .0021 bot...if im wrong I will change when I get home...

z0sicktanner

z0sicktanner

Nice find...

z0sicktanner

Hey NO prob.....but this head in the vid was out of spec bad.... .0100 plus on 2 exhaust valves

2k Cobra

Mine is a "100% Stock" 07, No mods, 43 K miles and heads were junk.
Properly maintained, never tracked.

ZIE06Bernie

Well the video is sure a shocker with guide slop like the vid shows - no wonder the valves break.

However what I cannot fathom is this. Why is the problem only affecting the exhaust valves as shown in the video with good tolerances on the intakes wiggle test. Seems difficult to believe the exhaust valves would be the only ones to have been fitted with out of tolerance guides.

I read someone talking about concentricity of guide and valve but surely that couldn't be the cause otherwise it would have shown up either visually or with misfiring due to bad seating caused by the mismatch seat to valve face. That just makes no sense to me.

Any answers I have missed that could sanely explain why this is only exhaust valves?

'06 Quicksilver Z06

Please let us know what you find here Chad.

Thanks.