LS7 Failures in the Z/28's How Many?

[DasBaldDog]

Originally Posted by hjdca

Is there a reason the intake guides are mostly the ones "out of spec." ? Could it be that they were assembled that way and it was not "wear" that caused the issue ? The exhaust guide specs seem to show zero wear.

The theory I have heard/read is that the intake coating is imperfect/wears/cracks and starts to act like sandpaper on the guide.



*whispers* People keep saying "wear".... no one has proven its wear. They have proven its wrong, but never shown that it was ever "right".

[BJJKRIS]

Originally Posted by DasBaldDog

The theory I have heard/read is that the intake coating is imperfect/wears/cracks and starts to act like sandpaper on the guide.







*whispers* People keep saying "wear".... no one has proven its wear. They have proven its wrong, but never shown that it was ever "right".

That is another theory. Some argue the micro polishing/tumbling procedure corrects that issue. In reality it’s probably more of a perfect storm of design flaws as mentioned above.


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[Gbland60]

Originally Posted by hjdca

Is there a reason the intake guides are mostly the ones "out of spec." ? Could it be that they were assembled that way and it was not "wear" that caused the issue ? The exhaust guide specs seem to show zero wear.

Titanium is some hard stuff and that's the issue I have with running bronze guides on the intakes. Magnesium bronzanium from everything I've read is the way to go if you going to keep your titanium. They're not cheap but I'm going to find out more if it's possible to run a different guide on the exhaust side if one were just going to use a stainless exhaust valve possibly getting away with bronze whatever would dissipate the heat quicker would be the way that I am going to try to go. It's amazing that all of these head shops I haven't even mentioned the fact that titanium is such a course material that the effects it would have on bronze could be just as bad as powdered metal guides that are in there now but I really haven't done a lot of checking yet so I'm just talking off the top of my head please somebody correct me if I'm wrong cuz I sure don't want to go down the wrong road

[BJJKRIS]

Originally Posted by Gbland60

Titanium is some hard stuff and that's the issue I have with running bronze guides on the intakes. Magnesium bronzanium from everything I've read is the way to go if you going to keep your titanium. They're not cheap but I'm going to find out more if it's possible to run a different guide on the exhaust side if one were just going to use a stainless exhaust valve possibly getting away with bronze whatever would dissipate the heat quicker would be the way that I am going to try to go. It's amazing that all of these head shops I haven't even mentioned the fact that titanium is such a course material that the effects it would have on bronze could be just as bad as powdered metal guides that are in there now but I really haven't done a lot of checking yet so I'm just talking off the top of my head please somebody correct me if I'm wrong cuz I sure don't want to go down the wrong road

While titanium alloys are quite hard, they are no harder than the highest grades of steel. But it has exceptional strength to weight ratio which is why it is commonly used in intake valves and even some exhaust valves (Yamaha). Pure titanium isn’t much stronger than even aluminum, it’s not until it’s alloyed with something else do we see it used in applications that were used to seeing. As I understand, because it’s lighter it is more controllable under high rpm’s with a lighter spring allowing it to sustain extended periods without the same wear as a heavier stainless valve. As far is it wearing bronze guides faster than anything else... I wouldn’t suspect that the finish on these titanium valves is any rougher than stainless. Probably the opposite.


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[Gbland60]

Tried to upload the video but wouldn't let me. Something about security token. Maybe its just my old phone. Anyway after checking #1intake i decided whats the point in going any further right. Well, looks like gonna be pulling heads sooner than i thought. And the guy that said if we dont track our cars we should be ok well, we're not. I was gearing up to start next month and now this. I don't beat up on my car and im showing this much wear. I run my Dakota work truck harder than this car. Shitty workmanship for only having 14,307 miles on it .

[1970judge]

Wiggle test is outdated.

https://www.corvetteforum.com/forums...uide-news.html

[Gbland60]

I seen the gap marcus. I didnt have to pull the head to mic the stem and mic the inside guide and do all the math. I cant get video to load up but piston was tdc and valve was closed when i dialed it and it was .018. Opened it about what i thought was .593 in lift and checked and was .020. It doesn't look bad per say and i probably wouldnt worry if it were old cast iron heads with steel valves . Just my paranoia marcus . .0037 ain't a whole lot.020 is a big gap

[Gbland60]

I read hal's article awhile back. I thought then we all would be ok since all ls7's after 2014 it said were built at a different facility or something like that , separating them from the c6 ls7's. Or atleast thats how i interpreted it. Anyway it was an encouraging read for me , at the time. Lol good luck lil buddy .

[DasBaldDog]

Originally Posted by 1970judge

Wiggle test is outdated.

https://www.corvetteforum.com/forums...uide-news.html

Outdated, yes but not wholly without value.

[j o n]

Shop or vendor should do a group buy on head exchange and/or install. Then measure all the heads' valve guides for data. That way it's a consistent and measurable sample size.

[1970judge]

Originally Posted by DasBaldDog

Outdated, yes but not wholly without value.

I disagree, its an inaccurate test. GM agrees so they dropped the test method. Everyones BELOVED KATECH also agrees. Throughout these threads, people claim to have read all of the info, all the articles, all the bulletins, then show up and recommend an outdated test that even their preferred shop has disavowed.

[Russell James]

Originally Posted by Gbland60

I seen the gap marcus. I didnt have to pull the head to mic the stem and mic the inside guide and do all the math. I cant get video to load up but piston was tdc and valve was closed when i dialed it and it was .018. Opened it about what i thought was .593 in lift and checked and was .020. It doesn't look bad per say and i probably wouldnt worry if it were old cast iron heads with steel valves . Just my paranoia marcus . .0037 ain't a whole lot.020 is a big gap

The only way to measure valve stem to guide clearance is disassemble, mic stem and guide in 3 places then do the subtraction.

Having the valve in the head is like asking how much a teeter totter moves... depends where you measure it. That a lot at the ends becomes a little in the middle.

If using a dial indicator at the end of the valve stem in the head, you are measuring something there is no spec for. But... at the same time, really wobbly is really wobbly and as a shade tree look see, it's pretty telling. Won't be able to site a number to say - this measurement was in/out of this spec... just that - it wobbles a lot.

[Zslash28]

Track at your own risk? After some of this new info, confirming a potential for valve guide wear, I am on the fence if I should just let the warranty cover it if it pops, or get the heads done for peace of mind.

[1970judge]

Originally Posted by Zslash28

Track at your own risk? After some of this new info, confirming a potential for valve guide wear, I am on the fence if I should just let the warranty cover it if it pops, or get the heads done for peace of mind.

If you have warranty left, i cant begin to understand the reason why you would preemptively do anything.

A) it pops under warranty, they fix it...under warranty, and you have nothing more than a crummy afternoon waiting on a tow truck.

B) GM decides to say, nah man, you opened your hood that one time, warranty voided, replacement denied. You spend your dime getting new heads.

C) You spend your dime getting new heads, preemptively.

Option B and C cost the same, save for a 100$ tow bill? Option B only costs a little more if you’re trying to slide one by the dealer. Which, you should know going into the deal that, there is a potential they’ll deny me because i installed this or that.

What is option C gaining you? Other than keeping your car off a flat bed, maybe, one day.

If its got warranty, let it ride. IMO of course. Once the warranty is up, sure, maybe i’ll call KATECH and upgrade some things here and there and if business is really good i’ll build an engine to my personal liking. Otherwise, like I mentioned to some buddies recently: i fall into the “im going to shift this mother****er at 7k, if it holds great, if it doesnt, great [on the track, im not a highway jackass]”. Im a realist.