240sx2jz

Good thought...but they are machined (drilled) I have seen the helical cut lines which are created from a drilling process.

Got some more info from my buddy with the 2006 that took a poop. Cruising on the highway 1800 rpms, hears a little sputtering and hesitation. Pulls of the highway, pops the hood and it's still misfiring a little. Decides something is definitely wrong, limps it home. After he pulls the head finds a missing exhaust valve head in cylinder 1 and it's no where to be found haha. It must have made its way out the exhaust somehow which I found to be quite puzzling, it must have been broken into a couple pieces. No tune, bone stock, 20k miles and never tracked.

LS7 BUD

That's wild...

Hirohawa

Is he the original owner?

Apologies if you have posted this before.

krackenvette

Wouldnt it suck if the Pace car dropped a valve today at Indy........

scottmotox

thanks for the reply dirty howie. i was looking to make it sound a little meaner lol. i may eventually do a tune but not till its out of warranty. will the headers and exhaust change the sound a lot or is not worth putting that much money into it? i could always swap back to the stock exhaust before i took it to the dealer but knowing my luck something would happen when i was out of state with it and then id be screwed.
so do some of the aftermarket guys do some improvements to the valve train that makes them not wear? for example, Lingenfelter has that heads and cam package(and other stuff) and they offer a 3/36,000 mile warranty. if a cam wears out the valve train that quickly wouldn't Lingenfelter be doing a lot of warranty work? just asking cause i dont know.

scottmotox

i can of ran my comments and questions together on my last post so heres my question.

so do some of the aftermarket guys do some improvements to the valve train that makes them not wear? for example, Lingenfelter has that heads and cam package(and other stuff) and they offer a 3/36,000 mile warranty. if a cam wears out the valve train that quickly wouldn't Lingenfelter be doing a lot of warranty work? just asking cause i dont know.

valet_devil

[QUOTE=240sx2jz

I was thinking about tossing a valve in a tempering oven we have and cranking it up to 1500F and letting it hang out for a couple hours to see if anything started to show any signs of failure. But I'm a little leerie as to what will happen if the thing comes apart. I would characterize the valve before throwing it in just to have some baseline dimensional info before the heating cycle. Anyone think this is a waste of time?? Or something worth investigating??[/QUOTE]

Showed this to my published materials engineer friend and she said if you're trying to fatigue it for noticeable signs of wear you're going to have to send it through many heat cycles, fully hot then cold for many times. Looking at a chart of high-temp steels (aviation engines) some don't show any signs of wear until 100 such extreme cycles. Thanks again for your work.

240sx2jz

Thanks for the response, I wasn't really thinking fatigue (she is 100% correct). more if there is a reaction that could occur from the amount of sodium in the stainless at that temperature. I don't know if the sodium has a key temperature or time where it becomes really volitile and could effect the stainless. Maybe you could ask her about that??

valet_devil

To do that she really needs to know exactly what kind of steel is used. She searched ls7 exhaust valve composition on google for thirty minutes. Cool girl, huh?

hoefi

Yes, service limit is 0.0037". Beyond that, exhaust valve stem will start to have problem getting rid of excess heat if the engine is driven really hard with long duration WOT. By the time clearance gets to around .007", galling will start to take place (as per evidence from my engine tear down inspection). From this point on, the valve stem is like a file and guide wear is really accelerated. My failed valve's corresponding guide clearance was 0.016". No valve will survive that type of clearance in my opionion. #1 exhaust is the broken valve.



Basically, there are three stages which leads up to a dropped valve scenario:

Stage 1 - factory clearance which somehow has abnormal high guide wear. Mine wore to the factory service limit (~.004") within 11,000 miles. Of that, there was only about 80 track miles. Six out of the eight exhaust guides are all sitting at this service limit. Stock engine, multiple oil changes during that period.

Stage 2 - Guide clearance between .004" to 0.007". If guide wear is dectected during this stage, it's only a matter in changing them out. I think so far, most of the excessive guide wear (with no dropped valve) are dectected druing this stage. During this stage, if the owner does not drive his car hard, the valve stem will most likely remain smooth and this stage could last long as the vehicle continues to gain mileage.

Stage 3 - Guide clearance between .007 to .015+". During this stage, any type of hard driving could easily induce material transfer on the valve stem. Once that takes place, stem becomes rough and galled. Accelerated wear will then take place regardless of how easy the owner drives his car afterwards. This stage won't last that long and once the guide clearance gets up to double digit thous, the valve head will eventually falls off.

Stage 2 and 3 are merely the end result of stage 1. The most troubled part is still understanding why stage 1 can happen so fast for some of the cars. For my own car, it could be due to excessive cold oil. Up until my valve dropped, most of the 11,000 miles I logged were short duration trips. The car was insured all year round and a lot of trips during the winter months were done in near freezing temperature (I am in Canada). I remember the oil would take easily 20 minutes to struggle up to 120 degrees. A lot of the trips were only 10 to 15 minutes long and the oil temp never went pass 100. I remember even a lot of the longer trips on the freeway, the oil never went pass 140 degrees. The high mileage LS7s we see on this board no doubt did not logged those miles doing 10 minute short trips. Having the car in warmer southern states don't hurt either. Storing the car for the winter also eliminates the cold short trips. The later ('09+ model) liquid/liquid oil cooler might be GM's way of correcting this issue. They might have reconized a potential problem there.

The trick to prevent a dropped valve is to try to catch the guide clearance during stage 2. Especially for owners who do a lot of short trips in cold regions and then would take their cars to the tracks during the weekends in the summer.

hoefi

Not really. A tight radius curved surface like a valve stem is very resistance to small surface buckling. Also, measurements of my own valve stems (even with noticable heat discoloration) were spot on, in all direction, all the way up the stem.

hoefi

Yes, I agree. All along, I have been saying that. Once the guide clearance excess 0.004", it will only get worse. Machines, unlike the human body, do not heal themselves. Once it gets into what I called Stage 2, it's only a matter of time that the valve will drop, good valve or not. Driving the car really hard will accelerate this. Having a bad valve (with internal machine marks and thin wall) will accelerate this also.

I have reiterated this along with a lot of other posts on the subject during the last three years since my engine blew in September 2009. I believe I am the first person reported the exhaust guide wear on this forum (back in January 2010). At the time, I mentioned bronze guide as a possible solution, roller tick rocker was another, coating the valve head with a thermo barrier coating was another. I explained the reason why GM ran such a rich air fuel ratio inorder to contain combustion heat (which AirbusPilot didn't like). I have been accused of missing shift to running the engine down on oil. As the saying goes, been there done that.

I have posted, I believe, a lot of good info on the subject. Most of them are here:
http://forums.corvetteforum.com/c6-z...valve-and.html

Yes, there are 23 pages, hope you have the time while writting all those other replies in the other threads.

vertC6

Agree 100%, we are definitely on the same page

hoefi

The quantity of heat is not affected by the wall thickness of the stem. When the stem clearance is tight, lots of heat will transfer to the guide, thus keeping the valve stem temperature down.[/QUOTE]

Not necessarily, depending on the time the valve spends in the stream of exhaust and the specific heat of the material and the mass of the region you will end up with spots which will heat more quickly. This could definitely "shock" the material and induce stress and fatigue.

I was thinking about tossing a valve in a tempering oven we have and cranking it up to 1500F and letting it hang out for a couple hours to see if anything started to show any signs of failure. But I'm a little leerie as to what will happen if the thing comes apart. I would characterize the valve before throwing it in just to have some baseline dimensional info before the heating cycle. Anyone think this is a waste of time?? Or something worth investigating??[/QUOTE]

Understood regarding your desire to examine the weld. Finding the machine marks (bad) and the cavity eccentricity certainly confirmed one of my earlier concern also. Back in September 2009, I wrote a letter to GM when my engine blew, and I questioned GM's outside engineer's report. Two of my questions were the valve stem wall thickness and cavity concentricity. See middle of the page in the photo below.





In regarding to your oven test, I think it won't show much. 1500 degrees is nothing for the valve. It can see that all day long. Even in a failed valve, the basic valve itself is still in pretty good shape, except with the head broken off. I had one valve cleaned up with walnut shell blasting. This valve came out from a guide which had a 0.008" clearance. It had all the symptoms with overheating; minor material transfer on the stem, discoloration etcs. The dimensions were spot on, dectected no crack. It looked new after it got cleaned up. The problem is in the worn guide. Once it gets too loose, the head will eventually break off. Having machine marks inside certainly don't help. They should be honed after drilling in my opinion.

H82BFST

Corvette forum soap opera...

So, can someone provide a short timeline? So many threads jumping around everywhere and I can't seem to seperate the plays (LS7bud, z0sicktanner, chad...). Same guys differnet guys. At one point I could have sworn z0sicktanner was a full time head porter but then I ran into this thread and was wondering why he didn't just port his own heads? http://forums.corvetteforum.com/1578952098-post13.html But then it made me wonder what car of his blew up of his that started his rage about the heads and if it was the same one as for some reason I thought his was stock being replaced under warranty.

I've been reading these type of LS engine based soap operas on LS based forums since 1990 but I have to admit, this one has so many thread and players that die and come back that it's almost impossible to keep up. In the end, I'd like to know what shop z0sicktanner (err chad) ports for since he does this for a living and did he infact run his own heads or another shops, and what blew up?

LS7 BUD

Two different guys... My name is Damien... I'm sure chad will tell you why he did what he did... I know why but it's up to him to tell you...

AzDave47

That change was MY 2011. My 09 has the air/oil cooler and I was corrected when I said 2010 was the change year. I'm in the AZ high desert (5400') and see most of my short drives with oil temp <150*.

When I ran M1 5W-30 I would back off at HPDE's at 260* oil temp. Now I'm running M1 0W-40. The 2 Blackstone Lab analyses of my M1 5W-30 after 5000 miles and 4600 miles were good and still had TBN's of 9.7 and 5.8.

The low TBN sample included 6 passes at the Mojave Magnum (standing start 1 1/2 mile trap speed event) where the engine spent ~ 35 seconds each pass at high RPM including most of it at full throttle. Nearly 1 mile of that was full throttle in 5th gear from a 160+MPH 7K RPM shift from 4th. Oil temp at the start of each pass was ~ 160* and about 200* at the end of each pass. Water temp at 190-200*.

Hirohawa

This didn't last long at all.

Fly'n Family

Wow.......that sucks.

SRVfan09

I would be willing to bet it is 440C as it is high in carbon content and is stronger than other stainless steels (i.e. 316, 304 etc.)