Help! Valve guide wear on ZO6 427 engine

[TheBugster]

I have a 2007 ZO6 with 40000 mi. on it. I haven't experienced any obvious issue with the engine at this point; however, a local Corvette shop has recommended that I have the heads removed and examined to prevent the possibility of major damage to the engine.

Is this a good idea? Does anyone know how widespread this problem is? Is there any recourse with GM?

Any recommendations or information would be appreciated.

TheBugster

 

[TooFast]

All LS7 motors are suspect in regard to the valve guide issue due to potential machining errors from Chevys sub that supplied the heads. The only way to tell you have a problem is to either remove the heads and measure the guides or perform a head in place "wiggle test" to determine if there is a problem. If you read Hib Halverson extensive writing on the LS7 he has a pretty good amount of info on the subject. There are a few good head remanufacturing companies that you can also check out. If you want to read until you cannot read anymore on this subject go the Corvette Forum and there are multiple threads about this.

 

[Tuna]

Last I heard, if your haven't experienced any valve guide issues by 15,000 miles, you're probably not going to.

I've got 40K on my 427 and it's still going strong.

 

[TooFast]

Last I heard, if your haven't experienced any valve guide issues by 15,000 miles, you're probably not going to.

I've got 40K on my 427 and it's still going strong.

Tuna, with all due respect and deference, your experience would not preclude your LS7 from the problem. I would recommend you "wiggle" your valves, especially the exhaust side. 15K miles is no marker for the problem, it has been identified by many after 15K miles.

 

[Hib Halverson]

Tuna's engine was built after GM solved the problem.

 

[Tuna]

TooFast: I'm going to leave my engine alone. I don't like doing unnecessary work.

Hib: When did GM "fix" the 427 valve problem?

 

[kpic]

Toofast:
I'm a former mechanical design type, a GD&T (ANSI Y.14.5-2009 and ISO 1101) guru and stack up analysis type. As my last two prior employers were "global," I was required to be bilingual and "spoke" both ANSI and ISO. Personally I dislike ISO as it has too many "books" and [FONT=&quot]ANSI Y.14.5-2009 is one book.
[/FONT]
Stack ups are nothing but a bunch of numbers to say what fits and what doesn't. It goes a lot deeper than my short statement implies.

AFA, the wiggle test. Consider of two sheets of plastic about .045" thick and separated by 4" and sized exactly .001" larger than a perfectly sized dowel. The dowel is .3761 to .3759 (http://www.engineersedge.com/hardware/machine_dowel_pins_chart_ansi_asme__13076.htm)

Insert the dowel and will it wiggle? I don't think so and the space between the plastic sheets in 4". For a "3/8"" dowel to respond appropriately to a wiggle test the guides would be really shot. GM owes their customers a lot better than a wiggle test. Which will only respond appropriately to certain conditions of detrimental wear, but not all wear. The very, very short form is Corvette owners deserve better than quick and dirty.

If you disagree, try the math and you'll discover the angularity between the sheets of plastic is very small when the two lines of contact are separated by 4". The less the separation, the less the wiggle. As two circles only have a single line of contact, the wiggle test documents a lot more wear than I'd want in my engine and ignores a lot more wear than we'd appreciate..
I'm retired or I'd do the math..

 

[LLC5]

Insert the dowel and will it wiggle? I don't think so and the space between the plastic sheets in 4". For a "3/8"" dowel to respond appropriately to a wiggle test the guides would be really shot. GM owes their customers a lot better than a wiggle test. Which will only respond appropriately to certain conditions of detrimental wear, but not all wear. The very, very short form is Corvette owners deserve better than quick and dirty.

That is one of the reasons GM never validated a "wiggle" test for warranty claims. To determine if a valve guide is worn, the head needs to be disassembled and the valve guide and valve stem measured properly, anything else is just a guess.

 

[kpic]

That is one of the reasons GM never validated a "wiggle" test for warranty claims. To determine if a valve guide is worn, the head needs to be disassembled and the valve guide and valve stem measured properly, anything else is just a guess.

As a former "numbers" type. I can't say I blame GM. Simply said, it is another internet legend that doesn't work reliably. Reliable means 100% of the time. As my simple example showed, at best, the wiggle test is inaccurate unless the whole valve guide is worn. A simple measurement with a set of ID ball mikes, says nope..

Measuring properly at the high extremes of accuracy, isn't easy and it is very expensive.. With a valve stem and a guide. At least a Zeiss Contura or Accura.
As a Master Tech, you might enjoy watching this: CONTURA G2 CMM - YouTube

It's called metrology and they can measure easily to a whole bunch of zeros to the right of the decimal in millimeter..

 

[LLC5]

As a former "numbers" type. I can't say I blame GM. Simply said, it is another internet legend that doesn't work reliably. Reliable means 100% of the time. As my simple example showed, at best, the wiggle test is inaccurate unless the whole valve guide is worn. A simple measurement with a set of ID ball mikes, says nope..

Measuring properly at the high extremes of accuracy, isn't easy and it is very expensive.. With a valve stem and a guide. At least a Zeiss Contura or Accura.
As a Master Tech, you might enjoy watching this: CONTURA G2 CMM - YouTube

It's called metrology and they can measure easily to a whole bunch of zeros to the right of the decimal in millimeter..

Good video. When repeatability and accuracy are of primary importance, machines are it.

"Hand built" just doesn't have the same effect (or result) it once had, in fact it's just the opposite now.

 

[kpic]

Good video. When repeatability and accuracy are of primary importance, machines are it.

"Hand built" just doesn't have the same effect (or result) it once had, in fact it's just the opposite now.

Today's machines are something special.

When I got into the business, a dowel's position could be held to less than .012" at a distance of 12" from a center. Position also includes perpendicularity to the mounting surface and rotation or clocking so the mounting holes or threads would align. Today, under .004" is easy. The ease depends on the machine.
The dowel's perpendicularity at its installed height can be controlled with a projected tolerance zone.

Your second sentence is "spot on." In the past, balancing turbocharger or supercharger rotors was done by hand, today is quite a different story:
► CIMAT Supercharger Balancer with Automatic Drilling (Burke Porter Group) - YouTube

The balancing is "boringly" accurate, day in, day out and it even vacuums the chips. In the past, chips were removed using high pressure air.

Assembly is by robots which decrease errors.

 

[Iroc2Vette]

So far, I've had no issues with the valve guide wear. I'm quickly closing in on 55Kmi with 4 1/2 years on this car. I also have about 5 hours of track time on it, too. Not hard track. All instructive where I rarely got out of 4rth gear. I've had 2 oil reports, one through Marathon and the last through Blackstone Labs (28Kmi and 45Kmi respectively). The results were extremely good. Blackstone wrote me back stating my engine was wearing less than a 4 cyl Honda with a 2K-3K oil change. I routinely put over 8Kmi on the oil. I do use a very expensive high film strength ester based synthetic oil. My PT warranty is going bye-bye after October 4rth. Then I'll be on my own. I'm not too worried. The engine is also consuming almost no oil, either. It does tick a bit loudly, but, I understand these LS7 engines are a bit more 'talkative' than the other engines. Otherwise, it still walks or runs away from just about anything out there..Sometimes, I don't even have to downshift. Just plant the gas pedal and go WOT

 

[L over D]

and you just keep driving along....??

Iroc2Vette....sez....
I understand these LS7 engines are a bit more 'talkative' than the other engines.

I like that bit from Iroc.........got to remember it.

Really tho, with all the problematic LS7 motors, one should be proactive ....(unless the car in question is still under warantee).

IF you have a noise in the rocker boxes, without taking much of the upper end apart, a leak down test might give you JUST a sense. However, IF there is ANY adverse noises, pull the rocker covers and look at or remove the rockers and look for missing trunion needles or distorted trunions. Then look at valve tips and lash caps for angularity on the tops. Only IF you have a LOT of valve guide slop can you feel some or none of slop. There is no way (as it was said above) you can "wiggle" to see a dimension of the guide /valve stem. The valves must be removed and guides measured, and heads off of course. By that time you just might replace with decent guides.....I'll stop here. But there is more !! Concentricity, detail and the right parts have to be used......ALTERNATIVELY you can consult your favorite Chevy Dealer :L or go to Canada and complain?

 

[TooFast]

TooFast: I'm going to leave my engine alone. I don't like doing unnecessary work.

Hib: When did GM "fix" the 427 valve problem?

Tuna, with all due respect, Hib's statement caught me off guard a little bit, I am not sure how one could make a statement that a car was built outside the problem range and the issue has been "fixed". The issue appears to have been poor machining by the supplier Linmar and there has not ever been any proof that I have read, that GM addressed that issue...there still have been failures outside the range they claim to have increased their inspection process. I don't want to re-litigate the VG issue here, my 2011 just hit over 3,000 miles, has a good Blacckstone report, but I will be checking my guides this winter. To each his own, no argument from me on your decided course.

 

[Toms007]

Iroc2Vette....sez....
I understand these LS7 engines are a bit more 'talkative' than the other engines.

I like that bit from Iroc.........got to remember it.

Really tho, with all the problematic LS7 motors, one should be proactive ....(unless the car in question is still under warantee).

IF you have a noise in the rocker boxes, without taking much of the upper end apart, a leak down test might give you JUST a sense. However, IF there is ANY adverse noises, pull the rocker covers and look at or remove the rockers and look for missing trunion needles or distorted trunions. Then look at valve tips and lash caps for angularity on the tops. Only IF you have a LOT of valve guide slop can you feel some or none of slop. There is no way (as it was said above) you can "wiggle" to see a dimension of the guide /valve stem. The valves must be removed and guides measured, and heads off of course. By that time you just might replace with decent guides.....I'll stop here. But there is more !! Concentricity, detail and the right parts have to be used......ALTERNATIVELY you can consult your favorite Chevy Dealer :L or go to Canada and complain?

L, I see this is your firs
t post, so "Welcome" to CAC. From the sound of your post, you have some knowledge in the area of engine build/function. We can always use such knowledge here. Don't be shy about posting and enjoy CAC.

 

[Iroc2Vette]

Iroc2Vette....sez....
I understand these LS7 engines are a bit more 'talkative' than the other engines.

I like that bit from Iroc.........got to remember it.

Really tho, with all the problematic LS7 motors, one should be proactive ....(unless the car in question is still under warantee).

IF you have a noise in the rocker boxes, without taking much of the upper end apart, a leak down test might give you JUST a sense. However, IF there is ANY adverse noises, pull the rocker covers and look at or remove the rockers and look for missing trunion needles or distorted trunions. Then look at valve tips and lash caps for angularity on the tops. Only IF you have a LOT of valve guide slop can you feel some or none of slop. There is no way (as it was said above) you can "wiggle" to see a dimension of the guide /valve stem. The valves must be removed and guides measured, and heads off of course. By that time you just might replace with decent guides.....I'll stop here. But there is more !! Concentricity, detail and the right parts have to be used......ALTERNATIVELY you can consult your favorite Chevy Dealer :L or go to Canada and complain?

I saw a youtube video of what that level of rocker arm and high valve train noise is. The engine sounds like it's a damn bloody diesel at idle. It's incredibly loud. My engine just makes a light 'ticking' noise. Rev the engine a bit and it gets buried within the exhaust and intake noise. In my view, this is perfectly normal.

However, if I were to buy one of these cars used that are in the 2008-early 2011 range, I'd def. have the heads removed and do a full 3D micro scan analysis. And plan that into the purchase cost of the car. Last I saw, a crate long block is about $17K US. Plus probably another $3K to swap out?

From what I understand, the bottom line on the machining is that the center point of the valve stem tip doesn't perfectly aline with the center tip of the rocker roller. Thereby creating side to side thrust loads against the valve stem and guide wall. Causing excessive wear. This is the only way I can figure out what's going on that makes any sense to me. And I figure if I've gone 55K, including 5 hours of track time, I should be in the clear...I'm hoping...I plan on putting over 200Kmi on this car and still having it look and run almost show room...I even swapped out all 7 fluid related systems 10Kmi ago...

 

[Hib Halverson]

If an LS7 is in good condition, it does not sound like a "bloody diesel". LS7 valve train noise is only slightly more noticeable than that from an LS3 or LS9.

Basing one's understanding of LS7 valve train noise on YouTube clips is a fool's errand because you have no idea of where the microphone was located during the recording.

Neither GM nor a source outside of GM with any credibility has cited breakpoints for heads with problematic guides. It's generally accepted that engines from mid-'07 to late-'12 MAY have problems with prematurely worn guides.

The problem is not caused by anything related to rocker arms. It is caused by lack of concentricity between the centerline of the valve seat and the CL of the guide. That causes a high level of guide wear.

During LS7 head production, the supplier, Linamar, may have had one of its several CNC machines improperly set-up or in faulty condition. Additionally, there was no QC of finished guides and seats. The result was some, but not all, LS7 heads had guides and seats which were not concentric. As a result, not every LS7 engine has problems with guide wear.

Generally, engines with less than 5000 miles on them, even if the guides and seats are not concentric, will not show symptoms of the problem.

In most cases, a check for guide wear usually requires removal and disassembly of the heads. The valve stems are mic'ed and the guides are measured with either a hole gauge or a micrometer bore gauge.

There is much discussion on forums of the so-called "Wiggle Test". In most cases the wiggle testing is grossly inaccurate. The exception is if the test is done very carefully according to the instructions in an article which is elsewhere on the CAC, but even done that way, the Wiggle Test is really problematic is when the amount of guide wear is only a little more or a little less than GM's Service Maximum.

The solution to the problem is to replace the guides with aftermarket guides from CHE Precision and finish them such that valve runout is no more than .0005

 

[Iroc2Vette]

If an LS7 is in good condition, it does not sound like a "bloody diesel". LS7 valve train noise is only slightly more noticeable than that from an LS3 or LS9.

Basing one's understanding of LS7 valve train noise on YouTube clips is a fool's errand because you have no idea of where the microphone was located during the recording.

Neither GM nor a source outside of GM with any credibility has cited breakpoints for heads with problematic guides. It's generally accepted that engines from mid-'07 to late-'12 MAY have problems with prematurely worn guides.

The problem is not caused by anything related to rocker arms. It is caused by lack of concentricity between the centerline of the valve seat and the CL of the guide. That causes a high level of guide wear.

During LS7 head production, the supplier, Linamar, may have had one of its several CNC machines improperly set-up or in faulty condition. Additionally, there was no QC of finished guides and seats. The result was some, but not all, LS7 heads had guides and seats which were not concentric. As a result, not every LS7 engine has problems with guide wear.

Generally, engines with less than 5000 miles on them, even if the guides and seats are not concentric, will not show symptoms of the problem.

In most cases, a check for guide wear usually requires removal and disassembly of the heads. The valve stems are mic'ed and the guides are measured with either a hole gauge or a micrometer bore gauge.

There is much discussion on forums of the so-called "Wiggle Test". In most cases the wiggle testing is grossly inaccurate. The exception is if the test is done very carefully according to the instructions in an article which is elsewhere on the CAC, but even done that way, the Wiggle Test is really problematic is when the amount of guide wear is only a little more or a little less than GM's Service Maximum.

The solution to the problem is to replace the guides with aftermarket guides from CHE Precision and finish them such that valve runout is no more than .0005

That's very true. Microphone placement can definitely accentuate certain sounds more than others. I used to do a lot of recording back in my days. But, in this case, it seemed like the engine in this video had the rocker trunnion needle bearing issue. But, the clacking was super loud. I'm probably wrong then.

And thanks for being very specific with the information on this issue. I obviously had certain misconceptions and inaccuracies in my statements. I stand corrected. It'd due to my misunderstanding of certain points on this issue. Like I remember seeing in your article that as of February 2011, GM asked Linmar(sp?) to do a 100% inspection. Some say this is kind of like letting the fox guard the hen house. Or, there were heads left in inventory from before that time, which might've been used in the later 2012 engines? Since you're essentially in the trenches about this issue, you'll know more than anyone outside of the engineers involved who you interviewed.

One thing I'm always afraid of is trying to find someone locally who's competent and honest enough to remove the heads and do a complete inspection and necessary repairs. I've heard some unscrupulous machine shops profit by the customer's fears even though the heads may be fine. If I remember reading correctly, GM was also concerned about this being the case. Heads being serviced which had no need of it.

So though my PT warranty is up next month, I'll continue to solder on with the hopes nothing will happen. Since you mention the problem ends mid 2012, then perhaps I dodged a bullet and don't have to worry about it. I'd like to keep the car. I really do like it a lot. I can't think of anything else for the $ which has all it's attributes.

 

[Hib Halverson]

If the engine in the YouTube clip had the needle bearing problem, which, of course, is completely different from the guide wear issue, and was covered under the GM campaign, then it would make a lot of valve noise but, only from the rocker(s) which had failed bearings. Some of the owners of the cars which had bad rockers, had kittens when they found needles in the oil but they needn't worry as the pieces are too large and are trapped by the screen on the oil pump. All you do is replace the offending rockers then change the oil.

With really bad case of guide wear, all the valves in the engine, of one or both types, will make noise.

The part in the article about Linamar going to 100% inspection was in re: continuing production, not going back and checking heads already manufactured. Linamar was making heads for a while, even after the LS7 went out of production, for GM Performance crate engines and for future replacement parts.

My guess is your '13 is ok, but even if it's not, you don't have enough miles on it to make testing useful. You need 10,000 miles or more on the engine before I'd invest in a preemptive removal to measure stem-to-guide clearance.

As for competency to do the checking...remember, this is not rocket science. The engine is still a Chevy V8 and the methods of checking stem-to-guide clearance are well understood by good machine shops. Any reasonably good dealer can pull the heads off the engine. Any decent facility which does head work should be able to do the measurements.

Of course you could avoid any/all potential problems by taking the heads off and sending them to West Coast Cylinder Heads for porting. When WCCH does your heads, they'll put in CHE guides and finish them properly.

Also, I just noted your 13 Z06 is 1LZ which is a relatively rare car. What color is yours?

My '12 is a Carlisle Blue 1LZ.

 

[Iroc2Vette]

I understood the inspection wasn't retroactive. But, thanks for clarifying...Honestly, I just wasn't sure.

The dealership I've been using has been pretty good to me. Partyka in Hamden, CT. They've allowed me to bring in my own oil and even brake parts (Delco) from Rock Auto. The dealership won't warranty the parts, but, they'll warranty the labor. People are always shocked when I tell them I can bring in my own parts. So I might go to them or this other place very close to me, Mild To Wild, which specializes in modified performance cars.If I ask them to send out the heads to a specialist, I don't think that'll be a issue. I appreciate the mileage recommendation. It gives me something to really ponder. It's almost like buying a extended warranty plan way out in the mileage. Which would cost quite a bit. Probably as much as to get the heads redone.

If I remember the numbers, there are only about 64 Z06 with the 1LZ. I factory ordered mine. That's why. I don't think Chevy built any for speculation.

The color is arctic white. Again, a rarity for the Z. I think only 128 were painted this color.

And, a friend of mine owns a red 2008. We both agreed how much we love the 427s. He was a former Ferrari 360 Italia owner. He just sold it. Said it was a terrible expensive PITA to keep.

I really like blue. The Carlisle is a great hue. I would've like that color as much if not more. I got the white for several reasons. My IROC was white with ebony interior, it seems easier to maintain and chip repair, it's a 60 year anniversary color, and, most of all, it's a no extra charge color. I was really stretching myself to get this car at the time.

I received my car on Oct. 4 of 2012 for the 2013 model year. It took about month for the entire inventory collection and build process. I got to watch the progress bar on Chevy's web site. Wish I could've built my engine like you did, though. THAT would've been a bucket item for me...