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  1. #16
    Member Iroc2Vette's Avatar
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    Quote Originally Posted by L over D View Post
    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 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...
    "Aerodynamics are for people who can't build engines." -Enzo Ferrari

  2. #17
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    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

  3. #18
    Member Iroc2Vette's Avatar
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    Quote Originally Posted by Hib Halverson View Post
    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.
    "Aerodynamics are for people who can't build engines." -Enzo Ferrari

  4. #19
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    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.

  5. #20
    Member Iroc2Vette's Avatar
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    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...
    Last edited by Iroc2Vette; 09-28-17 at 09:39 PM.
    "Aerodynamics are for people who can't build engines." -Enzo Ferrari

  6. #21
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    Default errata.......

    toms 007 said..........

    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.

    ...........................
    well thanks for the kudos.........reason I came to CAC is it is a cut above. After seeing/reading all of Hib's writings I thought right. I have had a few Corvettes in the last century. Now I have been lurking and looking to buy another in near months....C6 or C7.

    Now that I did some digging, and found that the LS7 cylinder head design and longevity was subject to my scrutiny (IMO), I should be prepared to pull things apart at some time after I buy. I found here and elsewhere a trove of information....and discarded the MIS-information. What I believe after two weeks of reading and looking on the designing of the LS cylinder heads with the LS7 package to deliver OVER 500 hp was a mighty goal 13 years ago. Very possibly the GM politicians pressured the 500 + and more possibly Ti valves, lash caps and more exotica. And numbers and goodies sells cars. I might think that using Stellite or even stainless valves would mean using higher valve spring numbers. back then in the dark ages Ti was magic ! So backing down the packaging would only deliver...400....450 ?? but with better longevity. But maybe I'm wrong. More displacement? Maybe. You cant have guns and butter. When you move into high gear production , as was West and the outsourced 5 axis machine company, it must be to tenths not inches when you are putting out a 500 hp street car. I still will be buying a Corvette.

  7. #22
    Valve guide wear on ZO6 427 engine Tuna's Avatar
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    LS7 Work - maybe, maybe not
    Depends on the engine, the year, miles and whether the heads have already been worked on.
    It seems that by 2013, the LS7 heads were no longer an issue. I have 48,000 miles on my LS7 and it hasn't missed a beat or rattled or done anything else but scream to redline and ask for more.
    Tuna
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  8. #23
    Member Iroc2Vette's Avatar
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    I'm heading toward 60K, rapidly. And mine is also a 2013. And, both oil test samples had zero wearable metals in the oil, even after 8Kmi oil changes. In fact, Blackstone said I can easily go over 10K.

    But, my car may've been made early enough in 2012 where I might've gotten a set of older heads in inventory. Since the inspection process isn't retroactive, it's a bit like having a sword dangling above my head. My PT warranty goes bye-bye Oct. 4rth, 2017. That's 2 days from now.

    I'm assuming, or speculating the new heads will cost about $2-3K. Maybe a bit more. But, compared to a $21K+ new engine, it's looking more like good preventative maintenance. The owner of the shop said it might be more cost efficient to just buy a set of HP heads (Trick Flow, Brodix, RHS, Texas Machine, Dart, etc.) than to have them shipped out and back and the machining, disassembly/reassembly...But, he's got to look more into it.

    If it's workable, it might be possible to install heads which might give even better performance (25-40 more bhp), as long, and ONLY as long as the OE intake manifold and headers bolt up and work properly. And no engine check light DTCs. Any change in drivability the way I have now will be unacceptable. Especially getting stuck in traffic. I need lots of idle range torque for clutching.

    What I'm also thinking of as long as the top of the engine is being broken into (yech!!!), I might as well also get top notch lifters, rods, rockers and springs. The parts cost little and as long as the heads are off, so will the labor.

    Geezzz! I was SO hoping NOT to have to do this...
    "Aerodynamics are for people who can't build engines." -Enzo Ferrari

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