LS7 Head Valve Guides
Thread Starter
Joined: Jul 2014
Posts: 10,451
Likes: 1,873
From: My own internal universe
LS7 Head Valve Guides This quote was in a different thread, but there was so much else going on in that thread, I thought it better to start a new topic vs triggering the argument
Then, today, I read this over in Corvette Action... it's an older article going over the history of the LS7. The main point I'm bringing up is this:
So, with that information, there is no material that is going to correct the issue. When the valve seats, it is going to side-load the valve, and whent he valve lifts, it is going to center-load the valve.
So, my question -- Has the aftermarket corrected the issue? In other words, if one purchases aftermarket LS7 heads that are also aftermarket castings, has the error been corrected? Or, were the heads reverse engineered around the error, so it has been copied forward into all the aftermarket versions of the LS7 head?
it would be a terrible shame if this did happen, as the head is a very forward looking design in its day.
Guys I've been posting about the ls7 head issues for years if those are ls7 style heads...their is not a fix...I've seen my own heads out of spec 3 times now...I just pull an replace guides every 15k. I've seen the wear in all heads from all diff shops, check your valve guides guys. so called fixed heads or aftermarket heads isn't a true fix...will last longer but the guide wear will be there. if this is a cathedral or ls3 style head then disregard my post because those are fine
Lack of concentricity, also known as "valve seat run-out", is caused by inaccurate machining of the cylinder heads .... the nature of the inaccuracy is valve seat centerlines and valve guide centerlines, which are not concentric
So, my question -- Has the aftermarket corrected the issue? In other words, if one purchases aftermarket LS7 heads that are also aftermarket castings, has the error been corrected? Or, were the heads reverse engineered around the error, so it has been copied forward into all the aftermarket versions of the LS7 head?
it would be a terrible shame if this did happen, as the head is a very forward looking design in its day.
Usually when a valve job is cut, the cutter is indicated off the guide centerline using a pilot. If the eccentricity is the issue, a valve job by a competent machinst would fix it. The flaw isn't necessarily in the design of the head which could find its way into the aftermarket. It’s a poor manufacturing process.
Serdi Valve Machine Hi Jake, I run LS-7 heads in off road race engines.
I had Sheldon install my Induction Hardened Steel Guides using his Serdi Machine AND machine the seats.
The Serdi "centers" on the guide with seats cut concentric.
I assemble the head myself AND use Titanium Dioxide (tooth past) to mark seat angle.
I have found errors, not often, with "rework" required.
I do not "lap" seats with SAND.
I do not know why the "truck" head would be different than ANY OTHER cylinder head ?
Lance
I had Sheldon install my Induction Hardened Steel Guides using his Serdi Machine AND machine the seats.
The Serdi "centers" on the guide with seats cut concentric.
I assemble the head myself AND use Titanium Dioxide (tooth past) to mark seat angle.
I have found errors, not often, with "rework" required.
I do not "lap" seats with SAND.
I do not know why the "truck" head would be different than ANY OTHER cylinder head ?
Lance
Usually when a valve job is cut, the cutter is indicated off the guide centerline using a pilot. If the eccentricity is the issue, a valve job by a competent machinst would fix it. The flaw isn't necessarily in the design of the head which could find its way into the aftermarket. It’s a poor manufacturing process.
The run-out can be easily corrected through proper machining of the valve seats, weather using a pilot or a CNC machine.
The increased wear mentioned by z0sicktanner has nothing to do with the dimensional design/layout of the head (factory or aftermarket) and has everything to do with the quality of the machining, application usage, component material, etc. Increased wear will be present when using today's aggressive camshafts, valve springs, etc.
I think one of the biggest contributors to LS7 valve guide wear is the fact that a lot of people run more aggressive camshafts (me included) with stock rocker arms that have additional "scrubbing" across the valve tip which directly contributes to increased valve guide wear. Using a roller tipped rocker arm can help the situation if the geometry is properly setup.
Do I EXPECT my guides to last 100K miles, no. Do I need to check them more often because it is a "performance" engine, yes.
I agree. Regardless of cylinder head type or manufacturer, valve seat run-out applies to all.
Thread Starter
Joined: Jul 2014
Posts: 10,451
Likes: 1,873
From: My own internal universe
Thanks guys. really appreciate the info.
I had not thought about the re-machined valve jobs correcting the run out. For example, I would consider Lingenfelter a pretty competent shop, and since they did the valve job, i think I can put eccentricity to rest.
If / when I pull these heads, I likely will do the cast steel guides. i like the intrinsic lubricity of bronze, but from what I read, the valves are breaking from guide wear. The steel guide - even very mild steel - will wear far less vs a bronze guide
Also, Cole, I agree roller tips are better to avoid the scrubbing, though I think lash caps helps the situation a little by giving the rocker a very smooth surface to be able to move against. Scrubbing concerns is the reasons I opted to keep my cam lift under 650. that said, it is still LLSR, so it is aggressive ramp rates.
You know how sometimes a thought can really get stuck in your head? That's kind of what happened. Thanks for helping me breathe a great big sigh of relief.. 
Usually when a valve job is cut, the cutter is indicated off the guide centerline using a pilot. If the eccentricity is the issue, a valve job by a competent machinst would fix it.
I had Sheldon install my Induction Hardened Steel Guides using his Serdi Machine AND machine the seats.
The Serdi "centers" on the guide with seats cut concentric.
The Serdi "centers" on the guide with seats cut concentric.
I think one of the biggest contributors to LS7 valve guide wear is the fact that a lot of people run more aggressive camshafts (me included) with stock rocker arms that have additional "scrubbing" across the valve tip which directly contributes to increased valve guide wear. Using a roller tipped rocker arm can help the situation if the geometry is properly setup.
Do I EXPECT my guides to last 100K miles, no. Do I need to check them more often because it is a "performance" engine, yes.
One thing that nobody mentions is faulty guides themselves. I have personally seen guides where the inner diameter isn't concentric with the outer. When the guides are drilled and then reamed, the drills and reamers follow the original hole. Since the final valve seats and guide are machined with the same tool, the seats are in the proper place, but with bad guides, the guides won't be concentric with the seats.
One thing that nobody mentions is faulty guides themselves. I have personally seen guides where the inner diameter isn't concentric with the outer. When the guides are drilled and then reamed, the drills and reamers follow the original hole. Since the final valve seats and guide are machined with the same tool, the seats are in the proper place, but with bad guides, the guides won't be concentric with the seats.
Trending Topics
Teching In
Joined: Jun 2017
Posts: 15
Likes: 0
From: Central Texas
A proper valve job will fix the concentricity issue. There are a lot of variables as everyone is well aware of, that can exacerbate the original issue and/or even create new issues. This is in part why we continue to see "issues" with the LS7. Let's face it, folks are piecing together parts here and there on thousands of different builds, and it's sort of become akin to a big chili cook-off with as many different recipes. Some good, some not so good.
As much as valve lift is a factor, so to is the design of the cam lobe on the overall general wear of the valvetrain. An aggressive lobe on top of high lifts (which for an LS7 is generally > .650") will wreak havoc on any LS motor in general, and in particular an LS7 valvetrain. If you look at the COPO cars for 2018, I think they have a good recipe going: Johnson hydraulic lifters, PSI valve springs, and a CamMotion camshaft. Of course, they're still using Ti valves on PM guides which is generally not the preferred solution when using Ti valves. And if that head was machined by Linamar (like every other GM LS7 cylinder head) then there is a good chance those guides (or at least one, and all it takes is one,) are not concentric.
The closest one can likely get to a sure-fire solution to the LS7 valve guide issue is a proper concentric valve job using a superior exotic alloy like CuBe, or even better Moldstar. AHP has taken the time to craft an LS7 valve guide out of Moldstar 90 and it has the best of both worlds in terms of thermal conductivity and hardness/durability.
http://moldstar.com/MotorsportApplications.htm
As much as valve lift is a factor, so to is the design of the cam lobe on the overall general wear of the valvetrain. An aggressive lobe on top of high lifts (which for an LS7 is generally > .650") will wreak havoc on any LS motor in general, and in particular an LS7 valvetrain. If you look at the COPO cars for 2018, I think they have a good recipe going: Johnson hydraulic lifters, PSI valve springs, and a CamMotion camshaft. Of course, they're still using Ti valves on PM guides which is generally not the preferred solution when using Ti valves. And if that head was machined by Linamar (like every other GM LS7 cylinder head) then there is a good chance those guides (or at least one, and all it takes is one,) are not concentric.
The closest one can likely get to a sure-fire solution to the LS7 valve guide issue is a proper concentric valve job using a superior exotic alloy like CuBe, or even better Moldstar. AHP has taken the time to craft an LS7 valve guide out of Moldstar 90 and it has the best of both worlds in terms of thermal conductivity and hardness/durability.
http://moldstar.com/MotorsportApplications.htm
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Simply has to be a factor when the rocker shape puts the push rod energy out of line with the valve tip
now elevate the lobe flank speed, overall valve lift, and rpms.......seems like the perfect storm to EFF’d up ****
now elevate the lobe flank speed, overall valve lift, and rpms.......seems like the perfect storm to EFF’d up ****
Copper seats/guides Hi BigVet, I have worked with Copper guides/seats used in Cosworth Race engines for BEST heat transfer.
These engines are OFTEN "freshened".
I found MANY cures NEEDED to increase engine life in the Oil Field/Natural Gas Engine.
We fit Stellite Faced Valves/Stellite Seats AND Steel Guides in this type of application
Stellite works very well in high heat engines.
The choice is mandated by the users expected engine life, time between rebuilds.
Lance
These engines are OFTEN "freshened".
I found MANY cures NEEDED to increase engine life in the Oil Field/Natural Gas Engine.
We fit Stellite Faced Valves/Stellite Seats AND Steel Guides in this type of application
Stellite works very well in high heat engines.
The choice is mandated by the users expected engine life, time between rebuilds.
Lance