Darth_V8r

iTrader: (4)

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.

KCS

iTrader: (20)

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.

pantera_efi

iTrader: (1)

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

ColeGTO

iTrader: (3)

I agree 100%. Poor manufacturing process that caused the run-out. Also, either an inadequate inspection process (detection) or improper tolerance (acceptability limit) allowed the issue to go unresolved.

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.

Darth_V8r

iTrader: (4)

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..

farmington

iTrader: (14)

KCS

iTrader: (20)

That is why the valve job is cut after final machining of the guides.

BigVette427

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

A.R. Shale Targa

iTrader: (2)

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 ****

pantera_efi

iTrader: (1)

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