lowcountry

iTrader: (1)

I have a couple of active threads going about the LS7. In each one, the problem of pre-mature valve guide wear keeps popping up as a major issue. So I decided to start a new thread about this.


When I started researching crate LS engines to put in my 70 Z28, the LS7 surfaced as the most reliable with the most HP. I wanted something I could drive on the street without any issues. I read one article that talks about the endurance test the LS7 goes through. It is pretty brutal. Now I am hearing from members about major valve guide issues that require re-worked heads at some point not to far down the road.


I have no reason/evidence to doubt what is being said, but how come there is no outcry from all the new 2014/2015 Z28 owners that have the LS7? You would think that if it was such a major problem that GM would be hustling to fix the problem...and the media would be all over this.


I am getting ready to spend a lot of $ on an LS engine and I really like what I've learned about the LS7 - except of course this valve guide thing...


I have heard from a couple of people with real world experience on both sides of this argument. I appreciate the input - but it has been confusing and contradictory at best...

FLYZNTN

I know that GM acknowledged they had an issue back in 2013:

LS7 Heads Valve Guide wear WCCH Fix

I'd imagine that by 2014 they would have corrected the problem for the new Z28.

Still, if I were to build an LS based 427 (4.125 bore) with LS7 based heads I'd make certain I did two things minimum.

1) I'd use an LS truck block re-sleeved with new ductile iron sleeves (Not much more than a new LS7 block).

2) I'd buy aftermarket LS7 heads or have WCCH rework an OEM pair

Piece of mind is worth the extra expense in my opinion.

lowcountry

iTrader: (1)

Thanks, interesting read and I do appreciate your comments.


The whole point of my initial adventure into the LS world was to buy a crate engine and go from there. I have zero experience with the LS platform. If this were a 1st gen sbc, issue, I would have no problem pulling the heads, having them modified, and re-installing. I have built many 1st gen sbc engines. I did not want my first LS engine to be a work in progress.


I would prefer a plug and go engine to start. I might be naïve in my thought process, but I thought that spending $15K+ for a crate engine would support my needs. I can build 3 1st gen engines for that that price.


Anyway, I'm just trying to learn. I don't mind spending $ to get what I need - just not rich enough to sample all the options.


You made a comment about the 2014 engines maybe being corrected. I was wondering/hoping for the same thing. I wonder how one goes about verifying this...

KiwiKid

Way to go Flyn,

You probably already know thats exactly what I did, except I chose to go the MID wet sleeve route with Steve at RED, Racing Engine Developments. I also chose Richard at WCCH, West Coast Cylinder heads.

I talked to just about every body over many months and figured that for $3,500, using the strongest off the shelf LS Aluminum engine block that GM has made to date, the GEN4 5.3 truck engine, had to be the best basis for a tough engine build.

For a road race engine you need to keep the port runner size down and the best flowing cylinder head I found to do that was the 285cc Pro head that Richard helped develop and finish ports.

Cheers,

Mark.

FLYZNTN

Hey Mark,

Yes. I did read that you went that route. You are a wise man with a really cool race car
When I first started looking at doing a new motor I thought I'd do a 427. I am running a supercharger so research told me that the stock LS7 sleeve wasn't the way to go. A little more research and, lo and behold, a 5.3 truck block with new ductile iron sleeves can be had for only a couple hundred more bucks than a new LS7 block.

So, better and longer sleeves for only a little more = no brainer IMO.

As far as the heads, stock LS7 valve guide issues are fairly well documented so it would be aftermarket or rebuilt with different valve guides if I were to go that route.

The irony in all this is that I eventually did none of these things. I went as far as buying the block but discovered along the way that I really needed more blower to run that many cubic inches. I didn't want to buy a new blower so I went with an all forged 377 and gave the block away. LOL!

Fraser588

On what Planet

Here's a list of issues:

Ti rods being scored on the big ends
"Ti Dust" as the TSB calls it from the rods getting embedded in bearings
3 pc Exhaust valves breaking apart
Cracked pistons
Cracked liners
worn valve guides
Rocker arm needle bearings falling out (I know its an old issue)
Oil pump runs out of oil flow because of Z06 tank design. (I know separate from engine)
Rocker Pedestals.... why change it?

So yeah I'm sure the LS7 could pass a 50 hour GM durability test, but beyond that... At 3000 hours it needs a full out of frame rebuild with new rods, valves and guides.


That's an LS3

KiwiKid

Hi Fraser,

I think most of the LS7 issues you raise, and you missed a big one [Wrist Pins tearing them selves out of the Hyper-eutectic cast pistons, on a missed gear change, which is a real big issue when you road race these engines] are caused by GM's unbelievably wide "acceptable tolerances" from their vendors.

We blue-print brand LS7 new crate, or long engines, and change out the parts that we don't think are reliable enough for our application, which is the option to use a steel rotating assembly [not because there is anything wrong with the crank, it just's less expensive to buy the complete, and fully balanced kit in bulk from Callie's, to suit the low cost "off the shelf" Mahle Forged pistons] and change out the OEM parts. Personally I would only change out the Hyper-eutectic piston's as they are not fit for purpose components.

Now this is the part were we, V8ST, differ from almost all posters on this thread, the only thing we change on a brand new set of cylinder heads, is the Rocker trunnion, not because we have had issues with the needle rollers, we just think they are an obvious weak link.

As I have said several times before we have never seen a dropped valve ever, so why change them.

We have seen worn valves, we have seen split cylinder liner's but only rarely, none of our engine are older than 2012, most are 2013 built engines. From 2013 the long block [Service engines] all had the modified pistons and little end's re-profiled to suit the revised piston's. I am unaware if a brand new latest 2015 build full LS7 crate engine engine yet has these revisions because now days we only ever by the so called Service engine.

I believe that the so called issues such as the worn valve guides and dropped exhaust valve's are real, but blown out of proportion by engine builders because they only get to fix or rebuild a very small number of the LS7 engines that exist out in the market place were thousand of these engines never give a problem for many years and tens of thousand of miles.

I am a huge fan of the normally aspirated LS7 engine when its blue printed with the right tolerances, and forged piston's etc. Yes, I know you can build a better mouse trap using the LS architecture, but to build something brand new better than an LS7 crate engine, cost's a lot more money.

erick_e

As the owner of a LS7 who had my heads replaced due to this issue, I recommend that you peruse the C6 Z06 at corvetteforum.com

There are so many theories on the root cause of the issue and not one definite answer on why. Some people say the hollow stem valves are weak, others say the heads are cast correctly creating a rocker arm geometry issue, some say its because of the valve guide material, others say the valve seats are not concentric, and some say the valve guides are too loose from the factory. And some say may be a combination of one of more of those issues.

Having had three sets of heads myself, a lot of research, and my experience I believe that some heads had loose guides and/or concentricity issues from the manufacturer which caused the hollow stem valves to bounce.

I don't think you will have any problems if you have the heads machined by competent shop before installation.

KiwiKid

Hi Eric,

Like I said above, I don't doubt there have been issue's, however I think you will agree that in a forum such as this we are somewhat myopic, in our views, and the internet allows us to make a loud noise about such issue's.

Its not like thousand's of people right letters to the editors complaining on a national new's service about the issue. Its confined to the very small percentage of car tinker's amongst the vast consumer majority that would not even know what is under the hood.

If it was really a big issue, the Lawyers would have whipped up a Class action against GM right now, and the fact that they have not puts it into perspective, at least in my view.


Cheers,

Mark.

Exidous

iTrader: (11)

Manufacturing issues with the LS7 aside, which have been fixed since, there are logistical problems with the LS7. Mostly the dry sump oiling.

An LS3 525 crate motor has 20 more hp than an LS7 and wet sump oiling plus a GM warranty. Bolts up pretty much exactly the same as an LS1/LS6/LS2 minus the 24x/1x and 58x/4x thing.

The LS7's had different issues as the years went on. I'll only mention things that I've found that have been confirmed by GM. Early heads had the rocker stands machined improperly and caused the rocker geometry to be wrong. Mid year engines had valve seat concentricity issues on the exhaust. Later years on the intake. All off these were faults of Linimar. The contractor for GM to machine the heads. They could just not seem to get everything right with the LS7 heads for some reason.

I've personally been looking at having my LS1 sleeved and bored to 4.125 and building my own non LS7 427.

You can find LS7 rotating assemblies for 1000-1500. Turn the LS7 crank snout down .901" and it's just like an LS3 crank. ~2500-3000 for the sleeving plus the block cost.

Under 4k for an N/A beast capable 427. Certainly wouldn't boost it though.

lowcountry

iTrader: (1)

Are you talking about dry sump oiling in general or the system on the LS7? And if LS7 specific, what is the problem?


Also, could you elaborate on the 24/58 "thing"?


thanks.

Exidous

iTrader: (11)

It's not LS7 specific. Dry sump in general. Some frames don't allow for the oil pan as it's deeper at the front than the f-body pan. Plus the routing of all the lines and tank.

There's nothing wrong with the dry sump of the LS7 as long as you can package it into your chassis.

With the 24/58 I'm talking about the crank reluctor and camshaft timing. Gen III uses a crank/cam 24x/1x setup and the Gen IV uses a 58x/4x setup. The gen IV has more resolution obviously but is not compatible with older LS1/LS6 PCM's without an adapter box from Lingenfelter.

Fraser588

Indeed, found my own LS7 long block in the classifieds, two cracked pistons from N20. The rods appear reusable. Unfortunately many tear down an LS7 to find the rods are junk. The crank needs heavy metal if you use steel rods, expensive balance job.

Exidous

iTrader: (11)

There was/is a set right now asking for 1k plus shipping. It's very temping.