Valve Stem Tip Spalling

[Mark200]

While addressing the worn valve guide issue in my stock LS7 I've run across multiple examples of spalling on the valve stem tips. On a stock engine(s). Any ideas why this would be occurring on a production line engine?

One thing of possible concern to me (as an enthusiast, not an expert or professional) is that the stock beehive valve spring seems to be set up within .050 of coil bind @ max spec lift (and by coil bind I mean total stack up of all coils... total compression of the spring). Spec install height 1.959", lift .590", coil bind 1.304". After a valve job my install height measures 1.945" (OEM valves) (did not measure prior), which will put me within .051 of coil bind at max lift. I realize that .050 is the oft-touted target but given that coil contact is occurring between at least some coils well before total bind, and given what I see in the photos, may it not be better to adjust the install height (or use a different spring) to stay farther away from coil bind? Like .100? At least?

Following photos from a 50K mile stock LS7 engine:

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Following photo from a 44K mile stock valve (from a stock LS7 engine):

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[dstaff]

It's possible the stem tip wear could be a symptom of the valve guide issue you mentioned. I would not try to increase the installed height of the springs. On some beehive or progressive rate springs, it's not uncommon to start seeing coils touching well before max lift. As long as you have the right spring pressures for the cam and RPM involved, I would be happy with the .050" distance to coil-bind. If you were into coil-bind, you'd likely see broken springs and bent pushrods before you saw galled stem tips.

[nickmckinney]

See if you can have a hardness test done on the tip of the valve. A beehive can coil bind progressively depending on its shape, I don't have a problem with 2 coils touching but 3 or more can start getting dicey on a street motor.

[Strange Magic]

I would venture to say that it might be as simple as the lack of protective components that should be in the oil.

You mention LS7 engine. If it's an oem style LS7 engine and your lacking the fuel necessary for it to be happy and content, then excessive heat from detonation can be absorbed into the valve train.

[Mark200]

Thanks for the insight on the bind issue, sounds like I can dismiss that as a concern.

As to the heat issue, something of note is the tendency for these engines to prematurely wear out the exhaust valve guide (clearances in the .010 range and up seem to be turning up with some frequency), which I think we can presume allows the sodium filled exhaust valve stem to overheat (the spalling is only seen on the exhausts, but then the titanium intakes wear a lash cap). I wouldn't have thought that the excessive heat would get all the way to the tip, but offhand I can't see why not.

The factory fill for these engines is Mobil 1 5W30, which doesn't seem to get rave reviews.

[dstaff]

Strange mentioned having the proper fuel... Nothing about what type of oil.

I've only been into two sets of LS7 heads, but both of them had the worn guides and exhaust valve stems. I'm not sure exactly why they seem to have that problem.

[dstaff]

He did mention oil. My bad, ignore me

[The Radius Kid]

I'm looking at the tip of that rocker arm and the factory finish looks horrible to me ... as cast,if my guess is correct.
I'm not surprised the valve tips get chewed up with something like that riding on top.
It looks like material from the valve tip is depositing or welding itself to the tip of the rocker arm.
Maybe carefully go over the rocker tips with a honing stone to smooth the factory mess?
BTW,don't they have the same problems with the tips of the valves on the late model Hemis?

[Mark200]

My guess is that the spalling is a result of extreme pressure (cracking). Just can't figure out what might cause the pressure (was thinking perhaps running close to coil bind, but apparently not). Alternative might simply be the use of a pad type rocker @ ~.600 lift, altho I hear that's supposed to be within reason. Last guess is that with worn guides the geometry gets out of kilter and spikes the pressure between the rocker pad and the stem tip as the stem wanders around during operation.

I don't recall any intake valve tips showing the same type of wear, which would tend to exonerate the rocker, but the intakes do use a lash cap which simply might be harder/smoother material than the exhaust stem tips (also the intake guides usually don't get as far out of spec as the exhausts, by about a factor of 2). At high magnification the tips of the exhaust valves look really bad brand new, but given my very limited experience I don't really have anything to compare them to, finish-wise.

New untouched LS7 OEM exhaust valve tip (disregard black ink marking):

. . . .

My understanding is that the rockers are investment cast and have been used on pretty much all small block Chevys for the past 10 years or more.

I glossed over the fuel comment since I've rarely seen or heard of any detonation issues on stock engines (broken piston ring lands, damaged spark plugs, etc).

[lorax]

BTW,don't they have the same problems with the tips of the valves on the late model Hemis?

yes. Yet factories will insist none of it has anything to do with GF5 approved oils.
So when it exists, what does that leave? Poor design, or poor materials?

[Strange Magic]

I wouldn't give Mobil 1 oil to my worst enemy. It's just my thoughts on a product that had much better days years ago. To be blunt, it's shit! Just my humble opinion.

That picture you show, of that crude finish on a brand new valve, is just remarkable. It either belongs in the garbage or needs to be finished properly. That seems like a stone that was either dressed with a diamond, finished incorrectly and compounded with an operator that just could care less, and Stevie Wonder on QC.

P.S. It can't be to darn magnified if the whole tip is in the picture.

[user-3597028]

Run a true performance oil with an additive package including zinc. This problem will most likely go away.

There are still places in engines where zinc is required. Unless you put a roller rocker on the engine, this is one place that needs help from the oil. Even then, a roller rocker only transfers the metal to metal load to a axle pin, but it helps.

I use Synergen products. Their oil additive or oil will eliminate this problem. If it doesn't, there is oil system issue.

[crazyman]

As cast rockers and rough cut valve tips would be my guess.. Must we tear apart a brand new engine to "freshen it up" GM?

As far as coil bind.. I'm definitely not a professional, but when was the last time you pulled out your feeler gauge and saw how thin even 0.100 is? Imagine it at rpm crashing coils while oscillating multiple times per cycle..

[lorax]

I wouldn't give Mobil 1 oil to my worst enemy. It's just my thoughts on a product that had much better days years ago. To be blunt, it's shit! Just my humble opinion.

Its not all crap. You just have to know which are, and which aren't. They along with all the other oil manufactures/marketers were required to make less than favorable changes to their oils to meet certain specs. Some Mobil 1 oils like their 5/30 is less than it could be. Don't blame them, blame the EPA and ILSAC(auto manuf). I wouldn't run Mobil 1n or ANY GF5 certified oil in a lawn mower, let alone a performance engine specially once its out of warranty.
I run Mobil 1 in a blown BBC in an edurance boat, and never had a single issue. But then I am not trying to run some oil dictated by the EPA and auto manufs.

Run a true performance oil with an additive package including zinc. This problem will most likely go away.

There are still places in engines where zinc is required. Unless you put a roller rocker on the engine, this is one place that needs help from the oil. Even then, a roller rocker only transfers the metal to metal load to a axle pin, but it helps.

I use Synergen products. Their oil additive or oil will eliminate this problem. If it doesn't, there is oil system issue.

Yep. No matter what the auto manufactures think, they did not rid the entire engine of parts and places that an GOODm anti wear agent is needed. This is just one of those places. I laugh when people look at their mains and rod bearings and judge their oil by that. Wesson oil would work fine for a pressurized plain bearing. Castor bean vegetable oil ruled Indy during the Offy years.
What you are seeing here is perfect example of an oil that cannot do the job it is required to do. I have no doubt the problems with the guides is partly due to the same thing. JMO

As cast rockers and rough cut valve tips would be my guess.. Must we tear apart a brand new engine to "freshen it up" GM?

As far as coil bind.. I'm definitely not a professional, but when was the last time you pulled out your feeler gauge and saw how thin even 0.100 is? Imagine it at rpm crashing coils while oscillating multiple times per cycle..

The only way you can coil bind a spring that has .050-.060 clearance in a running engine is if the valve is lofted off the nose. If thats the case, and it is entirely possible, then he has big spring issues. But if this is a STOCK engine as he posted, I doubt that is the problem unless he is running it into valve float.
I would not be at all surprised to see the same exact results from spring hysteresis/surge/harmonics. But not with a stock cam that wasn't subjected to valve float repeatedly.

[crazyman]

Thank you for teaching me a new word. Hysteresis.

OEM or not, valve springs are probably the most important part of any engine. Look at stock dodge magnum springs.. Any spring that can be compressed by hand easily is not optimal, yet dodge still authorized it. Make the springs too close with rough valve tips and un machined rocker pads? Disaster... Any excessive bounce is unacceptable in my book.