Well everyone this is my first post, and I'll admit that I joined the forum just to post this. I recently picked up a L9H for a ls swap into 77TA. The plan was to tear everything down, get it hot tanked, possibly painted and rebuilt with a decent cam setup. I'm sitting hear looking at the underside of the passenger side head and can't quite make sense of what I am looking at. As I have been tearing into this engine it seemed that it had never been torn down before but looking at this valve seat I'm trying to understand if someone did a really bad install of a new seat. Or, is this seat at one time dropped and then was hammered back into place by the valve/piston. This same valve did contact the piston a couple times for added forensic data.

Have any of you ever seen this before. I am assuming this is not worth repairing but I'm interested in everyone's input.

 

It's a damaged valve seat and can be repaired but it may just be cheaper to source another cylinder head.

 

There's nothing wrong with that seat at all. Looks perfect to me. No sign of it ever having been out.

The marks are in the aluminum casting around the seat. In fact looks like it might even have ran like that at least for a little while. Totally harmless except for whatever extent they may get hot and cause preignition which I doubt would be very much. You can clean em up with a Dremel or die grinder if they bother you. They look like they came from a valve that dropped and got bent but didn't break. What did that valve look like when you took it out? What about the spring?

 

Guess there's nothing wrong with this either.

 

That one has a bit more wRong with it.

The OP's seat however, isn't hurt.

 

I didn't really think there was anything wrong with the seat, and the valve looks fine as well. What I'm really worried about is that something clearly happened, I am confident GM did not make the head that way. I still think I am the first person to tear into this engine, so my best theory is the head got hot enough for the seat to drop out, and then when the valve closed, it captured the seat at an angle. The piston then came up and mashed the seat into the head. It might be hard to see in the picture but there are circular grooves in the head above the seat. Somehow, maybe on the next intake stroke the seat aligned itself back into place.

It seems really unlikely but I can't think of another explanation, and if that is what happened I don't want to run the risk that it may happen again. Fortunately the guy who sold me the engine offered to exchange the heads with a set of 5364 heads. He looked at the head and was just as confused as I was.

 

Yes something clearly happened.

No it wasn't that the seat fell out and the piston pressed it back in in the exact perfectly right place as if nothing ever went wRong. Even if the piston could reach that point, that's about as likely as dropping the shards of a broken piece of glass on the floor, and them miraculously reassembling themselves into the pristine glass artwork they once were. Right on up there with the space aliens abducting your car and returning it like factory-new except with 1000 more rwhp or implanting an Elvis sighting into your paint job.

Yeah right. Let's stick with what can ACTUALLY HAPPEN in The Real World.

What happened was, the valve dropped; the piston hit it and bent it; it then hammered the head casting next to the seat, but didn't damage the seat in the process; and somebody replaced the valve and the spring without removing the dents in the casting.

Did the valve and the spring match all the others?

 

I wouldn’t be a bit surprised if that head left the factory that way. QC is crap. You guys wouldn’t believe the horror stories and pictures that I’ve seen and heard from dealership owners regarding warranty work involving a new engine. Only a couple variants of these engines get built by hand, with human eyes on them. Millions and millions get built by robots. There is a QC checkpoint along the way in many steps, but stuff happens….especially when punching out millions of engines very quickly.

 

The valve looked unremarkable, no damage and straight. Spring was the same, you couldn't tell it from the rest in the head. Both of the above are likely. The engine was pretty filthy everything looks original so I think it is more likely it was built that way from GM than someone replaced the valve. Here is what the piston looks like. I'm not expert but it looks pretty minor to me.

 

If "it was built that way", seems pretty unlikely that it would have left marks on the piston. Only way a piston gets valve marks, is if a valve drops.

The plot is becoming clearer. The valve dropped. Then, based on the valves & springs all being the same and old, somebody replaced the valve with another stock one (probably the machine shop doing the work just pulled one out of an otherwise trashed head core) and put all new springs on it, a long time ago.

Note of course that the seat is smaller than the valve in any case; even if it had somehow fallen out, it can't get past the valve to the piston, and if it did, the piston can't put it back with the valve in the way and then put the valve back TOO, unless you've got some really special pistons. The whole seat-fell-out-and-the-piston-put-it-back proposed "explanation" is NOT POSSIBLE in The Real World. Especially since there's nothing wrong with the seat to begin with.

"The simplest explanation that fits all the facts is most likely to be the right one". "Simple" means the least number of several bizarre coinciding 1-in-a-million events all happening at the same time, strict adherence to the laws of physics, discounting alien or divine intervention, taking typical repair procedures and the like into account, and so forth. Stick with SIMPLE. Although, in The Real World, those marks on the head casting are of virtually ZERO consequence, as evidenced by the fact that it already ran like that for however long; any "explanation" at this point is merely for the satisfaction of curiosity, and has little or no bearing on any Real World decision-making for the future, beyond possibly cleaning the marks up a little.

 

Seats coming loose in 6.2L 823/821 heads is not unheard of. I have seen several. Had it happen to me also on a customer's engine (bad deal) I ate a 6.0L LS2 block and pair of 821 heads with light valves.

I am not 100% of the cause as I have not seen it happen until 100K plus on certain heads. They obviously lasted a long time. And I have seen it on 40K engines. The set I did I had a cut a valve job on and surfaced. They were NICE 'cores'. No sign of a seat problem when I worked on them. The engine made it 7 miles before dropping the intake seat. I have friends that own machine shops, and they have all seen it on the 821/823 heads also. Definitely makes you uneasy rebuilding these heads unless your replacing all the seats - which most customers won't pay for.

Most of the time, this failure is caused by overheating the casting. A common problem in a fresh build is not getting all the air out of the cooling system. The air pocket (s) create hot spots, localized, often in the heads. This can cause over expansion of the head. With as many of these that are out there, it is also possible that there was a machining error, lack of press on the seat insert, when GM, or whoever installed the OE seats. If, when, the engine gets a little unhappy, or is ran lean, or is overtimed, the seat can work itself loose. See it on the HEMI platforms too.

Any way you look at it, it is a sucka$$ problem to experience. That head is fixable with an oversize seat btw, The question would be if it is worth your time and effort.

 

Very true.

Irrelevant in this case though since that isn't what happened here.

 

Yeah…it’s been apart before. Someone did a down and dirty clean up job and sent it.

 

That's not minor at all. My guess is that that valve stuck open for some reason and the piston hit the valve. More than likely bent the valve and then they simply replaced the valve at some point.

 

From the picture in post #9 it's clear the intake valve did make contact with the piston and as a result could have led to the damage. Stating that the seat is perfectly fine is laughable to me but hey that seat may still be good to re-use but it looks to me like the valve seat is not seated in the cylinder head correctly or should I say starting to come apart from the head. I'm not one who's seen and worked on hundreds of cylinder heads in my days but I have several sets of stock LS heads that do not look like what's shown in OP's first post.

 

OK then: what's wrong with it?

I see a perfectly good seat, sitting perfectly uniformly in the head casting, with a perfectly good valve contact pattern. I see a clean straight line of contact between the bottom of the seat and the head casting, in the throat of the port where it bottoms out; no sign of any gap or any such thing down there. I see abuncha carbon and combustion whatnot all around it on the chamber side, as would be expected. I also see dents in the head casting next to it, where a valve hit it long ago. I see that the dents are not as deep as the edge of the seat, meaning, the seat was harder than the valve (musta been a crappy stock valve) and the valve didn't damage it, and it wasn't even replaced when the spring broke way back when and dropped the valve; since there was nothing wrong with it then either, it didn't have to be.

Yeah it's UGLY having all that damage around it; butt the seat itself is FINE. Which is not to say that I'd run it as-is, or that the OP should; only, that the OP's seat is firmly installed in the head right where and how it's supposed to be, and isn't A Problem in and of itself. There's nothing wrong with that seat. FAR different from the one in the photo in post #4, which HAS come out of the casting.

 

Do you not see where the seat has separated from the head from roughly 10:00-2:00 position?

 

No in fact I didn't... looks perfectly fine to me. All I see at that spot is abuncha built up carbon and combustion detritus on the chamber side of the seat.

Look down at the bottom where the seat is pressed in uniformly against the step machined in the casting. No gap there. Looks exactly the same all the way around.

The seat is fine. Nothing wrong with it. It's right where it belongs. It has nothing to do with the damage from the long-ago broken spring and dropped valve that hit the piston.

 

In fact, let's get straight to the facts.

OP, is the seat out of place in that head? Or is it correctly seated (hahaha) in the casting?

 

Well even if the seat is 100% in the right place it's still not something I'd want to bolt to an engine and run. For all we know you could fill the chambers with alcohol and shoot compressed air into the intake runner and it seals perfectly but then again maybe not and it manages to leak around the outside mating surface of the seat.