Burnt valve..now bad piston

Originally had a miss on cyc 1 and P300 and P301 check engine codes on my 96' Jeep Cherokee 4.0 Compression test showed 40-45PSI on number 1, and 130-155 psi on the rest of the cyclinders. Put a dab of oil in number one and rechecked, went up 5 psi. Moved on to the leak down test, and constantly had air blowing out the intake. Yes I am sure it was TDC, and still had air coming out the intake. So i determined it had a intake valve issue. Took the valve cover off, and removed the rocker arms for cylinder number one, to ensure both valves would be fully closed. Did another leak down test, and still had air coming out of the intake. It wouldnt even hold enough air to put a percentage on it, so 100% loss. Well I got the head off this evening, and of course piston number 1 has an issue. The rest look normal, and even the head gasket looked fine. The engine has 240k miles on it, and ran like a champ besides a obvious miss at idle and check engine code. The original plan was to have a valve job and throw it back together. Yes I know the increased compression might blow out the rings on the existing pistons, but I was willing to chance it. Does it piston look bad enough warrant a rebuild / replacement? I cant figure out what would cause just the edge to chew up instead of the center. The combustion chamber looked fine, never had a spark plug issue on the cylinder either. Let me know what you guys think? Oh and I forget to include, the cylinder walls on not scratched or scarred.

:flame:

Heck you've gone this far, pull the piston out and have a look. Old school is if it ain't broke don't fix it, nothing wrong with re ringing one cylinder (old school). I would look for any vacuum (leak) issues near the front of the intake and maybe replace that injector. Usually when something burns like that, it is from too much air or not enough fuel. There is bound to be some splatter on the top ring IMO.

Well my current options are go with a used complete motor for $200-300 with 150k-200k miles on it (with the "craigslist promise" that it runs correctly)...But a guy local to me has a *brand new* 0630 casting head that includeds springs and valves for around $200. I was quoted $150 to check my old head and do a valve job. I think im going to go get the new head, set it on there and do a compression check. If all the numbers look good, put it back together. If not I'll hone all the cylinders, replace that one piston, throw new rings and bottom end bearings in it..and then sew it back up. Cost is of course a factor, but doing this job more than once anytime soon is also a factor.

Is the valve seat toast? Or is it just the valve?

Now that is beyond my knowledge. From my eyeball inspection, the valve looked the same as the rest of them. And the valve and spring seemed to be going up as high as the rest of them with the rockers off. I can go take some pics of the head and post em, but honestly I dont know.

You can usually see a bad valve, the edges are melted or the top looks a bit concave ( slightly bowl shaped) or it gets stuck in the guide.
Turn the head upside down, put it on some wood blocks and level it a bit. Fill the combustion chamber with water, see where it leaks out, in the exhaust or intake port.
Take it to a shop and have them remove the spring and valve for that cylinder. See how loose the guide is, how damaged the seat is. It might be as simple as a piece of junk stuck onto the valve or seat. I had a piece of gasket stuck in there once.
It's usually the exhaust valve that screws up, rarely the intake, except for the one reason why I'm not a a fan of dumping any "cure all in a bottle" down the intake, no telling what you might flush between the valve and the seat that just might stick and stay there.
If the valves appear to be OK and even if they aren't I'd be curious to what the compression ring looks like on that piston. And be wondering what caused the problem in the first place.

Going to try the "water" test here in a bit, we'll see what happens. I'm curious as to what caused the piston damage as well. I dont want to just fix the piston, and not fixed what caused it. Does it look like heat damage or foreign object damage? Im wondering if the injector is partially clogged and causing that cylinder to run lean, which made it heat up. Or if it was some type of physical object in there causing the damage. But I think there would be more marks..like scaring on the piston wall, or even on the valves or combustion chamber.

I was kinda leaning towards getting that brand new head, and bolting it on and checking the compression on the number 1 cylinder.

I sure can't say for certain, could be an injector. That can also happen if you are getting too much air to the cylinder, intake gasket leak or maybe even a vacuum line connection. I always wondered about the vacuum connections on one end of the intake or the other, if they leaked they had to have some affect on the air fuel ratio. Maybe enough to do some damage. I do know a vacuum leak at one end of the intake, be it a gasket leak or a vacuum connection, will sure enough make for a rough idle.
Crispy pistons and exhaust valves were pretty common on carbureted motors in the front cylinders. Acceleration tended to run more fuel to the rear of the motor than the front. Should be a non issue in MPI motors, if the injectors are OK.
Lay something flat on top of the valves and see if you can see more concave bow in the top of the cylinder one valves, relative to the others. Valves can bow and get lightly concave and not seal right, happens sometimes with a head gasket leak and coolant into the cylinder. You can also measure the rocker height at the valve end relative to the others, if the valve has a bow and is dished more, the rocker end is higher.
I was looking at the head gasket *metal ring* seal mark on that cylinder in your photo. Looks like a gap in the gasket seal very near the scorched spot on that cylinder. There is usually a shiny circle on the block deck where the metal ring in the gasket seals the cylinder? Is it possible you were loosing compression through the head gasket ring seal?

8Mud,
You are the man for the water test. I got the intakes off the head, and started looking at it. The intake valve does have a small place in it where it looks to not be sealing. I tried the water test, and sure enough the water leaked thru the intake valve and out of the head. I snapped a few more pics of head gasket, i think you may be right and the gasket may have been blown right at the front. Guess I am going to go get the new head and head gasket set. Put that on and run a compression check. Should I try the water trick on the piston in question to see if it holds? I can use a shop vac to suck it back out before it rusts. I hate to get this back together and waste a head gasket and set of bolts, only to find out I still have low compression on #1. But at the same time I really dont want to pull the pan and piston. Heres some pics, let me know what you think. Oh yea, is it normal for your intake runner to be so gunked up?

Is that a notch burnt on that valve or is it some sort of mechanical damage? Looks like a ding/dent or a small bend to me.
Filling water on top of the piston won't tell you much, it will leak down between the ring gaps and may wash junk between the rings.
The rings are supposed to be somewhat mobile, though I have seen some rings jammed in the ring slots pretty good. I've seen pistons with more scorch than yours with material kind if welded to the compression ring, which can't be good.
I really don't know if that burnt spot on the piston will be an issue or not. My eyeball tells me it exceeds the maximum allowable tolerance though:laugh:.
I once ran a bent valve for a long ways and the seat was still good. A couple of hours after I had the head off, I had a new valve in there and lapped.
Guess it depends on the valve guide if it is worth it or not to salvage the head you have.
The intakes mostly look like that, though yours does seem worse than usual. Do you have any serious blowby issues with your motor? Your compression seems good except for number one.

The new head is a done deal, pick it up tomorrow at 2pm. Came from this place http://cylinder-heads.com/ What would happen if i dont replace the piston? I intend to bold down the head, and then do a leak down test. If I have good compression, what could happen with the piston?

I would replace the piston, but then I would end up replacing ALL the rings on al the pistons, and all the bearings in the bottom end. And by then, I might as well pull the block and get it machined instead of half assing the rebuild.

So If I have good compression with the new head, what could happen with this piston?

The valve on the old head, looks to be bent from physical damage.