[boboli]

I haven't driven my tbird in 6 months. Last time I drove it, I stopped at a few places,  I then left a light, calmly,  and instantly it developed a terrible knocking sound. Like a rod knock. The engine sounded terrible but nothing else sounded or showed wrong. A friend helped trailer me home and I left it parked till I had time to take the head off, expecting the worst
Finally had time to pull the head today and I find this pancake flat piece of metal. I think in cylinder 3 but it could have been 2. At first I thought it was a nut that was smashed flat. But it's actually aluminum. I'm hoping that it being a softer metal, it hasn't done any real damage to the engine. I plan to do a few upgrades while the head is off, but otherwise I'm hoping just a new head gasket, some other gaskets, and new bolts,  I'll be back in business.
I'm thinking about having the head checked, just to make sure the valve isn't bent and everything is alright. Again it's off, so no better time to have it looked at!! 
Any idea where this could have come from? I can't think of anything aluminum that would have been in my intake tract. No work had been done on the car in awhile. So it's not like I left something in it to be sucked through. I also don't let any one else work on it.
Thanks for advice and guesses on what this is. I'll keep searching and hopefully find the cause!

https://photos.app.goo.gl/rScG7PmSWBY5uPEY8

https://photos.app.goo.gl/CtcanDE5gSdpTK7L6

[evintho]

It almost looks like a smashed dime! Exactly where did you find it? Sitting on top of the piston? If so, check the piston closely for chunks missing, especially on the top edges. Rotate the crank so the piston slides up and down the bore and check closely for cylinder scoring, the entire length of the bore.
Definitely have the head checked and with 162K on it, now is the optimum time to have the head completely gone through.

[Racingjake]

I would start at the air filter first and work back to the cylinder. Could be a casting part from the intake system or turbo ?

[Howard]

Not saying it IS, but if you have a FMIC, it could be aluminum slag from inside the pipe/ tank welding that finally broke free.

[TurboRay]

.
It's hard to imagine how such a chunk could've been repeatedly hammered between the quench area of yer head and the top of a piston w/o leaving noticeable/obvious divots &/or marks, boboli. IOW......you should easily  be able to determine which hole it was in. As for its origin........lemme get out my crystal ball, since it's totally unrecognizable, lol.

Personally, I think you might wind up regretting it if you don't push out the damaged piston(s) and determine if the top ring land has been crushed/bent to the extent of clamping the top compression ring(s). At the very least, you should put the suspect piston(s) at TDC and make sure it/they still move radially in all directions.  <shrug>

[boboli]

I had a bit of time to look at it again, after reading your comments!!
First, the car has the stock intercooler. So unlikely slag from an aftermarket one.
But after rays and evintho posts, I looked and the cylinder that all this happened was obviously 3. I thought I took a picture of the piston and there was a obvious place were something either hit the piston and damaged it. Or, and I think less likely, something came off the piston and banged around.
I don't seem to have that piston pic, So here's the bottom of the head. Obvious mark where the piece was hitting

https://photos.app.goo.gl/ns2KMEdu2CEmmZe67
The top of the piston had a similar mark but looked a bit more hammered. I don't think it was so bad, that aluminum from the piston came off. More likely, just impact damage.
But then I looked at the exhaust manifold. And cylinder 3, the problem one. Is the only white colored one. Plus it's got globs of melted aluminum right at the entrance to the exhaust.
https://photos.app.goo.gl/wXp4uyV4jtGjFmsV8

Here's a shot of all the exhaust ports and the one with issues and the aluminum piece is number 3. But the cleanest! So maybe there's another issue

https://photos.app.goo.gl/LY8KNyDkL3Kcn2ox5 

since I trust your judgment Ray, but I wish your crystal ball worked better, 🤣
I think I may just need to pull everything and look at it all. The motor leaks a lot from a lot of places. And when I got it, I decided to replace the clutch with a squeaking t/ o bearing!! It's been a decade of riding the clutch. So maybe it's time to just take care of it all!!
Please let me know what you think of these pics 
Thanks

[TurboRay]

.
Whenever one of the exhaust or manifold ports exhibits a drastically lighter (non-carboned) appearance than the others......it's almost always caused by either a very lean mixture or the intrusion of water/coolant into the combustion process, Matt. And, based on the aluminum "mini-marbles" deposited in the mouth of that #3 manifold runner......I'll choose lean mix over water intrusion.

Therefore I suggest (1) Having your injectors flow-checked/balanced by a reputable injector-service like RC Engineering, FiveoMotorsport, etc.. ~ and, (2) Checking the perimeter of that #3 piston VERY carefully for rough/melted edges. After re-examining the pic of that "chunk" that you found......I'm leaning towards a compacted group of those "mini-marbles" (like those seen in the runner of yer exhaust manifold) that suddenly became "unstuck" from the non-quench area of yer head or piston dish........rather than a single chunk of metal. 

Obviously, this ghetto/"dartboard" autopsy can't be very precise w/o the input of other more-specific data, BUT.......that's my story (for now) and I'm stickin' to it, lol. <shrug>

[boboli]

Thanks Ray!
I agree that lighter color means that cylinder was probably lean!!
When I took the head off about 20k and about a decade ago, I took the injectors to a local place that rebuilds and flows them. But that doesn't mean something hasn't gone wrong since. Or if they did a good job!
The car has been pinging any time I get on it. So maybe a lean cylinder 3 is the reason
I will try to get a pic of the piston top. I don't think what damage I see on the piston top, means the piston was melting. To me, it looks like contact damage. Plus, the piece I showed earlier, looks to be more material, then what could be missing from the piston top
But I could be wrong
Hopefully the engine is salvageable!!
I'd hate to see the car go from my dd to another fox rotting in my yard!!
And I don't want to sell it. Tbird still don't seem to get the love, that basically all other 80s foxes, and even any 80s Fords now get!

[TurboRay]

.
LOL......"Fox rotting"   

[Racingjake]

Too many Mustangs LOL, that's why I got a 65 Falcon and 87 Turbo Coupe. I read an article about the 2,3 Turbo in the early 90's and always wanted one. I don't pay much attention until I see a Falcon or Turbo Coupe then I'm a rubber neck.