1999 Expy engine knock

1999 Expy engine knock..... Back together

So I go on a drive to N.J. from MA. Check all my fluid before I leave. Oil and Filter about 300 miles ago K&N filter with 5W 20. Drove all the way down 250 miles no issues (but the usual valve ping). All gauges reading good getting 10.3 mpg. Cruising between 50 ad 55 mph. Just as I get to my exit I hear something odd. I pull over engine idles rough has a knock. Gauges still fine no CEL.
Damage done I guess, drove off the highway to nearest hotel. Oil level good, filter not collapsed, no leaks, and antifreeze level all good. So I assume a spun bearing. Rented a trunk and trailer ad got it back home. It starts with no issue not even drag on it. Seems to be more of a top end knock than lower. Got a second opinion that person says the same thing as I do. Sound like knock or clatter?
Started disassembling the engine to pull the valve covers to see if the issue is under there. Way to much to get to them so basically started to break it down for a complete pull.
Looking to see anyone has any suggestion as to what to look for as I go. i'm going to look at the exhaust today I do not think its that though.

I would use a mechanics stethoscope and locate the tap before tearing into it...

Thanks for the reply. I went to continue taking it apart. What would have been process, what would I be listening for just for future reference if I the same issue later. Started taking apart the top end to see whats going on under the covers. Anything to look for? dose this engine have those butterfly baffles? I have seen that this could be an issue.

History:
The engine was rebuilt has about 30K on it now.
Had to replace (plastic belt tensioner). Warranty
No start issues, Quarter Sized hole blown through Plenum. (2013)
Fine since

When there isn't anything wrong with an engine it will have "normal" operating sounds. You will be able to hear them through the stethoscope and not notice anything standing out. When there is something wrong you cannot miss it since the difference in sound is so apparent.
You can use the scope anywhere on the engine being careful where you place it - avoid the fan blades, serp belt etc. Don't slap it on the engine the sound amplification is very high.

Make sure the oilers in each head are not obstructed.

Thanks for the info I'll look at those. What would they effect top or bottom or both?
Hoping its something simple up top.
Worst case not sure which way to go with this. Finances is one issue, but need it fixed. Debate is replace or rebuild again as this engine was (supposed to be) rebuilt once. Cost of used engines with 100K is over $1000.00 or more, even saw one with 253K on it. Rebuild kits depend on what gets replaced $386 to $700. Make no sense to buy used if new parts are the same cost. Then machining and using old connecting rods if able.
Any idea what the machining would average?
* Guessing on boring the cylinders
$500.00
* The crank if scored.
$200.00
* The Rods if scored.
With crank
* I know I'm missing something else.
Heads $400 labor plus parts
Got any ideas what should be or recommend to do here?
Have you pulled one of these? Any tips?
Did you pull the nose, does it need to? Any where i can get info on this?

You don't know the cost of a rebuild until you have the engine apart and are able to measure the parts & clearances between them.
Oilers are for the top end.
If time is a problem crate engines are the way to go. The engine can come out through the top with the hood off. More can be had by pulling the radiator out also.

So this is where I'm at today. Pulled throttle body, intake, plenum, fuel rails, injectors, coil packs, harnesses, hoses, right valve cover.

This #6

Have not pulled the left valve cover I'm assuming that it may have the same issue.

What do you think about this?
Could this be my noise?
Hammering up and down the stem?

Well...you have a problem with that head. Part of the guide is missing (which is obvious). It probably is still in the cylinder beating the hell out of everything or it is in small pieces in there - beating the hell out of everything.

Couple choices at this point:
1) Borescope to view the cylinder/piston checking for damage
2) Pull the head to inspect the cylinder/piston
3) Price a rebuild
4) Price another engine
5) Price reman heads and gasket set if the internals are ok from #1 or #2 above
6) Get sheet faced and worry about it later

The guide looks the same size as the other seven. Looks like it broke slid down and is probably hammering back and forth. I think it may be the same for a couple of exhaust valves too. Unless that one is echoing in the engine.

Do not have Borescope to view the cylinder/piston to check for additional damage. Hope the plugs come out they only got 30K on them. I'll see if I can rent one or I'll have to just pull the head to inspect the cylinder/piston myself. Rebuilt engines range between $1850 to $3000. Re-manufactured heads $600 and gasket set is $150 all on eBay. Don't drink that much now this happened LOL. Not sure if I would save any money rebuilding myself. But I would definitely know it was actually done 100%

Still need to check the timing components.

Think I'm better off coring / exchanging the heads for reman?
Any tips on the head removals?
Any tip on what to look for behind the timing cover?
Dumb Question, besides pulling the pan is there a way to check the rod bearings?

Thanks

See if the other head has the same "issue" with the top of the guide. It may look like a problem but not be. What are the chances all or half of them are missing some material?
I would wait before pulling the head off.
Timing chains - look for missing guide pieces. Drop oil pan to retrieve them or oil pickup will clog.
Rod bearings - drop pan and pull rod caps is the only way to check clearance