[Mountain Escape]

My son actively cranked the engine with the key in start, clutch pressed, and wide-open throttle. The needle didn't budge.

I was guessing you wouldn't get compression in the cylinder with the oil in it, but I am surprised you have got zero compression in all four cylinders…
That leads me to think Dwight is in the right Neighborhood with the topend - valves/camshafts/timing chain

It's weird it happened overnight.
Did you hear it running the night before? I am just wondering if it had developed a misfire or a knock before it was turned off. Maybe ask your daughter if it dieseled on after the ignition was cut... anything acted or sounded different.
Sometimes you have to ask the right question… It was running, but how well? ( : with an oil soaked spark plug, it had to have a healthy misfire

I wonder if it could be something 'simple' like a cam/crank position sensor(s) for your no start issue? I don't know if you can electrically test one. I think you got two camshaft sensors because of the DOHC. They are at least not expensive. I think you have to remove the timing cover to get to one though

Maybe you were lucky, in that it made you find the oil in the cylinder… before the engine blew up.
try to look for the silver lining! ( :

 

[dwightbresemann]

Do you have access to an air compressor? If you do, pickup a leak down detector from Harbor Freight Tools – Quality Tools at Discount Prices Since 1977.

Has anyone recently worked on this engine. There is no key way to hold the lower chain sprocket to the crankshaft. It is the clamping force of the crankshaft bolt with a special diamond laced washer to lock everything together. This never fails unless touched.

The 2.3L timing chains almost never fails. Even if it jumped a tooth or 2, you would still have compression. To lose compression on all 4 cylinders is weird.

It would be a good idea to check the chain timing first before going forward. Plenty of YouTube videos showing you how. A simple bar for the camshafts and use your scope camera to look in the block bolt hole for aliment of the crankshaft.

 

[Mountain Escape]

You know,
I remember my grandfather one time pouring a couple of ounces of oil into the cylinders of the tractor, then we came back the next morning to make sure that the oil was still there…
That is the hillbilly way to let you know if the rings are bad. ( :

just cause I was curious, I google searched, it seemed the main consensus for lack of compression in all cylinders is either a cracked head, or a cracked block.

 

[dwightbresemann]

You know,
I remember my grandfather one time pouring a couple of ounces of oil into the cylinders of the tractor, then we came back the next morning to make sure that the oil was still there…
That is the hillbilly way to let you know if the rings are bad. ( :

just cause I was curious, I google searched, it seemed the main consensus for lack of compression in all cylinders is either a cracked head, or a cracked block.

It would big crack to take out all four cylinders. If the poster indeed has no compression on all 4, it is a valve timing issue. Camshaft and crankshaft sprockets are friction fit by the stretch to yield bolts, no key-ways at all.

 

[Charles]

Welcome to the City!! Glad you joined us!!! I can tell you have great advice already.