I have a pulled 5VZFE out of 2000 4Runner that had a stuck valve in cylinder # 5. The engine spins easily and there's no mechanical issues with the pistons/cylinders/block/crankshaft that I can see. I compression tested the engine and here's what I got:

1- 200
2- 174
3-200
4- 174
5- 0 (stuck valve)
6- 128
I got the right head off and the stuck valve went right back in with a light tap from a rubber mallet. I know compression spec is 200 with +/- 15 PSI and minimum is 180. I would guess it might be a similar issue with cylinder #6 All things considered the cylinders on the right bank look real clean and still have good cross hatching. What would have caused the stuck valve? If it's something minor I might just redo the heads and compression test again instead of tearing it down any further. If you need to do a visual inspection let me know and I'll add photos. Thanks in advance.

That's a lot of work to go through without having the heads redone. I'd pull the other head off as well and send them to a competent machine shop to tear them down and give them a good examination before rebuilding them. These heads are know to develop cracks between the valves and they are easy to miss if you're not looking close enough.

I agree with Tim. At this point just get both heads rebuilt and resurfaced and call it a day. Lots of things can cause a stuck valve, but none of them are permanently fixed by tapping the lifter back with a mallet.

I would get both heads redone since #6 is out of spec. Like you said, no point in stopping with one head if I'm that far. The engine is on a stand so it's not an immediate need. We'll see what the left bank looks like when I get the other head off and if it's worth saving.

It's a spare engine I grabbed for spare parts and a last resort if my 4Runner's engine decided to go out, but now it's looking like more than I bargained for. It might have to be a longer term project if it's going to cost more in repairs than what I paid for the engine. Maybe used heads would be a cheaper option, but so was this engine and now it's just a heavy paperweight. Lots to digest, but thank you for the input.

When you pull that other head expect the unexpected. Hopefully low compression on 6 is head related.


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UPDATE:

We got the other head off and things look okay. The piston heads are pretty black with none of them showing a coolant issue or head issue. The amount of carbon buildup in the combustion chamber and on the valves is pretty bad. We decided to drop the pan and that's when I found what could only be described as chunky black pudding. I don't think this engine had an actual oil change within 15k. I'm definitely now leaning towards scrapping the engine since I have no idea how long it ran with the sludge. I could be wrong, but I'd rather not get too invested into a $500 engine. I don't know, convince me otherwise.

I would also scrap the engine in your situation. If you are decent with a welder you could turn it into a coffee table or something along those lines. It's on my long list of things to do lol

How are the cam bearing surfaces? Smooth or scratched? You still see the crosshatch pattern in the cylinders using a flashlight?

Now that you are there, it would be pretty easy to look at a few conrod bearings and matching crank's surface. Would give some idea on the engine condition.

Since it's out of the truck, it would not be a long nor expensive job to slap new rock auto bearings set in there if the crank still looks fine.

Sludge isn't a death sentence. These engines have been known to run on 1 quart of oil. Clean it up, check the bearings like mentioned and clean up the heads if you plan on dropping the engine in. If you are not and just keeping as a spare, then it's up to you. Storing an engine for years is a tricky thing and will only make things worse.

If I do keep it, it would be used as a core. I talked to Yota1 about them wanting it and sent them pictures. They said I'm more than 2 hours away from the nearest freight shipper (I'm in the middle of BFE) so they would pass. Otherwise, they were definitely interested in taking the engine. This leads me to believe that it's not that terrible of an engine. I found the VIN plate and this thing definitely didn't have 116k. It was out of a 2000 with 220k on the last reported mileage. What can I say? I got hosed.