Ever since the rebuild, I have had an engine knock that is kind of a rattle at startup and is a more consistent knocking noise once warm. Between startup and warm i don't really hear anything unless I go under the car. I have the engine apart with the oil pan, lifters and timing cover off. When rotating the engine without the valve-train (lifters, pushrods, rockerarms), I head hissing noises. I went to harbor freight and got a leakdown tester. I tested at 90 psi and made sure the pistons were at tdc by looking at them from below.

Here are the results.
Cyl 1: 1%
Cyl 2: 3%
Cyl 3: 16%
Cyl 4: 20%
Cyl 5: 29%
Cyl 6: 23%
Cyl 7: 7%
Cyl 8: 9%

I know the test is supposed to be done when the engine is hot, but since the engine is apart, it is cold. How terrible are these values? Are they just bad because it is cold, or do I have issues? I put some oil in cylinder 5 and it reduced the leak from 29% to 13% indicating a ring sealing issue. The hissing noise also seems to come from below the pistons. I don't have any oil consumption issues or smoke out of the exhaust.

Could this be related to my knocking noise and metal particles in the oil? The knocking noise happens once per camshaft revolution. 1/2 the crank revolution. The metal particles are so fine that the oil filter does not catch them. I did get an oil analysis and got these results. Note that aluminum, iron and chromium were high. This oil sample was 3000 since the rebuild and the second oil change. Currently it is 6k miles since rebuild.


What should I do to fix this? Do I need new pistons, new rings? (I already replaced rings) I did not hone the cylinder liners as per the rave and this forum's advice. Did that cause these issues? I'm going to pull a good and bad piston to see how they compare.

 

Since no oil consumption or smoke, don't panic. Cold engines just don't seal up as well. The hissing is compressed air escaping, probably pushed the oil out past the rings, and oil is what creates the ultimate seal. It can be difficult to get consistent results with the HF testers.

Do you hear any hiss at the intake valves or tail pipe during the leak-down tests? Valves are also probably not perfect. Use a section of hose held up to an ear to isolate the noise.

Exhaust leaks happen at the camshaft frequency and can cause ticking sounds that change with temperature. I had one new rocker arm out of a whole set with a loose bearing cup that caused ticking (also at camshaft frequency) that changed with temperature/oil viscosity. Found it by using a mechanics stethoscope and running the engine with a valve cover removed. Maybe not so easy on the Thor engines.

High metals in the OA could just be from break-in, should decrease for the next check. The trend is what is important. The Motor Oil Geek suggests first oil change during break-in around 500 miles due to high initial metals. Try not to sweat the small stuff, these engines are work horses, not Formula 1. Easy for me to say, but it's your truck in the end.

 

How is the power? Fine? If it’s down on power.. I’d figure it out ... if it’s not down on power, I’d just keep trucking but... perhaps best course of action might be:

Change the oil, drive 1000-2000 miles in city driving conditions. If still bad results / particles, you then have more of a baseline that you have an issue. Then you can decide what to do. I don’t know if your current findings so recently after a rebuild are in and of themselves, conclusive.

Although the noise and the hissing is I would agree somewhat suspect. FWIW, I’ve driven Discos (4.0 and 4.6) with knocking noises for literally 20,000, 30,000, 40,000, 50,000 miles. Forever basically. I agree with the comment above about these not being precision “F1” motors haha. I had a 2003 that I drove with a deeply concerning engine knocking noise for basically the entire time I owned it. Years.

I don’t know about this hissing tho...

 

The fact that you have some cylinders with almost no leakdown and some with significant leakdown is concerning. The question is where. Your oil in the cylinder test proves some is past the rings, but not all. You should be able to hear where the air is escaping - crankcase, throttlebody, or exhaust pipe (rings, intake valves, exhaust valves). Were you able to determine if the knocking was left side or right side? Sometimes you can detect which cylinder it is by disconnecting the spark plug wire for each cylinder one by one until it gets quiet. Also check all the rockers for looseness. The knock being once per cam rev suggest valvetrain, mighht be a collapsed lifter.