Used Engine Leak Down Testing

Hey everyone. I am currently replacing the engine for a 2013 Range Rover Sport 5.0L (severe rod knock) and I’m having some trouble while testing the replacement engine. I have now received 2 used engines but both engines are not passing a leak down test. On both engines, I’m seeing as much as 70% loss on multiple cylinders and as little as 5% loss on other cylinders. I am positive that I’m testing everything at top dead center of the compression stroke and even have the valve covers removed to ensure the camshaft lobes are not beginning to open the valves. Despite this, I can hear, see, and feel air rushing past the intake valves when they should be fully closed. While keeping all of my variables exactly the same, I ran the leak down test on the original engine (the one being replaced) and I only see about 5% loss.

Seeing such poor leak down results on back to back replacement engines seems very suspicious to me. I’m wondering, what could I be doing wrong with my leak down test? Is this a normal result for a used engine? Is carbon buildup on the backs of the valves preventing a good seal? Would simply installing the engine and running it solve the leaking valve issues? Should I keep testing used engines until I find one that passes a leak down test?

Normally for used engine, a simple compression test (which is dynamic and more closely simulates a running engine) is what you perform when the engine isn't installed (assuming you can mount a starter, and connect a battery). You can check to see that compression is "in the range" and close to even for all cylinders.

A leak-down test really needs to be performed with warmed engine to simulate the running conditions with a static test. But running it when cold can allow better diagnostic of where the leaks are occurring (intake valves, exhaust valves, or rings). Did you check the cylinders in the firing order?

Did you adjust the intake valves? Or did you measure the clearance? Are you sure you are at TDC compression, and not exhaust/intake overlap? If you can't get a feeler gauge to check the clearance that may be the reason, or there could simply be debris (like carbon dislodged from the combustion chamber when the engine was removed / shipped) on the valve seats preventing them from closing. The valve clearance would clue you in if this was happening.

Good luck with your search!

Thanks for the reply!

I have not performed a compression test on the engine yet simply because of the need to run a starter on it but I will look into a way to make that happen.

While performing my leak down test, I tested each cylinder in numerical order based on their identification. I was able to do this by simply watching for the compression stroke to come up after the intake cam lobe opens and then closes the valves. I then used a screwdriver in the cylinder to watch as the piston reached the top of its travel on that compression stroke. I tested each cylinder at that point and got my failed test results. Also, I performed that same process on an identical engine at the exact same temperature and saw a passing test result on the leak down (5% loss). This leads me to believe that the testing procedure and equipment are not flawed and the low temperature of the engine shouldn't matter very much.

Unfortunately, there is no valve adjustments to be made or clearance measurements to be had on the intake side as the lifters are hydraulic and self-adjustable. That's why I was watching each cam lobe with the corresponding cylinder being tested, to make sure none of the valve were being lifted. Out of curiosity, I even applied pressure to the failing cylinder and then rotated the engine two full rotations and the maximum pressure reading in the cylinder never increased past the reading I was getting at my perceived TDC on the compression stroke.

There is definitely carbon on the backs of the intake valves (typical direct injection gunk) but it's certainly not excessive. I did try to blow off the valves with compressed air but it didn't make a difference in the test results. I would think if any debris fell into the intake ports it would just sit on the back of the valve and not interfere with the seat since almost all of the intake valves were fully closed during removal and shipping. If the poor seal is being caused by dirty valve seats, I don't have a good way of cleaning the seats without removing the heads and cleaning or even grinding each individual valve.

Maybe I'm just overthinking it and simply running the engine will solve all of my problems. I would just hate to replace this engine twice!