N62 compression test question

[Fatcat]

Hello, I want to do a compression test on my car but Ive heard stuff about Valvetronic varying the result on the actual psi reading, can someone tell me if this is true and how this happens?

[BimmerBreaker]

Valvetronic limits the amount of air that can get into the cylinder, the same way as a throttle body being closed. Pressing the accelerator pedal will not force Valvetronic to increase lift.

The numbers may seem lower than other engines with the same compression ratio, but ultimately the more important thing here is the variance between cylinders. Compression test all cylinders and if one is drastically lower than the rest, it signifies a problem.

[aureliusmax]

your valvetronic actuators will set to the same position when cranking over the car so it's not going to implement any real variance.

all you need to do is warm up the car, remove all spark plugs, release both bank fuel injector connectors (1 each side located on top valve cover cable tray). and crank each cylinder until the compression gauge stops (usually 5 compression strokes)

[Fatcat]

Originally Posted by BimmerBreaker

Valvetronic limits the amount of air that can get into the cylinder, the same way as a throttle body being closed. Pressing the accelerator pedal will not force Valvetronic to increase lift.

The numbers may seem lower than other engines with the same compression ratio, but ultimately the more important thing here is the variance between cylinders. Compression test all cylinders and if one is drastically lower than the rest, it signifies a problem.

that makes so much sense thank you

[Fatcat]

Originally Posted by aureliusmax

your valvetronic actuators will set to the same position when cranking over the car so it's not going to implement any real variance.

all you need to do is warm up the car, remove all spark plugs, release both bank fuel injector connectors (1 each side located on top valve cover cable tray). and crank each cylinder until the compression gauge stops (usually 5 compression strokes)

sounds pretty simple, thank you

[Bmwe5320023.0]

Well sorry to revive and old thread but what results did you get?
I took my engine (N62B48) apart and did a bunch of things, replaced everything I could, did valve stem seals, timing chain, guides etc. Now can't seem to start my engine. Checked a couple of cylinders for compression, they're both at 100psi. So I'm not sure if something is messed up or if that's normal due to valvetronics?

[Fatcat]

Originally Posted by Bmwe5320023.0

Well sorry to revive and old thread but what results did you get?
I took my engine (N62B48) apart and did a bunch of things, replaced everything I could, did valve stem seals, timing chain, guides etc. Now can't seem to start my engine. Checked a couple of cylinders for compression, they're both at 100psi. So I'm not sure if something is messed up or if that's normal due to valvetronics?

Hello, if im not mistaken im pretty sure I got like 120psi, you should look out for variance instead mentioned by some of the people under this thread. My problem was that one of the valves in cylinder two wasn't sealing properly. What do you mean you can't start your engine? Does it just crank away?

[X5chemist]

Is stock compression more than 10:1?

[Bmwe5320023.0]

Yeah the engine cranks.

I'm not sure what's going on. I timed it well, but something is wrong...

1-8 are cylinder numbers

With valvetronic motors installed:
1. 20 psi
2. 85 psi
3. 20 psi
4. 85 psi
5. 100 psi
6. 95 psi
7. 90 psi
8. 105 psi

With valvetronic motors removed:

1. 30 psi
2. 85 psi
3. 25 psi
4. 95 psi
5. 120 psi
6. 155 psi
7. 145 psi
8. 90 psi

[Fatcat]

Originally Posted by Bmwe5320023.0

Yeah the engine cranks.

I'm not sure what's going on. I timed it well, but something is wrong...

1-8 are cylinder numbers

With valvetronic motors installed:
1. 20 psi
2. 85 psi
3. 20 psi
4. 85 psi
5. 100 psi
6. 95 psi
7. 90 psi
8. 105 psi

With valvetronic motors removed:

1. 30 psi
2. 85 psi
3. 25 psi
4. 95 psi
5. 120 psi
6. 155 psi
7. 145 psi
8. 90 psi

oof, those psi values vary a lot. Have you done a leak down test to find out where it's leaking from?