xDrive40e - Engine knocking noise

[Baxy]

Hey guys, I'm from Cluj, Romania and in February this year I bought a 2016 xDrive40e and realized that if the car sits a lot, like more than 2-3 days (due to the pandemic wasn't using it much), at cold starts it was blowing white oil smoke. Researched a bit on that and discovered that the N20 engine has an issue with the oil feed line to the turbo. The fix is to replace that oil line with a revised one that has a built in check valve. When changed the oil feed line the entire turbo has been removed and when fitted back again a kit for turbo replacement parts like gaskets and o-rings was used.

More details about the problem here: https://bmwtechnician.com/2016/05/13...d-line-update/

The smoke issue is currently fixed, but after getting the car out from the auto-shop and inspecting the engine bay, I was hearing a knocking noise, that I don't recall hearing it before. The guys from the shop inspected all the parts they were touching to be sure everything is put back in place and tried to identify the noise, but they are not sure from where it may come from.

The final conclusion was that is some sort of a valve that's hearing and it's normal.

Another thing to mention is that if I put the car in Sport the noise it's still there but barely noticeable. When putting back in Comfort or EcoPro the sound is back again.

To be honest I don't think it's normal and I'm trying to see if anybody has heard such a knocking in the engine bay that is comparable with what I was recording in this YouTube video:

Any help is appreciated.

[SMC23]

What is the production date of your car?

I havent heard about this issue before but will check my engine.

[turboawd]

Does the sound increase with the engine speed? Remove the oil cap while it's running to see if the noise changes. Though you might get a code for doing that.

[Baxy]

scanido The production date of the car is 02/2016.

turboawd If I rev the engine it only increases the frequency of the knockings, the sound seems the same. If I remove the oil cap the sound is still there. The car has no fault codes, runs perfect, no changes in power.

[chumbedi]

Check oil level and inform

[Baxy]

chumbedi Oil level is at max.

[corduroy]

I'll take a look at mine with the hood up. The N20 is pretty loud, especially at start. Has a kind of diesel sound due to the direct injection. Does it get any quieter when the engine warms up?

[Baxy]

Actually the knocking is noticeable when the engine is warm. When cold started it's not present. Forgot to mention that.

[turboawd]

Use a piece of hose. Put one end to ear and other end around engine. Use as a stethoscope.

[corduroy]

I can't tell through the video, but is the knocking sound similar to:

?

Guy there said it was a knocking rod. Usually a knocking rod gets worse as the engine warms up... I hope that's not the case here for you!

[skoold2003]

Originally Posted by Baxy

Actually the knocking is noticeable when the engine is warm. When cold started it's not present. Forgot to mention that.

This sounds really similar to the symptoms when I had my bearing going bad. Only did it while warm and increases when RPM increases. You should bring it to a shop ASAP and they can check for metal shavings in the oil.

[Sebastian21]

Hi there. Im from cluj to . Sounds you have 2 type of noise there , 1 metalic wich can it be from chain and 1 very deep wich i have same on my 2011 x6 and i cant figure out what it is . I look on my oil level it is at max but when i start the engine and chek on dash board the oil it seamse its to much , so if you have like me full take out 300 ml and see if works for that deep sound . For the metalic sound when whas the chain change ?

[-c-]

Originally Posted by Sebastian21

Hi there. Im from cluj to . Sounds you have 2 type of noise there , 1 metalic wich can it be from chain and 1 very deep wich i have same on my 2011 x6 and i cant figure out what it is . I look on my oil level it is at max but when i start the engine and chek on dash board the oil it seamse its to much , so if you have like me full take out 300 ml and see if works for that deep sound . For the metalic sound when whas the chain change ?

Just to chime in I had my 2016 engine replaced by bmw good will because their was scoring on the cylinder wall and I guess their was a small batch of engines that where bad on the early builds. Even though I was over 50k they replaced it. Sounds like the 4 cylinders have some issues.

[ProjektAutoScott]

To add some resolution to this thread:

UPDATE 04/26/2024: see part B, which is a much larger issue.

I am revising this post as a result of new findings.

I recently tried to diagnose a 2018 40e with 70,000 miles. The knocking/thumping sound was identical to the video above. Very in sync with RPM, very similar to rod knock or wrist pin knock sound. I was certain at multiple points along the way that the car had some sort of internal knock. This knock was resonating through the entire engine, into the cabin.

In this case, the sound was most noticeable when the vehicle had warmed up, after the cold-start high idle and open waste-gate cycle. The sound seemed as if it were coming from the exhaust side of the engine, and at times seemed like it could be at the rear or front of the engine. Hard to pin-point, even with a scope or chassis ears. More prominent around 1500 RPM, even had a nice scary death rattle when the engine was decelerating from a rev in neutral. Again, just like engine knock.

Here is the sound from inside the cabin. Engine bay sounds exactly as the post above if you need reference https://youtube.com/shorts/X1mXS4XmQ...7c8J1SL5UHXzIT


PART A:

I made the mistake of assuming this was the primary cause of the knocking issue. In reality, it may have just been a byproduct of the failure outlined in part B, but still may be relevant info to some.

One source (or symptom, as I later discovered) of this knocking sound is only pertinent to these PHEV vehicles that have a front-side, belt driven starter with a one-way-clutch.

The way the PHEV specific N20 works, there is a toothed "traditional" starter motor mounted below the oil filter housing. Oriented "backwards", with a toothed gear protruding out front of the engine. This starter drives the only belt on the front of the engine. It engages the one-way-gear on the crank hub to start the engine. The engine can also be started by the hybrid electric motor in the transmission. These two items allow for a somewhat redundant engine starter setup.

This starter is commonly mistaken as some sort of PHEV A/C pump, or PHEV alternator. It's nothing more.

This clutch/harmonic-balancer-combo had well worn bearings, allowing for the toothed one-way gear to rattle in sync with engine RPM. To check this, I removed the belt and was able replicate the rattle of the one-way-clutch with my hand.

You can use an automotive stethoscope while the engine is running. This may be a future maintenance item for many 40e owners.

Part in question is not cheap. If you'd like to save some time and rule it out, you can temporary remove the belt and replace the crank pulley with the standard one from any N20 or N26. The car will fall back on the hybrid motor to start the engine.

Part: 11238651961

Number 2 in the realoem diagram for "Belt drive - starter"

https://www.realoem.com/bmw/enUS/sho...diagId=11_5841

PART B:

After replacing the part specified in part A, the car ran quiet and well for a while. Unfortunately, the knocking eventually returned exactly as before. I believe this was a result of the fresh bearings and grease in the new crank pulley wearing in, and loosening up a bit.

This knocking from the crank pulley/starter clutch unit ended up working as an early warning system for a much larger and potentially catastrophic issue concerning the dual mass torsional vibration damper between the engine and transmission. Seems the knocking was translating from one end of the crankshaft, to the other. This torsional vibration damper is mounted on the rear of the engine where the torque converter would normally be.

It is essentially a dual-mass flywheel with a splined output. Similar to those seen on BMWs with the 7 speed DCT, but with no teeth for a traditional starter motor. See part A for the starter situation on the 40e.

It was on the cusp of absolute destruction. The inner section was basically just floating around. All of the rivets and fasteners on the face were completely sheared off. I could move the output splines with my hands

I was really fortunate to catch it before it went completely. No damage to the transmission, nor engine. I am discovering others weren't so lucky, losing entire engines or transmissions as a result of just how bad this dual mass flywheel can explode.

I was warned of this possibility by a few vague posts online, and some videos from outside of the US. Hard to find much else for the 40e. No bulletins, nor recalls. Quite a few complaining of some mystery knocking noise, though.

In reality, this is just another typical case of a dual mass flywheel having a problem, which is nothing new for BMW.

There is no reasonable way to inspect this flywheel without removing the transmission. There are no access holes in the bell housing, and there is a bell housing extension installed that prevents removal of the oil pan, or any other means of access.

BMW part number: 21208650161
Sachs/ZF part number: 2295 002 040
Sachs/ZF is the OE. None of the options are cheap. No aftermarket, or second hand market as of now.

Here is my video of the issue: https://youtube.com/shorts/KGRMLU5tp...flmCz5l1aAsWlh

It absolutely sucks how expensive this issue will be for anyone with a higher mileage 40e to to take care of as a preventative measure. Considering the high voltage hybrid drive, extra electronics, and extra cooling: removing the transmission from the 40e requires more time, additional precautions, and a high voltage certified technician at BMW. There will be no need to have your flywheel inspected, because the only reasonable option will be to replace it when you've already paid someone thousands just to get to it.

Thanks for reading. I hope this provides insight to some 40e owners out there.

[Yakis]

Any update ? https://streamable.com/jb4tyc

For me the same sound, like in the first video.

And it's make me angry now.

[ProjektAutoScott]

Originally Posted by Yakis

Any update ? https://streamable.com/jb4tyc

For me the same sound, like in the first video.

And it's make me angry now.

Yes, unfortunately. You can see my edited post above.

It was a failing torsional vibration damper, or dual mass flywheel.