N54 Engine Clank *Not rod bearing related*

jeddo45 · 12-21-2022, 01:07 PM

I got an issue that I, nor my mechanic can't put our fingers on. I'll explain this as detailed as possible hoping that someone else has had a similar issue.

At about 2k RPMs, there is a noticeable slapping/ clank coming from the engine. It also happens on neutral so it's not anything driveline related.

The issue is mainly from 2k to 4k RPMs only when I'm hitting the gas. From idle to about 2k, no clanks or slapping noise. But from 2k to 4k RPMs, its a very loud definitive clanking/ slapping. The noise coincides with the speed of RPMs. When I let go of the gas and the engine comes to an idle, the noise doesn't happen at all no matter where I'm revving the engine.

My timing chain and guides have been replaced but the noise is still there. Since the noise happens only within that RPM range, we don't think it's rod bearing or piston related.

I'm going to try and upload a video and see if you all could hear it. In the meantime, any thoughts? The car runs great still. No noticeable performance drop or limp mode. I'm baffled.

Any suggestions?

https://photos.app.goo.gl/dJeo7zEerPUxM5hR8

Tejas1836 · 12-21-2022, 10:53 PM

Did you own a cat?

GuidoK · 12-21-2022, 11:22 PM

My first guess would be the vibration damper. Or maybe some weird resonance from a belt tensioner or such.
But a clacking sound like that (non intermittent on a stationairy car) shouldn't be too difficult to locate?

If it comes from within the engine (or within a stationairy part), use an engine stethoscope. A cheap and really handy tool.

10" · 12-29-2022, 11:40 PM

I mean at that range from about 2000-2500 is when the N54 twin turbos really start going up to about 4000+ is their peak range—so without knowing much more I’d wonder about the turbos. It’s nothing like the famous wastegate rattle?

XutvJet · 12-30-2022, 11:30 AM

That is absolutely rod knock and the rpm range you're noting is the common rpm range that it tends to be most audible. I'd find another mechanic if they couldn't tell that was rod knock within one engine rev.

chris719 · 12-30-2022, 01:42 PM

I have to agree with XutvJet that it does sound like rod knock.

tracer bullet · 12-30-2022, 02:33 PM

I've heard sticky (open) injectors sound like rod knock.

meadowsdb · 12-30-2022, 02:58 PM

Rod Knock. Keep your foot off it before you have a hole in the block.

TheMidnightNarwhal · 12-30-2022, 03:14 PM

Unfortunately does sound like rod knock. That said, I would try to run the car with the serpentine belt removed just to rule out any accessories. I've read in the past someone who thought he had rod knock on his N54 but it ended up being the AC compressor. Good thing to try and rule out (unless your mechanic already did it).

12-21-2022, 01:07 PM	#1
jeddo45 Apprentice 376 Rep 801 Posts Drives: 2007 BMW 335i Join Date: Jul 2016 Location: LBC iTrader: (0)	I got an issue that I, nor my mechanic can't put our fingers on. I'll explain this as detailed as possible hoping that someone else has had a similar issue. At about 2k RPMs, there is a noticeable slapping/ clank coming from the engine. It also happens on neutral so it's not anything driveline related. The issue is mainly from 2k to 4k RPMs only when I'm hitting the gas. From idle to about 2k, no clanks or slapping noise. But from 2k to 4k RPMs, its a very loud definitive clanking/ slapping. The noise coincides with the speed of RPMs. When I let go of the gas and the engine comes to an idle, the noise doesn't happen at all no matter where I'm revving the engine. My timing chain and guides have been replaced but the noise is still there. Since the noise happens only within that RPM range, we don't think it's rod bearing or piston related. I'm going to try and upload a video and see if you all could hear it. In the meantime, any thoughts? The car runs great still. No noticeable performance drop or limp mode. I'm baffled. Any suggestions? https://photos.app.goo.gl/dJeo7zEerPUxM5hR8
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12-21-2022, 10:53 PM	#2
Tejas1836 Captain 1058 Rep 904 Posts Drives: 2023 X5MC Workmaster 75 Join Date: Oct 2022 Location: Tejas iTrader: (0)	Did you own a cat?
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12-21-2022, 11:22 PM	#3
GuidoK #buildnotbought 13344 Rep 5,425 Posts Drives: Z4 3.0i ESS TS2+ Join Date: Jul 2012 Location: Tinkering in the garage iTrader: (0)	My first guess would be the vibration damper. Or maybe some weird resonance from a belt tensioner or such. But a clacking sound like that (non intermittent on a stationairy car) shouldn't be too difficult to locate? If it comes from within the engine (or within a stationairy part), use an engine stethoscope. A cheap and really handy tool. __________________ Z4 3.0i \| ESS TS2+ supercharger \| Quaife ATB LSD \| Brembo/BMW performance BBK front/rear \| Schrick FI cams \| Schmiedmann headers+cats \| Powerflex/strongflex PU bushings \| Vibra-technics engine mounts \| H&R anti rollbars \| KW V3 coilovers/KW camber plates \| Sachs race engineering clutch \| tons of custom sh#t
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12-29-2022, 11:40 PM	#4
10" Colonel 5108 Rep 2,297 Posts Drives: orange BMW 1M. Join Date: Jun 2018 Location: world iTrader: (0)	I mean at that range from about 2000-2500 is when the N54 twin turbos really start going up to about 4000+ is their peak range—so without knowing much more I’d wonder about the turbos. It’s nothing like the famous wastegate rattle? __________________ don't read this. too late...
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12-30-2022, 11:30 AM	#5
XutvJet Major General 5929 Rep 5,520 Posts Drives: 2011 Cayman Base, 2016 M235 Join Date: Mar 2016 Location: Kansas City iTrader: (-1)	That is absolutely rod knock and the rpm range you're noting is the common rpm range that it tends to be most audible. I'd find another mechanic if they couldn't tell that was rod knock within one engine rev.
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12-30-2022, 01:42 PM	#6
chris719 Major General 7585 Rep 7,520 Posts Drives: '08 M Roadster Join Date: Oct 2007 Location: NJ iTrader: (0)	I have to agree with XutvJet that it does sound like rod knock.
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12-30-2022, 02:33 PM	#7
tracer bullet Brigadier General 3679 Rep 4,220 Posts Drives: '25 Z4, '15 X3 35i (135i sold) Join Date: May 2011 Location: Saint Paul, MN iTrader: (1)	I've heard sticky (open) injectors sound like rod knock.
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12-30-2022, 02:58 PM	#8
meadowsdb Private 73 Rep 99 Posts Drives: '20 M8 Comp Grand Coupe Join Date: Mar 2019 Location: Los Angeles, CA iTrader: (0)	Rod Knock. Keep your foot off it before you have a hole in the block. __________________ Rides-- '17 M3 CP-CAI, Dinan Stg 1 '17 Camaro ZL1 (700HP) '15 Audi S4 (500 HP) '15 Charger Hellcat (1050 HP)
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12-30-2022, 03:14 PM	#9
TheMidnightNarwhal Major General 2800 Rep 6,382 Posts Drives: 11' 335is DCT Join Date: Jun 2015 Location: Gatineau, Quebec iTrader: (0)	Unfortunately does sound like rod knock. That said, I would try to run the car with the serpentine belt removed just to rule out any accessories. I've read in the past someone who thought he had rod knock on his N54 but it ended up being the AC compressor. Good thing to try and rule out (unless your mechanic already did it).
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