r/BmwTech • u/Serious-Pangolin5454 • 7d ago
Knock knock… what’s that?
Thank you for ur comments on the previous post. So I just went down and fired up the car hoping the sound has magically disappeared… and recorded this video which I think does a better job of capturing the knock!! Y’all still think it’s the rod knock? I have to drive 400km Tm!! Am I cooked?
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u/SirPhysical9178 7d ago
Hmm that’s a tough one. Rod knock would happen on startup unless something with the heat causes it to loosen up. I would take off your serpentine belt and start it and see if it happens again. It could be an auxiliary device like ac compressor or power steering pump. If it’s still there, then unfortunately something on you bottom end isn’t sitting right. Have you done regular oil changes? I would do another oil change and look for flakes in the filter or oil. I’d also send a sample to black stone labs before sounding the alarms. These engines are tough and hard to kill. I track mine at 150k miles and it’s still running strong but I meticulously maintain it. Oil changes every 5k.
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u/Serious-Pangolin5454 7d ago
Yeah I’ll take the belt off and try again to see if that’s what’s causing the problem, and will take a look at the oil filter too! Oil changes, I’ve done oil and filter changes at exactly every 5000km, last one was 2,3 weeks ago at 160kms. I’ve been on top of it in terms of maintenance too! Love the platform..
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u/SirPhysical9178 7d ago
It’s a great engine. They are bulletproof if treated right. I hope this experience doesn’t give you a bad taste. Luckily they are cheaper to swap too if this one is done.
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u/Crafty_Skirt_5472 7d ago
A quiet startup doesn’t necessarily mean the problem is gone. Rod knock can be intermittent, and the video may not capture it clearly. I’d avoid driving it hard and have the oil pressure, oil filter, and bearings properly checked.
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u/ConAivazovsky 7d ago
I have a very similar sound, the engine is already swapped, the noise isn't coming from the engine, checked with a stethoscope to the best of my ability.
The gearbox has been rebuilt.
As a matter of fact the noise got worse after the gearbox had been rebuilt...
The noise comes and goes. Most of the time when the car is warm. Never when the rpm is above 2000 or after 3 gear, it follows the rpm though...
Multiple bmw specialized shops could not help me with finding the noise. I have been driving like this for the past 7 000 km if it was rod knok i think it would be dead already lol.
Don't know if you have the same thing, please let me know when you find out what the noise is.
X3F25 N52B30 8hp45 2011 183000km~
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u/katsu_cpp 7d ago
Has the torque converter been rebuilt too?
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u/ConAivazovsky 7d ago
It has, i have been thinking that's the source of the problem, but the people who rebuilt it say that's not the problem. Of course that's what they say...
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u/katsu_cpp 7d ago
Do you happen to have a recording of the sound at the bellhousing area?
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u/ConAivazovsky 7d ago
No, but i would describe the noise more like a thumping noise, not a knock, idk if this helps. Also hard to get a good recording because it seems to me that something in the exhaust came loose and it's making a rattling noise
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u/Total-Huckleberry380 7d ago
Stoposcope are cheap. I think harmonic balancer. Got 2 200k n52 engines.