Cold start rattle 2-3 seconds then gone.

[Slideways]

my bushings are acl with original m10 screws...has anyone mounted the standard acl?

Redish uses that combo. Here is an example with plastigauge measurement:

[bavarian3]

!! BIG UPDATE !!

I THINK WE HAVE OUR CULPRIT! The noise definitely appears to be rod bearing / bolt related. So, good news on finding the cause, bad news that it isn't a cheap fix for others that might be experiencing it.


The BE bearings were trashed. Note that these had ~300 miles on them, they were installed in January of this year (2024). The stock rod bearings from 2005 looked way better than these. Very, very lucky that the crank was undamaged.

They were all installed and torqued properly, however this was part of the "bad batch" - and it shows.


New WPS bearings going in, and sending the BE's back for investigation.

What the ... f

[bavarian3]

please do follow up with your blackstone analysis. curious to see if this could've been caught.

[Andratch]

please do follow up with your blackstone analysis. curious to see if this could've been caught.

IMO, this *was* catching it. This scenario is a little unique from the typical rod bearing failure. This was likely some combination of improper torque/stretch specs at install, and/or a bad batch of bearings from the manufacturer.

This set of bearings only lasted a few hundred miles, but in that time they started knocking/rattling on cold start when oil pressure was zero, and then after they wore more I started hearing a soft knock above 2k rpm. I’d be shocked if the oil analysis doesn’t come come back with crazy amounts of copper.

I don’t have the car back yet, but I did drive by the shop today and see that it’s parked off the lift so they must just be doing quality checks and test drive now.

[bavarian3]

IMO, this *was* catching it. This scenario is a little unique from the typical rod bearing failure. This was likely some combination of improper torque/stretch specs at install, and/or a bad batch of bearings from the manufacturer.

This set of bearings only lasted a few hundred miles, but in that time they started knocking/rattling on cold start when oil pressure was zero, and then after they wore more I started hearing a soft knock above 2k rpm. I’d be shocked if the oil analysis doesn’t come come back with crazy amounts of copper.

I don’t have the car back yet, but I did drive by the shop today and see that it’s parked off the lift so they must just be doing quality checks and test drive now.

Yes. and kudos to you for catching it. In the first video(although it's a video) I really can't hear any abnormal "rattle". In the latest video however, you can hear it.

[BL92]

Good catch, so was it the ARP bolts or incorrect install on the m10s? i hope this is no cost to you!
What about the oil pump? did they check that ?

[Andratch]

Good catch, so was it the ARP bolts or incorrect install on the m10s? i hope this is no cost to you!
What about the oil pump? did they check that ?

No cost to me. This was with OEM bolts, not sure yet if they were torqued correctly or not.

[Andratch]

!! RESOLVED !!



The shop confirmed that my issue has been resolved.

No noise heard on several starts between friday and today, giving about 24 hours between each start. New WPS bearings and ARP bolts have been installed, torqued properly to spec, and we're good to go.

There's certainly a possibility that other folks' noise could be caused by other things, but as a summary, here is the sound that I experienced:

https://www.youtube.com/watch?v=LnS6MEOxo7U

Here are the symptoms I observed:

1) Rattle/knock on first cold startup (after oil pressure bled off), with a 'tempo' consistant with bottom end issues (1:1, not not 2:1 that you'd hear from top end / vanos)
2) Over a few weeks, started to hear a soft knock above 2k rpm (again 1:1)
3) I pulled an oil sample that I assume will show massive amounts of material wear, but I did not obvserve a ton of metal flake in the filter.

I tried the resolutions below with no fix:

1) New Chain Tensioner
2) New Oil Filter Housing
3) New oil/filter, 10W60 BMW Brand
4) New VANOS accumulator
5) Disable cold start cycle in ECU

The root cause turned out to be either a bad batch of bearings, and/or improper torque of the rod bolts. Either way, this noise was indicative of a failure around the bearings that could have been catastrophic. If you're experiencing this sound, don't leave it to resolve itself!

[Slideways]

Not sure what to make of this, but in the picture you posted with the tech torquing the rod bolts, those appear to be ARP rod bolts.

[Andratch]

Not sure what to make of this, but in the picture you posted with the tech torqueing the rod bolts, those appear to be ARP rod bolts.

I think that picture is reassembly, I told them I was okay with ARP bolts if they torque them to stretch specs. I'm going by today to pick up the old bolts and will post pictures.

[Andratch]

I think that picture is reassembly, I told them I was okay with ARP bolts if they torque them to stretch specs. I'm going by today to pick up the old bolts and will post pictures.

Below is a picture of the bolts that were removed. OEM.

[Giulianomitaly]

Good morning everyone...it seems that I too have solved the problem of the noise at first start-up....my bearing had been changed 8000km ago with acl ones...2 were out of tolerance, when I installed them they were ok.. .now I have mounted everything OEM BMW hopefully

[bavarian3]

Good morning everyone...it seems that I too have solved the problem of the noise at first start-up....my bearing had been changed 8000km ago with acl ones...2 were out of tolerance, when I installed them they were ok.. .now I have mounted everything OEM BMW hopefully

Which ACL bearings did you use? Did you plastigauge on install?

[Giulianomitaly]

Yes i used plastigauge and had a tolerance of 0.051 on all… my ex bearing is acl 6b1569h-std

[bavarian3]

Yes i used plastigauge and had a tolerance of 0.051 on all… my ex bearing is acl 6b1569h-std

What do the bearings look like now?