Spun Rod Bearing - 2004 M3

[Desert_M3]

A couple weeks ago, this owner brought his M3 over to my garage to have me listen to the noise it was making. Parked and idling in my driveway, nothing was heard. In fact, there was zero knocking/rattling until about 4000rpm! The noise was noticeably louder when listening underneath the car. I figured it could be a spun bearing, but was a bit skeptical seeing as it was a very faint noise at only 4krpm+.

He again dropped his car off, for me to perform a rod bearing service. This particular car is a 2004 with almost 175k miles. Check out what I found:

https://www.youtube.com/watch?v=2FypQ2PwVRU

and

https://www.youtube.com/watch?v=LHfKg9fCMQY

I understand 175k miles is a lot, but know your 2003.5-2006 M3 is not immune to rod bearing issues!

That being said, if you're in SoCal and want your rod bearings changed, vanos bulletproofed, valve adjusment, or almost any other service/install, shoot me a PM on here or on instagram @sandiegoS54 and we'll get you taken care of!

[eacmen]

How did the crank journals look?

[Desert_M3]

How did the crank journals look?

I'll grab photos tomorrow and post them here. Honestly it looks fine, but this is the first time I've found a spun bearing. Going to get a second opinion tomorrow as well.

[Arith2]

Rub your nail across, and also measure with a set of calipers and compare to other journals.

Here's that picture. Can see the grass on the other side.

[Desert_M3]

Rub your nail across, and also measure with a set of calipers and compare to other journals.

Here's that picture. Can see the grass on the other side.

Yikes, thats insane. I dont feel any scoring on the crank, seems pretty smooth. I'm still skeptical of just tossing new bearings in there though..

[George Hill]

I saw the video where the bearings had spun on the crank. Honestly even if the crank looks good I would be concerned the big end of the rod is not ovaled. When the rod clearance opens up (causing the knocking) the rod is getting hammered on the crank which makes the big end elongate or oval. This causes it to not have the correct clearance with the new bearings. I tried to save one in similar condition (it was my own car and an experiment as much as anything) and it lasted 1200 miles before it spun again. Good luck, YMMV

[Desert_M3]

I saw the video where the bearings had spun on the crank. Honestly even if the crank looks good I would be concerned the big end of the rod is not ovaled. When the rod clearance opens up (causing the knocking) the rod is getting hammered on the crank which makes the big end elongate or oval. This causes it to not have the correct clearance with the new bearings. I tried to save one in similar condition (it was my own car and an experiment as much as anything) and it lasted 1200 miles before it spun again. Good luck, YMMV

Good point. Talking with the owner, we decided not to risk it. Currently looking for a good used crank in SoCal. If we cant find one, he'll have Lang repair his current crank. I think this guy got extremely lucky given the circumstances, as a spun bearing could have caused a hell of a lot more damage than whats seen on his S54.

[George Hill]

Good point. Talking with the owner, we decided not to risk it. Currently looking for a good used crank in SoCal. If we cant find one, he'll have Lang repair his current crank. I think this guy got extremely lucky given the circumstances, as a spun bearing could have caused a hell of a lot more damage than whats seen on his S54.

Sorry I should have been more specific, the damage isn't necessarily to the crank, but to the connecting rod itself. I would be more concerned the rod is damaged and you won't be able to determine this by eye, you would need to take precise measurements.

[Arith2]

Need them 'ole T-guages. It'll be very difficult to get accurate measurements with the piston in. Try the easiest option and try to measure with them in. It's good to measure down to the ten thousandth but not particularly required. Most manufacturer specs go to the ten thousandth so that's why I mention it. The allowable tolerance may be around .0005" but I have no idea what it actually is for our engines. I'll try to find a manual or publication on it. Some who worked for BMW may have the manual for it.

[Desert_M3]

Sorry I should have been more specific, the damage isn't necessarily to the crank, but to the connecting rod itself. I would be more concerned the rod is damaged and you won't be able to determine this by eye, you would need to take precise measurements.

Right, but I'm just going to guess the crank is damaged as well. In any case, I have spare connecting rods that I'm willing to give to him should he need any.

[Syfon]

I just pulled my S54 crank. Spun rod-bearing #3; there was no copper left on the bearing. Scored crank journal #3. Main bearing #4 is also damaged, as is the corresponding journal.

I'm doing a full tear-down in my garage.

Few pics

[Arith2]

Yeah that crank looks shot.

[Dash1]

I just pulled my S54 crank. Spun rod-bearing #3; there was no copper left on the bearing. Scored crank journal #3. Main bearing #4 is also damaged, as is the corresponding journal.

I'm doing a full tear-down in my garage.

Few pics

How many miles on your bearings?

[Syfon]

How many miles on your bearings?

93,000KM (approx. 57k Miles)

Original bearings.

[Desert_M3]

93,000KM (approx. 57k Miles)

Original bearings.

Yikes, thats low miles to be spinning a bearing. Although there are more factors than just mileage.