BMW M5 Forum and M6 Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
48 Posts
Discussion Starter #1
Are you an expert on the S85? Do you have what it takes to diagnose what BMW themselves have taken three weeks to misdiagnose twice?! Do you just feel like giving your 0.02? Is your name Troy? Well this thread's for you. :1zhelp:

I've felt like a regular member on this forum for nearly three years. Since 2011, I've searched and satisfied countless questions of my own - this board my one and only resource. Enough searching, that I felt like an expert on the E60 and all it's foibles.

So when on October 4th, I felt an almost indescribably subtle judder and heard an almost inaudible noise shifting from high third into fourth, I gave pause and continued my drive a little longer than I would have otherwise, just to make sure it was just my imagination.

It wasnt.

Two miles later, coasting to a red light, I received an Engine Malfunction warning, and a few seconds later, the engine dropped from a hum into jerking and juddering. I was a quarter mile from home and nursed her back to my garage, doing 25mph in third to keep as little pressure and revs on the engine as reasonable. All the while one thought going through my mind. Rod bearings! Rod bearings!!

Next day, had her towed 150 miles from Wisconsin back to Laurel BMW where I regularly get service. Shes's been there since Sunday the 5th.
Fast forward nearly three weeks, and after multiple leakdown and compression tests, multiple cylinder head disassemblies, timing tests, boroscope inspections, swaps of coil packs, spark plugs, injectors, and upper-engine ancillaries, rod bearings have still not been a consideration by the dealer as the culprit. Maybe it's not, but as for the multiple misdiagnoses, both times - by the regular service techs, and by the lead tech - it was diagnosed as a broken valve spring.

It wasnt!

They have been going off of irregular and often failing compression in just one cylinder - cylinder 4. So the latest assumption is that it could be a piston ring.

Do you think it could be a rod bearing? The rough, bouncing idle and rev helped convince me that it could be, with cylinder 4 potentially improperly aligned with the crankshaft, the whole firing order would be compromised, creating a juddering power delivery. So feel free to ask any questions of me you want. I'd love to know what you think has caused this rather great misfortune. In the mean time I'll have my foot to the floor in the fastest car I've ever driven, my loaner 528i. hiha
 

·
Registered
Joined
·
13,461 Posts
Wow not even checking the oil for metal shavings or sending it out for a quick analysis, I mean its been over 2 weeks and that would have been an easy thing to check to see if there was a rod bearing issue.

Don't they have a master tech for these cars as I know the dealership where I live told me they have a specialized tech to deal with M models.
 
  • Like
Reactions: noM5where

·
Registered
Joined
·
48 Posts
Discussion Starter #6
At this point are they not going to drop the bottom and Rod bearings to get to the cylinder?
Nope, they still won't do it! Next on their to-do list is removing the whole cylinder head instead of just the valve covers.

What did the oil filter look like?

Metal in oil when they drained it out of the pan?
I haven't heard anything about them draining the oil... after all they don't want to replace it every time they have to move it in and out of the shop. LOL

Don't they have a master tech for these cars as I know the dealership where I live told me they have a specialized tech to deal with M models.
Yes, and I met him last Thursday. He says he's been with the dealer for 18 years and has not once seen a car come through needing a bearing replacement. I find that especially funny because my father's '11 550i already had its engine replaced at 21,000 miles due to "worn/sheared conrod bearings"

you might have a broken valve on that cylinder that fails the compression test.
I'll be sure to mention that to them next chance I get. And pray that it isn't it!!
 
T

·
Guest
Joined
·
0 Posts
ImageUploadedByAutoGuide1414073220.009411.jpg ImageUploadedByAutoGuide1414073261.623337.jpg ImageUploadedByAutoGuide1414073279.370816.jpg

It is highly exceedingly unlikely that this is the problem. However, one of the motors we just took out of a car as a core motor had broken edges on the valve.

2008 m5, 71k miles. Happened on the Dyno at around 6600rpm on a pull. Owner drove 750-miles with a slight tapping and misfire until sending us his car. He bought the M5 with 69800-miles on it.
 
T

·
Guest
Joined
·
0 Posts
Change the oil and change the oil filter. If there is metal, then you know the motor failed. That should be the first thing to do, even before a compression test
 

·
Registered
Joined
·
779 Posts
Yea listen to troy, this would have saved my buddy 2 months of waiting and saved the shop 8k as it did not fix the issue.

He needed a new engine the entire time not a vanos pump
 

·
Registered
Joined
·
116 Posts
A spun bearing won't cause low compression in the cylinder would it?
Atleast not until the rod goes through the block and that should be pretty obvious....
 

·
Registered
Joined
·
48 Posts
Discussion Starter #11
Thanks Troy, I'll be sure to suggest that as a next course if lifting the cylinder heads doesn't produce any new information.
 

·
Registered
Joined
·
48 Posts
Discussion Starter #12
A spun bearing won't cause low compression in the cylinder would it?
TBH I'm not entirely sure..

My theory is that if there's no longer an upper bearing between the crank and the rod, then it's not being lifted as high by the crank as is usually expected, thus less dense air in the cylinder at the top of the stroke.
 

·
Registered
Joined
·
1,131 Posts
TBH I'm not entirely sure..

My theory is that if there's no longer an upper bearing between the crank and the rod, then it's not being lifted as high by the crank as is usually expected, thus less dense air in the cylinder at the top of the stroke.
Is the engine knocking? This if a bearing spun the engine should be knocking.
 

·
Registered
Joined
·
779 Posts
A spun bearing won't cause low compression in the cylinder would it?
Atleast not until the rod goes through the block and that should be pretty obvious....
I guess if you had a lot of metal in the oil it could score the cylinder walls and make low compression?

Highly unlikely but possible maybe?
 

·
Registered
Joined
·
48 Posts
Discussion Starter #15
I cannot remember hearing a highly discernible knock, but what do I remember anyways, it was near as makes no difference, three weeks ago now.
 

·
Registered
Joined
·
48 Posts
Discussion Starter #16
I guess if you had a lot of metal in the oil it could score the cylinder walls and make low compression?

Highly unlikely but possible maybe?
Interestingly enough, I was recently informed that they saw no scoring on the cylinder wall after using the boroscope to look inside.
 

·
Registered
Joined
·
6,632 Posts
I would be surprised if was a bad bearing. If the bearing is gone and the rod and crank journal are worn enough to fail a compression test it will be knocking terribly. My money would be either bad piston rings, if you get an oil analysis the flash point should be low as there is likely petrol in the oil, or as Troy said damage to the valves themselves.

Good Luck. And enjoy the N20 powerhouse.
 
1 - 17 of 17 Posts
Top