UOA vs. Actual Bearing wear

[Nate1979]

Originally Posted By: Clevy
Originally Posted By: OVERKILL
Not surprising in the least. Those of us familiar with the limits of UOA's (thanks to Doug Hillary's excellent and extensive posting on the subject) know that their primary purpose is to monitor oil life and contamination, not as a wear-monitoring tool.

I hope every single member here sees this post. I was told in a thread the other day I was wrong when I said this very same thing.
Some people are just thick.
K back you your regularity scheduled programming.


Wow! what a great quote.

 

[S12]

Originally Posted By: SteveSRT8
I remember a street car engine in my youth that had exactly this issue. Torqued carefully to spec it would quickly munch that rod bearing. A piece of plasti-gage measuring stuff showed that the clearance was severely reduced there. I don't recall the explanation, I just used another rod and had no more problems.

It still amazes me that BMW's seem to suffer oiling issues in this day and age, but there is definitely something amiss. Tragic that the enjoyment of a nice responsive vehicle must be tempered with the fear of catastrophic failure...


Its not an oiling problem at all its actually a bearing size issue. On a popular BMW forum some club racers were talking about the S54 bearing failures which are exactly like the S62 failures and one racer posted pictures of a set of S54 bearing next to a set of bearings from an S52 engine which was the predecessor of the S54. The width difference in the bearings was kind of shocking. The old S52 had much wide bearings then the S54 which would explain why the old S52 has always been so resistant to oil starvation at the track. In hard left hand corners S52's with stock oil pans are known to oil starve and hit 7 psi or less oil pressure for a second or two at 6,000 rpm and be just fine. The S54 on the other hand had bearing replacement recalls issued and even today many E46 M3 racers replace their S54 rod bearings every race season due to how fast they wear. Basically the S54 has thinner hearings that have less area to support the high pressure loads of such a high HP, high rpm engine. Its a BMW design flaw and TWS 10w60 is the band aid that BMW has used to nurse it along.

TWS 10w60 isn't that thick of an oil in truth. In 2 or 3K it shears down to a 50 weight and is a 40 weight by the time the oil life monitor is reached. Its the oil film strength that BMW was looking for to help with the bearing loads.