Help me decide on a UOA plan for my bearing-eating BMW

[d00df00d]

Originally Posted by MolaKule

My suggestion is to send the bearing you are going to be using to http://www.arrowlab.com/ labs and have them do an analysis on the elemental content. Without knowing the metallurgy of your engine components, UOA's will tell you nothing.

Thanks, Mola. AFAICT, it's known with reasonable certainty that the bearings are steel backed with tin/aluminum alloy at the surface. Is that not enough to be reasonably sure that a tin spike might indicate bearing wear?

 

[MolaKule]

Here is what I could find on Al-Sn bearing alloys. Aluminum-tin Alloy 850.0, is 91.7%Al, 6.3%Sn, 1%Cu and 1%Ni Aluminum-tin Alloy 852.0, is 89.7%Al, 6.3%Sn, 2%Cu, l.2%Ni, and 0.8%Mg. If there are no Tin elements in the finished lubricant, such as Tin Naphthenates or SnDTC, or such, one might be able to detect the low levels of Sn from bearing wear with a very careful trending analysis of the oil. One thing for sure, if the bearings start to wear excessively, the Al ppm should certainly spike above a baseline level.

 

[d00df00d]

Originally Posted by MolaKule

Here is what I could find on Al-Sn bearing alloys. Aluminum-tin Alloy 850.0, is 91.7%Al, 6.3%Sn, 1%Cu and 1%Ni Aluminum-tin Alloy 852.0, is 89.7%Al, 6.3%Sn, 2%Cu, l.2%Ni, and 0.8%Mg. If there are no Tin elements in the finished lubricant, such as Tin Naphthenates or SnDTC, or such, one might be able to detect the low levels of Sn from bearing wear with a very careful trending analysis of the oil. One thing for sure, if the bearings start to wear excessively, the Al ppm should certainly spike above a baseline level.

This is excellent! Thanks for digging these up. The oil analysis reports I've seen with the oil I'll be using all show 0-1 PPM Sn, so that's good. Hope they don't change the add pack any time soon! Good to know about Al. Figured that'd be part of it but I didn't imagine it'd be that much. I've also asked for guidance from Glyco, who supposedly makes these bearings. Fingers crossed for a reply.

 

[d00df00d]

Has enough time passed that this qualifies as a necro-bump? The oil analysis kit I've settled on is Polaris's Advanced Engine Plus service. Cost-effective for the kinds of things I'm interested in, and includes a PQ index. Glyco did get back to me with UOA guidance. Predictably, they wouldn't share anything exact about the alloy in these bearings because it's proprietary. However, they said the thing to look for on a UOA would be Al and Sn rising together in a roughly 9:1 ratio. Was asked in another thread about pics of the old bearings. Here they are. Bear in mind that these are the original lead/copper bearings, with just over 80k miles of unknown use on them at the time. Factory oil at OLM OCIs for the first 50k, and then Shell Helix Ultra Racing 10W-60 at OLM OCIs after that.

 

[A_Harman]

Reviewing the thread, you said the bearings were replaced as a preventive measure. I think they generally look good. The upper halves all have the "bullseye" near center where the firing loads are carried. The only one that looks like it is developing trouble is the lower half of 6, where it appears to have some pits left of center.

 

[d00df00d]

Originally Posted by A_Harman

Reviewing the thread, you said the bearings were replaced as a preventive measure. I think they generally look good. The upper halves all have the "bullseye" near center where the firing loads are carried. The only one that looks like it is developing trouble is the lower half of 6, where it appears to have some pits left of center.

5 has copper showing. That means the lead babbit layer has started to wear through. I believe one other pair had some copper showing as well but I can't remember which -- it's more obvious IRL than in the pics.