Volunteers wanted for a simple experiment on your old tin/alu rod bearing(s)

[IamFODI]

Originally Posted by CSBM5

Is it possible to wear down the Ti/Al bearings in a running engine enough to get to this copper layer?

Theoretically.

Originally Posted by CSBM5

Conversely, is there an unwarranted freaking out over what appears to be "worn" bearings (since they don't look like brand new ones) when in fact there is plenty more babbitt to wear away before getting to the final copper layer underneath?

Sure looks like it.

Important to note that the "discoloration = excess wear" idea has always been suspect and long overdue for a reckoning. The discoloration has been observed on bearings with fewer than 10k miles – a fraction of how long these engines routinely run in service. Zero chance of that happening if the discoloration meant copper.

Glyco, the manufacturer of these bearings, has said that some of their bearing materials produce a thin layer of surface oxidation in use. Their published guidelines also explicitly describe how a tiny amount of localized surface wear combined with tight clearances (sound familiar?) produces good conformability even with robust bearing materials. Far more likely that this is what we're seeing.

[Assimilator1]

Originally Posted by CSBM5

Is it possible to wear down the Ti/Al bearings in a running engine enough to get to this copper layer?
Conversely, is there an unwarranted freaking out over what appears to be "worn" bearings (since they don't look like brand new ones) when in fact there is plenty more babbitt to wear away before getting to the final copper layer underneath?

1. Yep, just we've not seen it here yet AFAIK.

2.Barring what IamFODI said about some of Glyco bearings allowing to have a tiny amount of wear, in general the babbitt layer is not intended to wear away, it is meant to stay there the life of the engine (likely at least 200k miles) with no copper ever meant to be exposed. The babbitt is there to protect the crank from scoring by any debris and when starting or stopping the engine when oil lube is briefly insufficient.

[Assimilator1]

[edit]wth is going on with this forum? I've already replied, lol.] Sorry, somehow I missed your message (I don't recall getting a notification).

Re 1st question, I don't see why not, it's happening with the lead/copper bearings.
2. With the tin/alu/copper bearings, I'd say a very cautious and weak 'maybe'.
The problem is the babbitt isn't really meant to wear out, unless you're talking starship mileages! Lol, think 200k+
Also, we don't know how much babbitt is left even when no copper is showing. If it's a tenth of it's original thickness, could it still be safely embed any debris? Probably not I would think.
So atm it would appear the risk is less with the later bearings, but not down to normal (near 0) levels.

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Added another rubbed bearing link to the op, the poster, E90M3Ross from m3cutters's bearing hadn't gone through to copper .