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Originally Posted by IamFODI
Can we talk about this as well? I have questions, and not the rhetorical kind.
How does the harder material pose a greater threat to the crank? Has this actually been seen to happen? And/or what are the possible mechanisms for that to occur?
I get why this is a sticky idea. Harder = more likely to scratch a given thing rather than be scratched by it. But any bearing material will be way, way softer than the crank. That's literally the point of a bearing material. No one is stupid enough to spec a bearing material that's hard enough to damage a hardened steel crank on its own.
Probably safe to say it's also not a matter of these bearings wearing down to the backing sooner, because we now know the opposite is true.
Reduced embeddability, maybe? More crank-scoring debris floating around? If so, how could the un-embedded debris score the crank without first annihilating the bearing, which doesn't show up much if at all in the pics?
I know harder bearing alloys can have less conformability, which could generate hot spots and inconsistent oil films. Is that it? But if that were happening at scale, wouldn't we see a lot more worn bearings, failed engines, or both? And, as the Glyco document repeatedly cited in this thread says, tight clearances actually improve conformability via very slight, highly localized initial wear – which lines up nicely with what we now know we're seeing in pics of these bearings...
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I haven't forgotten about this, I've been trying to find where in the various literature I downloaded I read about it, not found it yet and I've run out of time now.
It's going to take a while to find I think!