I've found a similar situation when I bore Babbit connecting rods for insert bearings. Original equipment GM rods have much harder bearing material bonded to the big ends than reconditioned ones. The OEM bearing material will actually dull a high speed steel cutter bit, while the recon rods have much softer Babbit in them. I fit Perkins Diesel rod bearings to the spray-oiler rods, at a much lower cost than the dedicated conversion bearings that are getting very scarce and expensive.
Jerry

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