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The last couple of posts in this thread on AACA by Ivan Saxton and Hermlll on babbitt bearing techniques should prove quite interesting to those, like me, with babbitt bearing Packards. See posts #45,46 & 47 in particular.

forums.aaca.org/f120/1920s-rod-bearings-299408-2.html#post974032

I actually disagree with the statement that pouring a bearing into a connecting rod provides superior cooling.

The advantage of the insert bearing comes from "bearing crush" of say .060 or more which creates a press fitting for far superior heat transfer.

In 1935 Packard put an Eight on the oval, opened the throttle, and ran the car 15,000 miles at full speed without failure. Previous tests with poured bearings were providing less than half that before rod bearing failure.

Conversion to insert rods was an approved repair for seventh series and later cars.

Bearing spread and crush also make undesirable the practice of "pulling the pan and checking the bearings" in the absense of any negative symptoms. This is fine for babbit bearings, but for inserts it disturbs the press fit and reduces motor life. Sometimes a little bit of jargon is a dangerous thing.

Yes, it (thin-wall insert bearing technology) was superior, no question. Problem for years (maybe still is) was the availability of the rod inserts themselves.