I have never measured it. It may vary depending on the particular babbit metal used. But I have always used 350 °F as the expected melting temperature. However, I would never deliberately run a babbit bearing at an operating temperature above 250 °F.
The common tin-base and lead-base babbits are specified in ASTM B23. For high performance rotating equipment,tin-base is the choice, and the lead should be specified as low as possible.
For ASTM B23, Babbit types /melting temperature deg F
1 433
3 464
4 363
5 358
7 464
10 468
11 471
12 473
16 471
19 462