The Russkies had the same problem. Unable to make precision bearings that would endure extreme duty. In the book, “MIG PILOT”, subtitled, “The Final Escape of Lt. Belenko,” after he had defected to the west via Japan, as he was being debriefed by our people, we were amazed to learn of the MIG-25’s speed limitations, having tracked one at some ridiculous speed, above Mach-1? I forget.
Anyhow, Belenko stated that the flight we tracked had been staged as a snow job for our people. He said that after that extended burst of speed, the engines were shot and had to be replaced. He said that Russia couldn’t make good bearings.
That was a very revealing book.
The aircraft set over 20 altitude and speed records...and STILL holds 7, inclusive of altitude achieved under it's own power at 123,000ft.
When operated below Mach 2.5 the engines held up to normal timeframes.
However, the aircraft was made from nickel steel alloy, weighed 64,000 pounds and could be seen from several hundred miles away with the most primitive radars.