On the Concorde engines, it was said that when they were started a certain RPM had not be exceeded for a certain period of time as the main rotor shaft through the middle of the engine bent slightly during cooling after last running. To exceed this certain RPM too soon would wreck them until the shaft straightened (probably only a thousandth of an inch or so).
Can anyone verify this, Concorde experts? If so, possibly the same could have been true for the R-R Tyne engines in the Vanguard.

Quite correct. Can’t recall the exact details of use of engine debow, but it was part of the start cycle where the engine was held at a certain %age until the yellow debow light in the switch(es) went out, when the engine would then accelerate up to ground idle.

There are 4 debow switches on the FEO’s leg panel, and I THINK debow starts were carried out on the ‘turn-around’ and after the aircraft had been shut down for a shorter than specified time.