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human
Why is it that brake rotors don't technically warp but cylinder heads and blocks can and do?

I'm a mechanic by trade and I went to school for it for many years at night while I was in the early stages of my career but I just recently found out in another sub that brake rotors don't actually warp due to heat. I did some research and it appears from the few minutes I looked into it that brake rotors develop high and low spots due to uneven brake pad wear which causes the pulsation you feel as the driver if there is a problem. According to the research I did because the brake rotors are manufactured at extremely high temperatures they are impervious to the heat generated by the act of braking meaning that if there is an issue causing a pulsation it must be due to something other than a warped rotor. I like many other mechanics have been describing this issue incorrectly for my entire career according to what I read. That aside I got to thinking, why is it that brake rotors can't warp from the act of braking but cylinder heads can warp from overheating? The typical temperature of the coolant in the engine during normal operation is about 200 to 240 degrees Fahrenheit the actual temperature of the metal in the engine I'm not sure of but I would guess it's in the 300-500 Fahrenheit range. I would also guess that during a severe overheat the temperature might double or triple but not reach the temperature of the manufacturing process. Can someone explain how a big chunk of metal can actually warp due to an overheat condition but not a small brake rotor.
gpt
A cylinder head (or block) is a big chunk of aluminium alloy with a great deal of very uneven stress on it. Parts of it are extremely hot, but most of it is nowhere near hot enough to effect its structural integrity. The uneven heating (and thus thermal expansion) and stress have more to do with warping one than softening due to temperatures outside of the region very close to the cylinder. They are also engineered close to tolerance for weight reasons. There is also even more stress if the engine overheats due to water trying to turn into steam.

A brake rotor is a single piece of high tensile steel (much harder and more heat resistant than alloy), engineered to have a great deal of surplus strength because safety trumps weight. It is heated fairly evenly and the stress is relatively even in one direction. By the time they are hot enough all the way through to warp due to getting soft with this stress, you are doing things like boiling your brake fluid, and you have some serious brake fade going on. It wouldn't surprise me if rotors **do** warp under race conditions or if people persist when going down a mountain range a long time after they start to fade, but this is not typical use, and it would also require some asymmetric pressure. Also if they buckled then the car would stop immediately, you wouldn't see them warp a half mm.

Finally, i have seen a slightly-warped brake rotor, but it was on the front wheel of a motorbike that did somersaults through a paddock. It was the massive blow (which completely wrecked the forks and bent the frame) which misaligned the rotor a tiny, barely perceptable amount.