I am rebuilding a car engine. With some of the fasteners I am unscrewing, I notice that a lot of torque is required to undo the fastener. It feels like a snap when undoing a fastener, rather than a smooth twist. If I tighten the fastener to a set torque again and loosen it, it requires the same torque as it took to fasten it.
Why would this be? My guess would be something to do with heat cycling.
Note: There is no threadlocker on these bolts.