Originally Posted by williaty
There's substantial confusion about wither or not they need to be replaced and it took a long time for me to sort out the truth on it.
The fact that they specify a "torque plus angle" leads a lot of people to conclude that they're "torque to yield" bolts and therefore need replaced every time. On the other hand, the factory service manual doesn't say anything about replacing them each time.
Turns out, they are torque to yield bolts, but they're not *THAT* kind of TTY bolt. Traditional TTY bolts are torqued until they stretch (yield) into their plastic deformation range. In other words, you stretch them and they don't quite rebound to normal. This is why you can't re-use this kind of bolt. It's becoming increasingly common on modern engines to get TTY bolts that are stretched into their elastic deformation range, meaning that you stretch them and they go back to normal when you release them. You can re-use these kind of bolts many times.
That's the first actual explanation I've ever seen about it - most people just say "yes you can reuse them" but can't back it up. Thanks.