Stretch Bolts In The Head

[BlueBolt 156]

I was just thinking about the stretch bolts that are used for the head. I know that they are a non reusable bolt due to them stretching, but I was wondering when it was that this stretch happened??

 

Is it when they are tightened and torqued up??

 

Or is it once the engine is run and everything comes up to temp??

 

Just a bit of a useless knowledge question really..??

[Razkin 0]

Both, you stretch them when you torque them up and they stretch further as the engine heats up and the material expands.

When the bolts are correctly torqued up the bolts will "reset" itself after the engine cools down again.

 

When you overtighten the bolts, the bolts will stretch but do not "reset" and as a result the head isn't properly clamped anymore.

[BlueBolt 156]

That's kewl, I thought it was a case of it happening when the engine warmed, but wasn't sure what happened once the engine cooled down, figured it would be kinds sitting up above the head and not sealed...