Coupla reasons.

Rust between bolt and block offers thermal resistance so heat transfer
from bolt to block is limited. That's good: the bolt is disposable,
don't care what we do to the bolt with heat.

Rust is a surprisingly good insulator. If you doubt that, watch the
guys at Midas cut a longitudinal slit in an exhaust pipe or muffler
with a torch, without harming the inside pipe at all.

You can get the bolt very hot without heating the block much at all,
if you use a concentrated heat source as O/A or an arc.

Expansion of the bolt in the hole will both crush and shear some of
the weaker rust. When it cools there'll be more clearance -- Kroil
may go where it wouldn't go before.




On 9 Mar 2004 05:35:02 -0800, (Don) wrote:

I am curious, is it best to heat the bolt head itself or around the
bolt? Will Heating the bolt heat make it more prone to snapping off?

It seems heating a bolt would make it expand, making it tighter?

By the way on all the other bolts I removed there was no rust.