Cast iron, heated, then cooled rapidly

[daverclasper]

Hi. I need to remove a manifold bolt, that has rusted into the head. The thread of bolt is accessible, where it goes into head. I was thinking of using mapp gas torch to heat, then quashing with water/pen fluid, to shock it free.

Any problems doing this with it being cast iron, please.

Thanks, Dave    

[JohnD]

The head itself provides enormous heat sink potential, so rapid heating is desirable.    Weldiing a nut to the end of the bolt will do this and make getting the bolt out afterwards easier.  Always use a to-and-fro  motion like using a tap.   If the bolt squeals stop!   Its about to break!  Turn itback add penetrating oil, wait!

An alternative penetrant is candle wax!    Quench the not bolt with a candle end, getting the wax to the base.   Let it cool heat again, and try as above.

J.