how to remove heads on a 4.6l northstar engine
If you are asking how to remove heads, the only reason I know of requiring this, is that the engine was overheated. It wasn't overheated just a little bit and for both heads needing to be pulled, the engine might be junk.
Your engine most likely is not worth attempting to change two head gaskets because if the engine got hot enough to blow both gaskets, there is most likely more than head gasket problems with this aluminum engine.
I answer an average of these over heating issues on Cadillacs once a week and yet these questions continue the pop up over the last 10 years.
How about new? If some dealer still has a new crate motor, you are looking at $4k minimum just for the engine without labor and fluids (and you still do not know if you fixed the over heating issue that caused the head gaskets to blow)
Cadillac engineers ripped the consumer off here in my opinion. Either that or their engineers that designed the engine were inferior to those with Renault/AMC and the Alliance and Encore.
If the aluminum engines in their cars were over heated (all the time) and destroyed by the drivers, at least one could still have a good engine block at least, because a piston liner kit was available. The cylinder head may have been warped, cracked or junk, but the block would not be because the pistons and cylinders could be replaced.
I have said it before-trial attorneys really dropped the ball here. They go after anyone they could, but they left GM alone on this issue where 9 out of 10 of these Cadillac engines had over heating issues costing the owner substantial cash. GM made billions and billions on either replacement engine parts, or engines.
One person asked if they should have the head gasket replaced from the dealer. My answer was GM already ripped offed countless people and then you would give them more money to repair their inferior product?
Good luck on those heads!