put 300 heads on my 340 now the intake wont seal right, when it get hot and I spay brake cleaner on it the engine runs real bad. I thought the heads were the same. I know the blocks are not.
Do you have the correct gaskets? Intake gaskets for the 1964 aluminum heads are different than the 65-up iron heads.
The heads are identical. Maybe the heads you put on have been severely machined. Look at the accessory hole boss at the bottom of the head towards the intake side, it should be rounded at the bottom or slightly flat. If it's totally flat the head has been resurfaced too many times. Also, as Walt said, if you put 64 gaskets on they will not seal properly. Why did you change the heads?
the only reason I changed them is they had hardened seats. there was nothing wrong with mine. I am in the process of changing back. there are two sets of intake gaskets in the kit ,does it matter witch one I use.
One set of intake gaskets is for the iron heads, the other set is for the aluminum heads. They are different. Use the wrong ones and you get leaks. Maybe you put the wrong ones on your engine.
Use the big ones. I have a friend who had hardened seat put in an Olds motor and had major valve lash problems.
