intake bolts

[budDynabuick]

hey all! i recently put my intake on with new gaskets.

i torqued to specs with a accurate wrench. car started and ran great.

next mourning i checked bolts and they had had backed out from 30 to 20 lbs.

these bolts have lost their torque 3 times!!! everytime i

re-torque these bolts and check with carb cleaner it is not sucking air.

but after heating up and cooling down, they lose their torque. do i need new bolts? lock-tight? lock-washers? more torque? btw, the engine is a 1963 215 aluminum. i do not think the intake has ever been removed.

thanks for any and all help.

keith