Which cylinder heads should not be cleaned by glass beading?

Cylinder heads made of aluminum should generally not be cleaned by glass beading, as the process can remove too much material and affect the surface finish, potentially leading to issues with sealing and performance. Additionally, heads with intricate passages or those that have been machined for specific tolerances should be avoided, as glass beads can clog or damage these areas. Instead, methods like chemical cleaning or media blasting with softer materials are recommended for such components.