I know the bottom line is replace the aluminum ones, but a friend brought this up to me. I told him the aluminum ones were intake. His had them on the exhaust, and his dealer's book showed them for the exhaust. His is a newer 18 horizontal and mines a '97 18 horizontal. Wondered if George knew the OEM reasoning behind the steel/aluminum. I thought weight, but maybe it's an expansion issue. I was sure my '97 had them on the intake. But a dealer did replace the shortblock, and the kid that did it wasn't smart enough to set the valves with any clearance.. so he may not have put them where they belonged. Just curious.