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Loosening Head BoltsOne down, one to go. Brice de-torques the second 1MZ-FE head, which involves eight 12-point undercut bolts and one Allen bolt on each head. Bolts allow head removal in tight engine compartments without engine removal, and the undercut narrow between head and thread area enables each bolt to stretch for even clamping forces across the head. Such bolts can't be re-used and the system can't keep the head from lifting at high boost and combustion pressures. We sent them off to ARP for stronger super-duty head studs.