Three- Piece Billet Aluminium Timing Cover CO312Three Piece Billet Aluminium Timing CoverSuit Big Block Chevy CO312 312 The COMP Cams Three Piece Billet Timing Covers for Small and Big Block Chevy engines allow access to camshaft timing adjustments without having to remove the harmonic damper or disturb the oil pan seal. Designed to be lightweight yet rigid, these billet covers offer convenience and performance in one easy to install package