Download Remove outer (upper) timing chain. See TIMING CHAINS . Remove idler sprocket and shaft. Prevent camshafts from turning, and remove camshaft sprocket bolts. Remove camshaft sprocket. Mark and remove camshaft bearing caps in reverse order of installation. See Fig. 30 . Remove camshafts. 2. Loosen cylinder head bolts in 2 or 3 steps, in reverse order of tightening sequence. See Fig. 31 . Remove camshaft sprocket cover. Remove outer (upper) chain tensioner and guide. Remove outer timing chain. Remove idler sprocket bolt. Remove cylinder head. Inspection (240SX, Altima & Frontier) 1. Inspect timing chain roller links. Replace timing chain if roller links are cracked or worn. Inspect cylinder head and cylinder block mating surfaces for warpage. If warpage exceeds specification, machine cylinder head. See CYLINDER HEAD (EXCEPT 1997 PICKUP) table under ENGINE SPECIFICATIONS. 2. If machining reduces cylinder head height to less than specification, replace cylinder head. After machining, rotate camshaft by hand.