GM 91177420
Timing Chain

Before starting the camera timing chain and sprocket replacement process begin by disconnecting the battery and removing the timing chain housing. You must extract the spark plugs because they enable easy Crankshaft rotation to set the timing marks. The correct alignment of timing marks must occur before beginning disassembly by ensuring both Camshaft operation requires a 15-degree turn and Crankshaft rotation needs to turn 90 degrees. First position the number 1 cylinder to top dead center (TDC) position where the Crankshaft keyway matches the engine block mark while the idler sprocket arrow rises upward along with the guide pins of the Camshaft sprockets properly fitting the Cylinder Head notches. Remove the Camshaft timing chain tension by turning the intake Camshaft gently counter-clockwise before taking out the nut and 2 bolts (1, 2). To avoid crank or cam motion after tensioner removal remove the Camshaft Timing Chain Tensioner and its gasket. Use a wrench to support the Camshaft before removing sprocket bolts followed by sprockets and chain. A thorough inspection of all Camshaft timing upper guide, tensioner, tensioner gasket and sprockets and chain components must be performed for wear and damage. Also replace any components which show excessive wear or damage. When installing the components verify that the Crankshaft keyway faces the engine block mark while the idler sprocket arrow points upward and the Camshaft guide pins fit the notches of the Cylinder Head. Line up the yellow link of the Camshaft timing chain against the arrow on the idler sprocket and the dark blue link with the arrows (2, 3) on the Camshaft sprockets. Position the Camshaft timing chain and its sprockets and torques the Camshaft sprocket bolts to 80 nm (58 ft. Lbs.). Install and tighten the Camshaft Timing Chain Tensioner by compressing the plunger body through its retainer before installing the gasket on top. Tighten the tensioner bolts to 11 nm (97 inch lbs.) with the retaining nut set to 45 nm (33 ft. Lbs.). Turn the Crankshaft 2 revolutions to bring its keyway into line with the engine block timing mark and verify Camshaft guide pins match up with the Cylinder Head notches. Before installation, add engine oil to the timing chains with tensioner, guides, sprockets and spark plugs. Affix the spark plugs with 25 nm (18 ft. Lbs.) torque. After completing, return the negative Battery Cable along with placing the timing chain housing into position.