Q: How to replace the Timing Chain and Variable Timing Sprocket in V6 engine on Pontiac Firebird?
A: Disconnect the cable from the negative battery terminal and remove the vibration damper. Next, take off the crankcase front cover. Before removing the chain and sprockets, visually inspect the teeth on the sprockets for signs of wear and check the chain for looseness, along with the condition of the timing chain tensioners. If either sprocket shows wear, such as non-square edges, bright or blue areas, chipping, or pitting, replace them. If the timing chain hasn't been replaced recently or if the engine has over 25,000 miles, it likely needs replacement to avoid erratic engine performance, loss of power, and reduced gas mileage. When one component requires replacement, all related components, including tensioners, should also be replaced. To replace timing components, rotate the crankshaft until the marks on the camshaft and crankshaft are aligned, ensuring the number one and four pistons are at top dead center with the number four piston in the firing position. Do not remove the sprockets or chain until this alignment is confirmed, and avoid turning the crankshaft or camshaft afterward. Remove the three camshaft sprocket retaining bolts and lift the camshaft sprocket and timing chain off the engine, using a soft-faced hammer if necessary. If the crankshaft sprocket needs removal, use a special puller. Attach the crankshaft sprocket to the crankshaft with a bolt and washer from the puller set. Lubricate the thrust surface of the camshaft sprocket with moly-based grease or engine assembly lube, then install the timing chain over the camshaft sprocket with slack hanging over the crankshaft sprocket. With the timing marks aligned, slip the chain over the crankshaft sprocket and draw the camshaft sprocket into place with the retaining bolts, avoiding any hammering that could dislodge the Welch plug. After ensuring the timing marks are properly aligned, lubricate the chain with engine oil and reinstall the remaining components in reverse order.