GMC 12612839 Sprocket Asm,Timing Chain Idler (LH)

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Caution! This is a complex process with an possibility of causing serious engine damage if not done correctly. Without significant experience in this kind of repair, do not try to replace the timing chain; unless you are sure about it, consult a specialist. Before attempting to start the engine, ensure accuracy through double-checking all work. Make sure that all sprockets have timing marks before removing the timing chain(s) from their sprockets. These tools required for this procedure (EN 48383-1, 48383-2, and EN 48383-3) can be obtained from SPX Tools. The following steps outlined below must assume that we have already got rid of the engine, subframe and transaxle assembly, right? Begin by disconnecting the battery ground cable negative terminal, drain oil out of the car and remove oil filter. Remove spark plugs for easier engine rotation; drivebelt and tensioner; intake manifold; valve covers; water pump; power steering components without disconnecting lines; alternator; crankshaft pulley; Camshaft Position (CMP) sensors; camshaft position actuator valves; engine mount bracket; drivebelt idler pulley thermostat housing. Disconnect each corner bolt with a bolt close to the water pump to release cover from block at bottom end of engine cover and carefully separate from block tapping gently with soft mallet. Turn the crankshaft till primary timing chain sprocket mark aligns with oil pump housing mark at five o'clock position. Engage special tools onto camshafts remove rear cylinder head timing chain tensioner bolts and cautiously take off tensioner. Release special holding tools off cams (camshafts). Repeat this process for lower or primary timing chain on front cylinder head. Clean components replacing as necessary and reset tensioners. Installation with crankshaft sprocket aligned with woodruff key ensuring timing marks are aligned as well as special tools on the camshafts. Mount timing chains, guides and tensioners ensuring accurate positioning of all timing marks, remove camshaft retaining tools. Rotate crankshaft till sprocket mark align with oil pump housing mark at 9 o'clock position; use special locking tools to lock up the cams (camshafts) and proceed to install the rear cylinder head timing chain. Insert inner and outer guides, a new tensioner gasket as well as the tensioner itself. Repeat this process for front cylinder head primary timing chain. Clean timing chain cover carefully, apply RTV sealant then slide over crankshaft using aligning studs before tightening cover bolts. Reinstall everything in reverse but only check proper engine rotation before starting it.

Carefully clean the timing chain cover, apply RTV sealant, and slide it over the crankshaft, using aligning studs before tightening cover bolts.