GMC 12612838 Sprocket Asm,Timing Chain Idler (RH)

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,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.

Disconnect the cable from the negative terminal of the battery, then remove the air filter housing and the air intake duct. Drain the coolant and engine oil, followed by the removal of the drivebelt and unbolting the drivebelt tensioner. Next, take out the thermostat and the water pump pulley, followed by the crankshaft pulley. Attach an engine support fixture to the engine lifting eyes, then remove the passenger side engine mount and the mount support bracket from the front of the timing chain cover. Remove the lower drivebelt idler pulley, the oil pan, the left drivebelt idler pulley, and the engine mount bracket from the top of the timing chain cover. Proceed to remove the water pump, the thermostat bypass hose adapter, and detach the radiator outlet hose from the timing chain cover. Remove the timing chain cover-to-engine block bolts and separate the cover from the engine, tapping gently with a soft-face hammer if necessary. Temporarily install the crankshaft pulley bolt and turn the crankshaft to align the timing marks on the crankshaft and camshaft sprockets. Remove the camshaft sprocket bolt(s) without turning the camshaft, and use two large screwdrivers to carefully pry the camshaft sprocket off the camshaft dowel pin, slipping the timing chain and camshaft sprocket off the engine. The timing chain should be replaced if the engine has high mileage, shows visible damage, or if total free play exceeds one inch. Inspect the timing chain dampener plate for cracks and wear, and clean the timing chain and sprockets with solvent. Remove all traces of old gasket material and sealant from the cover and engine block, then install the dampener plate and tighten the bolts. If the camshaft has turned, position the dowel pin at 3 o'clock, mesh the timing chain with the camshaft sprocket, and engage it with the crankshaft sprocket, ensuring the timing marks are aligned. Install the camshaft sprocket bolt(s) and verify alignment with the dowel pin, then lubricate the chain, sprocket, and front of the crankshaft gear with clean engine oil. Apply RTV sealant to both sides of the new gasket, position it on the engine block, and attach the cover, tightening the bolts in a criss-cross pattern. Complete the installation in reverse order, add oil and coolant, start the engine, and check for leaks.

Remove the crankshaft pulley and rotate the crankshaft to bring the #1 cylinder to Top Dead Center (TDC) on the compression stroke, aligning the timing marks on the camshaft gears and crankshaft sprocket.

The timing system is complex, and severe engine damage can occur if mistakes are made. Therefore, this procedure should only be attempted by those with significant experience in such repairs. If unsure, consulting an expert is advised.

This procedure requires three special tools (EN 48383-1, 48383-2, and EN 48383-3), which are available through SPX Tools.

This procedure requires three special tools (EN 48383-1, 48383-2, and EN 48383-3), which are available through SPX Tools.

Install the camshaft sprocket bolt, lubricate the chain and sprocket, and remove the tensioner locking tool.