GMC 12612838 Sprocket Asm,Timing Chain Idler (RH)

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First of all, unplug the negative cable and unbolt being the intake air resonator and the intake plenum. However, the following are the removal procedures; First, the drivebelt and the drivebelt tensioner must be removed, then, the water pump pulley mounting bolts have to be removed as well as the pulley. Counter-loosen all the bolts that are holding the power steering pump on the bracket and then remove the pump from the bracket. As far as timing belt is concerned the coupling and the belt has to be changed Pull out all the mounting fasteners of Timing Cover and pull the cover away from the engine. When working on the timing belt and sprockets do not turn the crankshaft or camshafts individually with the belt out of the system to avoid straining the valves. Make sure that you have the special tools called for on the job before proceeding. Take off the timing cover belt, crankshaft pulley and turn the crankshaft so that Cylinder #1 reaches Top Dead Center on the compression stroke that gets the meshing timing marks of the camshaft gears and crankshaft sprocket in one straight line. Place bolts to lock the crankshaft from any movement, insert other bolts between the camshaft gears and release the tension on the timing belt tensioner. Roll the idler pulley and the timing belt out, and do not twist them frequently or sharply. Check the timing belt for signs of wear or contamination and replace it if it reached the 60k, or any other appropriate time. For installation include aligning all the marks on the camshaft sprockets and the crankshaft sprocket, looping the timing belt around the said crankshaft sprocket and the other necessary pulleys. After the lower idler pulley has been fitted all marked will have to be aligned, and the tension of the timing belt set. Rotate the crankshaft to get some resistance to see some problem and confirm all the marks matching and tighten the timing cover. Some changes may be made to match the camshaft sprockets to the special tools and if the sprockets get out of alignment, change the upper idler pulley eccentric. An additional step is to make sure that the alignment and tension are appropriate, please complete the installation.

Setting and particularly re-timing of the timing system is a delicate process which might lead to rather severe damages of the car engine if something goes wrong, therefore this kind of repair should be attempted only by persons with fairly vast experience in such cases; as for the rest, it is highly recommendable to consult an expert. Firstly, pull the cable off the negative terminal of the battery as well as the spark plugs. Then you need to turn the valve cover, and then to pull it off, next, you need to drain the engine oil, and then the drivebelt and its tensioner, and at last the engine front cover must be removed. Turn the engine clockwise until the No. 1 piston is at the top of the exhaust stroke; align the keyway and markings on the camshaft sprockets. While turning your camshaft removed the timing chain tensioner, and the upper timing chain guide with the help of the exhaust camshaft sprocket bolt. Go forth and, eradicating the adjustable and fixed timing chain guides and then the intake camshaft sprocket bolt. Upon departure of the timing chain, do not rotate either of the camshafts or the crankshaft to prevent damaging the engine. , clean and check the condition of the chain tensioner, timing chain guides and sprockets and replace any that look suspicious. As described above, it is recommended that the experience driver should turn the crankshaft with his hand before starting the engine to feel some specific level of resistance to access the presence of some problems. Upon fitting of the timing chain, ensure that the given timing mark on the crank sprocket is in line and slot the intake camshaft sprocket and bolt it using a new bolt and tighten loosely. Place the timing chain in correct relative position of the colored links to the camshaft sprockets, then bolt in the adjustable and fixed timing chain tensioners, also the upper timing chain cover. The camshaft bolts should be tightly fastened with the camshafts held from turning which will provide enough looseness for installing the timing chain tensioner, which is in compressed position, and making sure that the tensioner assembly in well set. Replace the timing chain oiling nozzle and covering provide sealant on the access plug and replace the valvecove and engine front cover. Reverse all the steps you employed when carrying out the removal process, replace the oil filter, refill the crankcase with oil, reconnect the battery and start the engine and check for oil leaks.

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.

Rotate the crankshaft to align the sprocket mark with the oil pump housing mark in the 9 o'clock position, install special locking tools on camshafts, and proceed to install the rear cylinder head timing chain. Install inner and outer guides, a new gasket for the tensioner, and the tensioner itself. Repeat this process for the front cylinder head's primary timing chain.

Drain the coolant and engine oil.

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.

Inspect the timing chain dampener plate for cracks and wear.

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

The timing system is complex, and severe engine damage can occur from mistakes, so only highly experienced individuals should attempt this procedure. If unsure, consulting an expert is advised.