GM 12598504 Tensioner, Timing Chain

Tool required for this procedure is the special camshaft holding tool (part GM# J-44221 or equivalent). Start by rotating the crankshaft to set the engine to Top Dead Centre for cylinder number one, then unscrew the valve cover and the engine front cover. After collapsing the timing chain tensioner insert something like a drill bit or golf tee into the hole to keep the tensioner collapsed. The top chain guide can be removed by dismantling two bolts; next is the exhaust camshaft position actuator held by an Allen screw into a hex shape molded at the cam shaft while holding the camshaft still using a wrench. Then, take off the intake camshaft sprocket, relieve tension to the crankshaft sprocket and take off the chain while still holding the camshaft. Disconnect the two access hole plugs with a hex bit and the timing chain tensioner shoe bolt and the timing chain guide bolt, to pull out the guide and shoe and the tensioner, in case it is being replaced. The next step is to take out the crankshaft sprocket as is mentioned in the picture below. In case of his removal, the tensioner must be replaced and tightened to the optimum torque; the chain guide and the shoe must also be tightened with the bolts to the required torque. Screw in the two access plugs. Make sure cylinder one is still at Top Dead Centre, fit the camshaft holding tool making sure the lobes at the front of each camshaft are upright, the rear flats are upright. Insert crank sprocket and the chain must be fitted at angle on the intake sprocket on the marked dark link. Thread the chain over the cylinder head and over the crankshaft sprocket with the mark on the crankshaft sprocket lined up with a dark coloured link. Place the intake sprocket on the intake camshaft and it might become necessary to release a holding tool so as to slightly generate movement in the camshaft in other to align it before reengaging the holding tool. Raise the timing chain up and properly position the exhaust camshaft actuator over it; be sure that the mark on the absorber sprocket is over a dark coloured link before you install it to the exhaust camshaft permanently without heavily tightening the bolt. Once more, it can be just as necessary to wiggle the camshaft for proper positioning prior to reinstalling the holding tool. Turn the exhaust camshaft actuator clockwise until it cannot be turned further and set it in the position where the exhaust camshaft is fully advanced as failure to do this may cause severe problems to the engine. Retorque the intake camshaft sprocket bolt, respectively remove the drill bit or tee from the tensioner and withdrawal the camshaft holding tool. Last of all the timing mark should be aligned with the position where there are darkened links on the front of the intake camshaft sprocket, on the exhaust camshaft actuator and crank sprocket, then put all the parts back in as was done while removing them.

It is necessary to employ a special tool, camshaft holding tool, number GM# J-44221 or equivalent, for this operation. The timing system is a bit complicated and if a mistake is made during this process enormous damage to the engine can occur; therefore the work of this kind should be entrusted only to experienced personnel and it is mandatory to make sure twice of what has been done before starting the engine. Starting from TDC of cylinder number one the valve cover and the engine front cover should be unbolted; the word Delphi on the exhaust camshaft should be aligned with the valve cover mounting surface. Second, then, take off both the intake and the exhaust camshaft position sensors, then, the timing chain tensioner will then collapse thus requiring you to put a drill bit or a golf tee into position to keep it like that. Place the camshaft holding tool at the rear of the camshafts and then remove the top chain guide and the exhaust camshaft position actuator though holding the camshaft at the same time while undoing the bolt. Continue with the process of taking off the intake camshaft sprocket, disconnect the crankshaft sprocket from the camshaft chain, and then also take off the chain doing it while keeping the camshaft in a fixed position. Take out two access hole plugs from the front of the cylinder head, timing chain tensioner shoe bolt, timing chain guide bolt, after that take out the guide and shoe and the tensioner if they are being replaced. Take off the crankshaft sprocket, and prior to the startup of the engine, do the rotation of the crankshaft at least around two times and feel for any kind of load that signify an issue. When fitting the camshaft sprockets, fit new bolts and if disconnected, refit the tensioner and tighten to the indicated torque. Place the chain guide and shoe on the chain and tighten the bolts then fit the two holes with the access plugs. Before starting the engine, make sure that cylinder no.1 is again at TDC with the lobes of both Camshafts located at the front side of the Engine Head pointing upward with the Camshaft flats located at the back side also pointing upward. Fit the crank sprocket, still position the chain on the intake sprocket with one mark lined up with a dark link, thread the chain around the cylinder head through the crank sprocket ensuring the second mark is lined up. Bolt in the intake sprocket on the intake camshaft, and there might be a need to loosen and re-tightening of a holding tool for accurate alignment. Raise the timing chain up and manoeuvre the exhaust camshaft actuator over the correct sprocket so that a mark on the actuator is lined up with a dark link, then secure the actuator to the exhaust camshaft but do not over-tighten the bolt yet. Turn the exhaust camshaft actuator clockwise as far as it can be turned and make sure that the pointer is at the '0' mark before tightening the bolt. Loosen the intake camshaft sprocket bolt if it hasn't been done already and then use the drill bit or tee to turn the tensioner in and out Remove the camshaft holding tool. Lastly, align the timing mark and to finish the installation, reverse the whole procedure of removing number 4 cylinder head.

Install the camshaft holding tool at the rear of the camshafts.