Chevrolet 12690246 Adjuster Assembly, Dual Feed Hyd Vlv Lash

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This is a difficult procedure, involving special tools. Read through the entire material and obtain the necessary tools before beginning. New camshaft sprocket bolts must be purchased for installation. Relieve the fuel system pressure. Disconnect the cable from the negative battery terminal. Remove the valve cover and high-pressure fuel pump. Remove the drive belt and drive belt tensioner. Set the engine to TDC. Remove the timing chain cover, the timing chain, and camshaft sprockets. Each camshaft cap should be marked for location and direction prior to disassembly. Loosen each bearing cap bolt slowly and evenly in reverse order of the tightening sequence. Lift the camshaft(s) from the cylinder head, parallel to the head surface. The caps must be installed in their original locations. Keep all parts from each camshaft together. Remove the rocker arms and place them in a suitable container, in order, for reinstallation. Remove the hydraulic lash adjusters from their bores in the cylinder head and store them with their corresponding rocker arms. Check each hydraulic lash adjuster for excessive wear, scoring, pitting, or an out-of-round condition. If the adjusters or the cylinder head bores are excessively worn, new adjusters or a new cylinder head, or both, may be required. Inspect the rocker arms for signs of wear or damage, particularly at the tip that contacts the valve stem, the socket that contacts the lash adjuster, and the roller that contacts the camshaft. Examine the camshaft lobes for scoring, pitting, galling, and evidence of overheating. Look for flaking of the hardened surface layer of each lobe. Measure the lobe height of each cam lobe on the intake camshaft and record your measurements. Compare the measurements for excessive variation; if the lobe heights vary more than 0.00 inch (0.125 mm), replace the camshaft. Inspect the camshaft bearing journals and the cylinder head bearing surfaces for pitting or excessive wear. Measure the diameter of each camshaft bearing journal at several points. If any journal is less than the specified minimum, replace the camshaft. Lubricate the rocker arms and hydraulic lash adjusters with engine assembly lubricant or fresh engine oil. Install the adjusters into their original bores, then install the rocker arms in their correct locations. Lubricate the camshaft(s) with camshaft installation lubricant or clean engine oil. With the camshaft notch at the front of the camshaft in the 12 o'clock position, install the camshaft into the cylinder head. Rotate the oil seal in the groove of the number one camshaft journal so the split line is at approximately the 12 o'clock position before installing the camshaft caps. Lubricate the camshaft bearing caps, then install the bearing caps into their original locations. Install the camshaft bearing cap bolts and hand-start the bolts. Tighten the bolts in sequence, a little at a time, to the torque. Install the camshaft actuator sprockets and timing chain, and the timing chain cover. The remainder of installation is the reverse of removal.

Removal involves removing the valve covers and the camshafts to remove the rockers is the lash adjuster socket on the rocker. Place markings on each rocker arm to ensure they are returned to the same position, then lift each one from the engine. Once the rocker arms are removed, the hydraulic lash adjusters can be lifted from the cylinder head. It is important that any rocker arms or lash adjusters being used again must be returned to their original position on the engine. Inspection involves checking each rocker arm for wear, cracks and other damage, especially where the valve stems contact the rocker arm. Check the rollers for binding and roughness. If the bearings are worn or damaged, replacement of the entire rocker arm will be necessary. Keep in mind that there is no valve adjustment on these engines, so excessive wear or damage in the valve train can easily result in excessive valve clearance, which in tum will cause valve noise when the engine is running. Make sure the oil passage hole in each hydraulic lash adjuster is not blocked. Installation involves applying some camshaft/lifter prelu be to the pivot pockets, roller and the slot that contacts the valve on each rocker arm. Apply clean engine oil into the bores for the hydraulic lash adjusters and install them into the cylinder head. Position the rocker arms onto the lash adjusters. The remainder of installation is the reverse of removal. Before starting and running the engine, change the oil and install a new oil filter.