To do this you will need to remove the valve covers from the cylinder heads and the bolts that hold the rocker arm shafts in place and these bolts are the center bolts followed by the bolts at the extremity of the rocker arm shafts. After the last nut is fully loosened, carefully lift the rocker shaft assembly off of the cylinder head, being sure note the position betwen the upper intake and lower exhaust rocker arms so that they can be reassembled in their original orientation. Rocker arm positions should be recorded in order to reinstall them in the correct position; each set of components should be replaced and stored as they were found; and the pushrods should be removed and stored in an order to avoid crossing them up. It is important for one to note that exhaust pushrods are a little longer than intake pushrods not interchangeable. If the cylinder heads have been machined to a standard of flatness then it is crucial to 'shorten' the appropriate length pushrods to cover the now shorter distances of the rocker arms to the
Camshaft dimensions, unless consulting with a machine shop. For each rocker arm, check if there is wear, cracks, and damage on the surface that comes into contact with pushrods and or valve stems, and the rocker arm shafts and the bores should also be checked to establish if they have worn out and or damaged, a worn out or damaged part must be replaced. There must be free passage into the hole at the pushrod end of each rocker arm; bears checking for crackline and abnormal wear, pushrods can be rolled across a flat surface to check for bend. Coat the lower end of each pushrod with clean engine oil or assembly lube and install these into their original position and ensure that it seals fully into the lifter socket. Coat the valve stems and the upper ends of the pushrods with assembly lube for protection of any mating surfaces during initial start up, then lubricate the rocker shafts, the rocker shaft assembly should have all components located in their original positions before being installed in to the head of the cylinder. Tighten the rocker arm shafts beginning with the centre bolt, in a preset sequence till the appropriate torque is secured so that the pushrods fit tightly in the rocker arms. If bolts when installed appear light before the shaft is seated or if pushrods bind, all the components inside should be examined. Last, put the valve covers back on, crank up the engine, scan for valve train rattles and knock and look for oil leaks at the gaskets.