To do this one has to slot the pushrod retainer special tool #9070 on the pushrods then bolt and tighten the tool mounting bolts. Un Tighten the rocker arm shaft bolts, from the middle then loosen the rocker shaft till you can lift it off the cylinder head, the heads of the rocker arm assembly are marked to indicate that the upper are intakes and the lower exhausts. Since the tangs may fall into the engine if removed, it is necessary not to take out the retainers from the rocker shaft assemblies. Make sure of the positions of the rocker arms in order to align them for reassembly, and store every set of rocker parts properly. Now, one by one undo the pushrod retainer tool fasteners and take out the pushrods, while pulling back the trolley as required in order not to mix the exhaust pushrods with the intake ones, as the former are slightly longer than the latter and, therefore, are not interchangeable. Where the cylinder heads have been removed and milled to ensure flatness, ensure to replace the correct length of pushrods to match the dimension of the decrease distances for the rocker arms to the camshaft. Examining each rocker arm on wear, cracks, and other damages, at the contact points with the pushrods and the valve stems, as well as the rocker arm shafts and bores for wears, and replace the worn or damaged one. Assure that there is an open hole at the pushrod end of each rocker arm and if possible look for cracks on the push rods, and excessive wear, roll each of the push rods across a piece of plate glass. Coat the lower end of each pushrod using clean engine oil or assembly lube and then replace these in their original spots; make sure it settles correctly and firmly within the lifter socket. Use engine assembly lube on the ends of the valve stems and at the upper end of the push rods in view of the initial starting period. Following the realignment of the pushrods, fix the pushrod retainer nuts as tightly as possible. Coat the rocker shafts with clean engine oil or assembly lube, then fit the rocker shafts with all parts as they have been before and then put them back on the cylinder heads. Tighten the rocker arm shafts firstly on the centre bolt and in sequence on opposite ends until the right torque is attained to sit the pushrods correctly in the rocker arms. If the rocker arm bolts tighten further before the shaft settles or if the push rods stick, one should not carry on tightening as this will only aggravate the problem; he or she should remove the rocker arm and then examine the rocker arm shafts and other components closely. Last, remove the pushrod retainer and the special tool, replace the valve covers and start the engine, preliminary checking for the strong valve train squealing and the oil leakage on the valve cover gaskets.