First, take out and examine rocker arms and pushrods after removing the valve covers from cylinder heads. So, get yourself special pushrod retainer tool #9070 or its equivalent to ensure that the pushrods remain in place. Go on gradually loosening the rocker arm shaft bolts off starting with center bolts towards end. To remove this fully, lift the entire rocker shaft assembly off the cylinder head keeping in mind that retainers must remain under bolt head. Therefore keep record of every rocker arm posture since it is required to put them back to their original position. The intake rockers are marked "I" so store each set of rocker components correspondingly. Remove and put away push rods to hold them onto their initial positions as they were before removal or disassembling for maintenance purposes. Nevertheless remember that exhaust push-rods are a little bit longer than intake ones and cannot be replaced between themselves . In addition check each rocker arm for wear, cracks or damage especially where they contact the pushrods and valve stems during inspection periods. Also check for wear, galling, stress cracks, or unusual wear patterns on rocker arm shafts and bores of the arms themselves. Replace any worn or damaged rocker arms and shafts immediately . Never attempt to take out these retainers unless it becomes necessary because they can break down into your engine system. If a retainer breaks defeat it from the rocker arm shaft prior to reassemblying then install rockers again when broken . The last thing is installing/fitting/inserting/lodging both ends of all (the) pushrods; lubricate these pieces , apply engine assembly lube to valve stem ends/upper end portion/surface of valve stem along with top end surfaces of push rods; lubricate the rockershaf and install/co-locate/place/push together again other parts including such as valves in each original position on each head in which case the shaft of rockers is assembled. Sequence and torque the rocker arm shaft bolts to specification at several steps taking care that push - rods are seated properly. Finally put on valve covers, start the engine, and check for any unusual noises from or oil leaks around O-rings.