When the engine cylinder head is on the block, take the engine cylinder head cover off, then the cap screws, bridge and pivot assemblies and rocker arms to work on each valve spring. Do not remove or reposition the push rods, bridges, pivots or rocker arms. Look for any issues or weaknesses in the spring and retainer and after that, remove the spark plug(s) right next to the valve spring. Attach a 14 mm air hose adaptor in the spark plug hole, link it with an air hose and make sure the pressure on air is 621 kPa to keep the valves on their seats. Use a rubber air connector when servicing the Number 1 cylinder in vehicles with an air conditioner. Hit the retainer or tip with a rawhide hammer, then compress the spring with the Valve Spring Compressor Tool MD-998772A and pull out the locks. After taking out the valve spring and retainer, then remove the valve stem seals, remembering not to mingle the INT seals (black) and the EXH seals (brown). Check the valve stems and, using an Arkansas smooth stone, lower any raised areas or get rid of nicks. Take care when installing the seals to avoid their damage from the rough sides of the valve spring lock groove, then press the valve seal slightly around the top of the valve stem and valve guide boss to make sure it is fitted correctly. Set the valve spring and retainer in place, squeeze the spring against the Valve Spring Compressor Tool MD-998772A, add the valve locks, release the spring, remove the tool and lightly tap the spring on its sides to check if it is seated. Air down the tire, disconnect the hose, pull out the adaptor and slot in the spark plug. Do the same steps on each spring within the valve train. Afterward, fit the push rods, so the bottom of each rod is at the center of the plunger cap seat in its respective hydraulic valve tappet and then replace the rocker arms, pivots and bridge at their original places. Follow a pattern when tightening the bridge cap screws, use a torque of 28 Nm and place the cylinder head cover.