To replace failed valve springs and leaking valve seals without cylinder head removal, carry out the following steps meticulously. Start with removing the upper and lower intake plenum, as well as the valve covers, then move ahead to timing chain,
Camshafts and lifters from both cylinder heads disassembly. Remove spark plugs and turn the crankshaft until piston on affected cylinder reaches top dead center (TDC) on compression stroke doing one cylinder at a time in firing order sequence. Screw a long adapter into spark plug hole, connect an air hose from compressed air source to pressurize the cylinder. To prevent losing parts inside engine place shop rags in holes of the cylinder head around valves and then use valve spring compressor to compress spring freeing valve stem keepers. Take out keepers; check for damage on a valve stem and if it binds. Reapply air pressure to hold the valve closed, release any temporary restraints, lubricate oil engine into valve stems and using a special tool or deep socket with hammer install new seals of the stem for valves. Install valve spring, retainer and keepers ensuring that they are correctly positioned then remove compressor spring. Remove this hosepipe then fix back spark plug adapter after which you will finally proceed to putting camshaft lifters timing chain covers other than going down through spark plugs ignition coils upper lower intake plenum. Eventually begin engine running checking for oil leaks and any abnormal sounds from the vicinity of cover over valve areas.