Broken valve springs and defective valve stem seals can be replaced without removing the cylinder heads, typically requiring two special tools and a compressed air source. If the head remains on, a special on-vehicle valve spring compressor should be obtained, ensuring the correct spring compressor is available before starting. If special tools are unavailable, the heads must be removed to use a clamp-type valve spring compressor. Begin by removing the upper intake manifold and valve cover(s), followed by the timing chain, camshafts, and lifters from both cylinder heads. Remove the spark plugs and turn the crankshaft until the piston in the affected cylinder is at Top Dead Center. For replacing all valve stem seals, start with cylinder number one and work through the firing order, turning the crankshaft 120 degrees to bring the next cylinder to TDC. Thread a long adapter into the spark plug hole and connect an air hose from a compressed air source, using a long spark plug adapter with a hose attached. Apply compressed air to the cylinder and stuff shop rags into the cylinder head holes around the valves to prevent parts and tools from falling into the engine. Use a valve spring compressor to compress the spring, releasing the valve stem locks with small needle-nose pliers or a magnet. The valves should be held in place by air pressure; if they cannot hold air, the cylinder head should be removed for a valve job. Remove the spring retainer and valve spring, then the valve stem seal. Wrap a rubber band or tape around the top of the valve stem to prevent it from falling into the combustion chamber, then release the air pressure. Inspect the valve stem for damage, ensuring it doesn't bind in the guide; if it does, the cylinder head will need to be removed for repair. Reapply air pressure to retain the valve in the closed position, then remove the tape or rubber band. Lubricate the valve stems with engine oil and install the new valve stem seals, using a special tool or a deep socket and hammer to tap the seal until seated. Install the valve spring over the valve with the more closely-wound coils and paint mark toward the cylinder head, then install the valve spring retainer. Compress the valve springs and carefully position the valve stem locks in the groove, applying a small dab of grease to hold them in place. Remove the force from the spring tool and ensure the valve stem locks are seated, then disconnect the air hose and remove the adapter from the spark plug hole. After replacing all seals, position the crankshaft at TDC, install the camshafts and lifters, then the timing chain. Finally, install the valve covers, spark plugs, ignition coils, and the upper intake manifold, and start the engine, checking for oil leaks and unusual sounds from the valve cover area.
Posted by NissanPartsDeal Specialist 
