Q: What tools and compressed air source are required to replace broken valve springs and defective valve stem seals without removing the cylinder heads on 2.4L four cylinder Nissan Frontier?
A: To do this, you will need a compressed air system and special tools. After removing the valve cover and top Timing Chain, camshaft and lifters should be removed from affected cylinder head. In case you plan to replace all the valve stem seals, remove all spark plugs. Put the piston of the bad-cylinder at TDC in its compression stroke by turning the crankshaft. Place an adapter into the spark plug hole and use compressed air on that cylinder. For protection against debris entering the engine, fill with old rags around each valve. Use a spring compressor to compress spring and remove valve stem keepers. Pay attention to any bending or misalignment of the valve stem. Replace valve stem seals, lubricate valve stems then reinstall valve springs, retainers and keepers. Take off compressed air then reset camshaft, lifters, timing chain, valve cover then spark plugs and plug wires. Finally start as well as run an engine; check oil leaks and abnormal valves covers sounds.