How to replace a valve spring on a 2002 ford explorer sports trac
Remove valve covers. Buy tool to compress springs. Buy tool to introduce air into the cylinder through the spark plug hole. Buy a magnetic probe. Bring the piston you are working on up to the top of the stroke. Attach the air line and adaptor to the spark plug hole to pressurize the cylinder. Take a socket, place it on the spring retainer and give it a sharp whack. Use the spring compressor to compress the spring. Use the magnetic probe to remove the valve keepers and release the spring and retainer. Replace the spring, compress it, reinstall the retainer and keepers. Release the spring. Repeat for the other valves on that cylinder. Repeat the whole process on all the other cylinders and springs.
Have I scared you yet? Or have I adequately explained why your mechanic wants so much money to do this for you?