The process of installing valves is the same regardless of the type of cylinder head. The cylinder head should be checked for cracks, valve seats, valve guides, warpage and valve spring installed height before replacing the valves. The valve train sustains a larger amount of wear than any other part of the engine. In most cases, however, the valve seats and the valve springs are the most likely to show wear.
Lay the cylinder head on a clean bench.
Remove the cam shafts should the cylinder head be off of a overhead cam engine. If it is a single cam, remove the cam bearing caps starting in the middle and moving outward. Use a socket and ratchet to loosen the cap bolts, and make sure to keep the caps oriented to the same mating surface. Once the caps are removed, lift the camshaft off of the head and set it flat on the bench. Replace the caps in their original position and loosely install the bolts. Do the same thing for a twin cam head, except mark the camshafts as "intake" or "exhaust" prior to removing.
Install the valve spring compressor. The compressor is a large C-clamp with a round foot on the bottom for the valve face, and the top has a round foot with a hole in the centre for the valve stem. Install the compressor with the bottom foot squarely on the face of the valve. Put the top round foot over the top of the valve spring. Make sure the hole in the centre of the foot is over the valve stem in the centre of the spring. Push the handle down. This will compress the valve spring down below the keepers. Use the magnet to remove the keepers from the valve stem. Lift the handle up and release the pressure on the valve and remove the compressor.
Compress the valve springs with the valve spring compressor and remove the valves. The springs are held in a compressed state on the valve by a set of keepers. The valve has a recess cut out of the valve stem close to the top of the stem. These recesses are designed for a set of conical, semicircular, tapered pieces. When these two halves are put together, they look like a funnel. The valve spring has a cap on top called a retainer. It has a tapered hole in the centre. When the spring is compressed and the tapered keepers are installed on the upper part of the valve stem and then the spring pressure released, as it expands upward, the keepers slide into the tapered hole in the spring retainer. The keepers will not allow the spring to pass, so the spring pressure pushes the valve closed.
Lift the spring off of the head and over the valve stem. These springs must go on the same cylinder from which they were removed. Mark or place them in order so this can be done.
Rotate the head over and remove the valve. Inspect the valve seat for uneven wear or cracks. Check the valve for cracks. If the seat of the valve is cracked, take the head to a machine shop for repair. If there are no cracks, rotate the head again so that it is right side up. Turn the valve that was just removed upside down with the stem down. Insert the stem into the valve guide and try to rock the valve side-to-side. If there is any amount of movement, the valve guide is worn and will cause the valve to seat improperly, leak and cause oil burning, so it will need to be replaced. Take the valve out and look down into the valve guide. The hole should be perfectly round.
Push the new valve through the bottom of the head. Put the bottom of the spring compressor on the face of the valve. Install a new valve seal over the valve stem and push it down the stem until it just contacts the valve guide. This keeps oil from running down the valve stem and on top of the valve. Without these, the engine will smoke.
Place the valve spring over the valve stem and put the retainer on top of the valve spring. Put the compressor top foot over the spring and push the handle down to compress the spring. Place the keepers on the valve stem and hold them in place with the tips of your fingers.
Lift the handle on the compressor (very slowly) to release the pressure. As the spring rises, when the keepers are starting to enter the hole in the retainer, let go of the keepers and release the rest of the pressure on the spring. Make sure the keepers are level and inside the spring keeper. Do the same for all the valves.