See Figures 1, 2 and 3
REMOVAL AND INSTALLATION
- Block the head on its side, or install a pair of head-holding brackets made especially for valve removal.
- Use a socket slightly larger than the valve stem and keepers, place the socket over the valve stem and gently hit the socket with a plastic hammer to break loose any varnish buildup.
- Remove the valve keepers, retainer, spring shield and valve spring using a valve spring compressor (the locking C-clamp type is the easiest kind to use).
- Keep all parts organized in a separate container numbered for the cylinder being worked on; do not mix them with other parts removed.
- Remove and discard the valve stem oil seals. A new seal will be used at assembly time.
- Remove the valves from the cylinder head and place them, in order, through numbered holes punched in a stiff piece of cardboard or wood valve holding stick.
The exhaust valve stems, on some engines, are equipped with small metal caps. Take care not to lose the caps. Make sure to reinstall them at assembly time. Replace any caps that are worn.
- Use an electric drill and rotary wire brush to clean the intake and exhaust valve ports, combustion chamber and valve seats. In some cases, the carbon will need to be chipped away. Use a blunt pointed drift for carbon chipping. Be careful around the valve seat areas.
- Use a wire valve guide cleaning brush and safe solvent to clean the valve guides.
- Clean the valves with a revolving wires brush. Heavy carbon deposits may be removed with the blunt drift.
When using a wire brush to clean carbon on the valve ports, valves etc., be sure that the deposits are actually removed, rather than burnished.
- Wash and clean all valve springs, keepers, retaining caps etc., in safe solvent.
- Clean the head with a brush and some safe solvent and wipe dry.
- Check the head for cracks. Cracks in the cylinder head usually start around an exhaust valve seat because it is the hottest part of the combustion chamber. If a crack is suspected but cannot be detected visually have the area checked with dye penetrant or other method by the machine shop.
- After all cylinder head parts are reasonably clean, check the valve stem-to-guide clearance. If a dial indicator is not on hand, a visual inspection can give you a fairly good idea if the guide, valve stem or both are worn.
- Insert the valve into the guide until slightly away from the valve seat. Wiggle the valve sideways. A small amount of wobble is normal, excessive wobble means a worn guide or valve stem. If a dial indicator is on hand, mount the indicator so that the stem of the valve is at 90° to the valve stem, as close to the valve guide as possible. Move the valve off the seat, and measure the valve guide-to-stem clearance by rocking the stem back and forth to actuate the dial indicator. Measure the valve stem using a micrometer and compare to specifications to determine whether stem or guide wear is causing excessive clearance.
- The valve guide, if worn, must be repaired before the valve seats can be resurfaced. Manufacturers supply valves with oversize stems to fit valve guides that are reamed to oversize for repair. The machine shop will be able to handle the guide reaming for you. In some cases, if the guide is not too badly worn, knurling may be all that is required.
- Reface, or have the valves and valve seats refaced. The valve seats should be a true 45° angle. Remove only enough material to clean up any pits or grooves. Be sure the valve seat is not too wide or narrow. Use a 60° grinding wheel to remove material from the bottom of the seat for raising and a 30° grinding wheel to remove material from the top of the seat to narrow.
- After the valves are refaced by machine, hand lap them to the valve seat. Clean the grinding compound off and check the position of face-to-seat contact. Contact should be close to the center of the valve face. If contact is close to the top edge of the valve, narrow the seat; if too close to the bottom edge, raise the seat.
- Valves should be refaced to a true angle of 44°. Remove only enough metal to clean up the valve face or to correct runout. If the edge of a valve head, after machining, is 1/32inch (0.8mm) or less replace the valve. The tip of the valve stem should also be dressed on the valve grinding machine, however, do not remove more than 0.010inch (0.254mm).
- After all valve and valve seats have been machined, check the remaining valve train parts (springs, retainers, keepers, etc.) for wear. Check the valve springs for straightness and tension.
- Install the valves in the cylinder head and metal caps.
- Install new valve stem oil seals.
- Install the valve keepers, retainer, spring shield and valve spring using a valve spring compressor (the locking C-clamp type is the easiest kind to use).
- Check the valve spring installed height, shim or replace as necessary.
See Figures 4 and 5
Place the spring on a flat surface next to a square. Measure the height of the spring, and rotate it against the edge of the square to measure distortion. If spring height varies (by comparison) by more than 1 / 16 inch or if distortion exceeds 1 / 16 inch, replace the spring.
In addition to evaluating the spring as above, test the spring pressure at the installed and compressed (installed height minus valve lift) height using a valve spring tester. Springs used on small displacement engines (up to 3 liters) should be plus or minus1 lb. of all other springs in either position. A tolerance of plus or minus5 lbs is permissible on larger engines.
VALVE SPRING INSTALLED HEIGHT
See Figure 6
After installing the valve spring, measure the distance between the spring mounting pad and the lower edge of the spring retainer. Compare the measurement to specifications. If the installed height is incorrect, add shim washers between the spring mounting pad and the spring. Use only washers designed for valve springs, available at most parts houses.
VALVE STEM OIL SEALS
When installing valve stem oil seals, ensure that a small amount of oil is able to pass the seal to lubricate the valve stems and guide walls, otherwise, excessive wear will occur.
The stem seals used on the 5.0L (VIN Y) engine are color coded; the GREY seal is for the intake valve and the IVORY seal is for the exhaust valve.