Small-block engines use only one type of valve stem oil seal. The small-block seal is simply an O-ring which is installed on the lower groove of the valve stem and seals against the lower inside portion of the valve spring retainer.
Big-block engines have used four types of seals over the years. The first type is a rubber "umbrella" seal which is installed on the valve guide boss of the cylinder head and wipes the valve stem as the valve moves within the seal. The second type of seal is a nylon "umbrella" seal which is integral with the valve spring retainer. The third type is also nylon and is integral with the spring retainer, but is no longer serviced. If defective, the third type must be replaced with the second type. Both the second and third types seal against the top of the valve stem and divert any oil which may seep through. The fourth type is of the same design and arrangement as the small-block type.
REMOVAL & INSTALLATION
See Figures 1 and 2
The following Removal and Installation procedures apply to cylinder heads installed on the vehicle. Access to an air compressor and the purchase of certain special tools is required.
- Remove the valve cover (both of the covers if all of the springs and/or seals are to be replaced).
- Remove the spark plug from the cylinder which is to be serviced.
- Install an air line adaptor in place of the spark plug and attach the air line from the air compressor to the adaptor. The compressed air is used to hold the valves in place when the valve springs are compressed. If either of the valves of the cylinder to be serviced are open, attach the air line after step 4.
- Remove the rocker arm, ball and pushrod of the valve to be serviced.
- Install a special valve spring compressing tool to the rocker arm stud and retain the tool with the rocker arm nut.
- Lever the tool handle towards you to compress the spring. Remove the two valve locks (split keys) and release the pressure on the tool handle slowly. Remove the tool, valve spring, and related components.
If the valve does not stay in its uppermost position as the spring is compressed, the valve and/or valve seat are probably burned. A burned valve or seat will allow the compressed air to leak out of the cylinder. Cylinder head should be removed and overhauled.To install:
- If a rubber "umbrella" type seal is used (big-block only), install the seal over the valve stem and seat it onto the valve guide boss.
- Install the valve spring(s) and retainer over the valve and install the valve compressing tool. Compress the spring enough to expose the grooves of the valve stem.
On big-block models using the nylon seal, the seal must be attached to the retainer prior to installation.
- If O-ring type seals are used, position the O-ring into the lower groove of the valve stem, install the locks (retain with grease), and release the spring compressing tool. If the integral nylon seals are used, merely install the locks and release the spring compressing tool.
- Visually check that the locks are positioned properly in the retainer.
- Install the pushrod, rocker arm, and pivot ball. Tighten the rocker arm nut until it seems to be positioned the same as an undisturbed rocker nut.
- Disconnect the compressed air line, remove the air line adaptor, and reinstall and connect the spark plug.
- Adjust the valve as previously outlined and reinstall the valve cover(s).