Oil Valve Seals
Different manufacturers use different types of valve seals on their cylinder heads. Aluminum heads typically have positive lock valve seals. These are the preferred seal these days. They're installed prior to the valve and an installation tool is required. This is because these seals snap into place onto a machined groove on the head. Check the manual; intake and exhaust valves are typically different colors and sizes.
Another popular seal is the umbrella type valve seal. These valve seals used to be everywhere. They were used on all different types of engines. They’re installed after the valve has been placed in its guide. Polish the valve with crocus cloth and lubricate it with oil or assembly lube before installation.
O-ring seals are located on the valve stem in the third groove down, under the two retainer grooves. They're installed after the valve spring has been compressed. It's important to lubricate the seal with oil before sliding it over the valve stem.
Valve Seal Symptoms: When valve seals leak, oil enters the combustion chamber causing the vehicle to emit blue-gray smoke from its tailpipe. This is most apparent at start up, after the vehicle's been sitting for a while. This is because the oil on top of the cylinder head has had time to seep into the chamber. Once this oil has cleared out, the smoke may not be so apparent until this process is repeated again.