If you received it from repair after valve maintenance, then the valves and related components are already installed in place, and if not, then:
Install the valve back in its original place.
Install the spring seat, spring oil seal and upper plate.
Valve mounting elements
1 - spring seat;
2 - oil seal (oil deflector cap);
3 - spring;
4 - top plate.
Install the fixture and compress the valve springs until the valve groove is visible.
Place crackers on the upper groove of the valve and release the springs by releasing the device.
Tap the valve plate with a rubber mallet to loosen the crackers.
Repeat the above procedure for all other valves. Be sure to install all components in their original places - do not mix them up!
Check the installed height of the valve springs using a special ruler or measuring device. If the head was repaired in a workshop, the installed height of the springs must correspond to the required value (however, check it again). The measurement is taken from the top of each spring seat to the bottom of the mount. If the height value does not correspond to the required one, additional washers must be installed.
Further assembly of the head is carried out in the reverse order.