Every 15,000 km, it is recommended to replace the spark plugs with new ones.
Before installing new spark plugs, check the gap between the spark plug electrodes, which should be within 0.6 mm. It can only be adjusted by bending the side electrode.
It is allowed to unscrew the spark plugs from the cylinder head only with a special key.
Before installing spark plugs, lubricate their threaded part with a thin layer of graphite grease.