We work on a cold engine.
Use spark plugs recommended by the manufacturer: CHAMPION RN9YC, NGK BPR6ES or equivalents from other manufacturers.
To replace the spark plug..
... remove the tip of the high-voltage wire from the candle.
With a high "21" head with an extension cord or a candle wrench, we unscrew the spark plug..
...and take it out.
We check the gap between the electrodes of the candle with a round probe.
If the clearance is not correct (0.7–0.8 mm), carefully bend the side electrode, achieving the required gap.
When screwing in the spark plug, turn the socket extension or spark plug wrench by hand, not with a wrench or ratchet, to avoid damage to the threads of the spark plug hole in the cylinder head.
If the candle has not gone along the thread, there will be a strong resistance to rotation. In this case, it is necessary to completely unscrew the candle and, having cleaned the thread, re-wrap it.
Finally tighten the spark plug to 25 Nm.
Similarly, we check (replace) other spark plugs.
Overtightening the spark plugs can damage the threads in the spark plug holes in the cylinder head.