Honda 2006 RC51 Owner's Manual page 122

5. With the plug washers attached, thread
the spark plugs in by hand to prevent
cross-threading.
6. Tighten each spark plug:
If the old plug is good:
1/8 turn after it seats.
If installing a new plug, tighten it
twice to prevent loosening:
a) First, tighten the plug:
NGK: 3/4
DENSO: 1/2
b) Then loosen the plug.
c) Next, tighten the plug again:
1/8 turn after it seats.
turn after it seats.
turn after it seats.
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Improperly tightened spark plugs can
damage the engine. If a plug is too loose,
a piston may be damaged. If a plug is too
tight, the threads may be damaged.
7. Reinstall the spark plug caps. Take care
to avoid pinching any cables or wires.
8. Install the remaining parts in the reverse
order of removal.
Servicing Your Honda
Spark Plugs
115