Spark-Plugs; Sacrificial Anode - SELVA MARINE MADEIRA 40 Owner's Manual

Spark-plugs

The spark-plug must be often inspected because heat and deposits affect
its efficiency so that the performance of the motor will be affected too.
The inspection of the spark-plug must be done when the engine
is not running and it has cooled down.
It is very important to check, that the part made of porcelain is
not damaged because this could allow external sparks, which
could lead to explosion or fire.
To remove the spark-plug use the supplied spanner; using an abrasive
brush, remove any depots, then check the wear condition and the spark-
plug gap ( the gap must be 0,6 mm, to measure it use a thickness gauge )
If the spark-plug is badly worn you must replace it with a new one which
must agree with the characteristics listed in the specifications chart.
The spark-plug torque is 20 Nm ( ~ 2. kgm). If a torque-wrench
is not available, you can obtain a good estimate of the correct
torque turning the spark-plug completely by hand and then
turning it with the spanner, a new spark-plug must be turned ~
90° and an old one 15° ÷ 20°.
Replace the spark-plug cap, checking that it is correctly fitted and then
replace the top cowling.

Sacrificial anode.

To protect the motor against electrochemical corrosion, due to the
presence in its structure of many different materials, a sacrificial anode
has been applied.
The anode will be subject to a strong corrosion, so you have to remove the
scales from the surfaces of the anode periodically.
When the corrosion compromise its functionality, you have to replace it.
Picture No.64
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Failure to clean it, will affect its effectiveness.
Do not paint the anode, for this would render it ineffective.
Picture No. 65