Piston Damage Due To Detonation and/or Pre-Ignition

PISTON DAMAGE DUE TO DETONATION AND /OR PRE-IGNITION

WARRANTY NOTICE: Engine failure due to detonation and/or pre-ignition is not a defect in material or workmanship. Warranty coverage may not apply to these types of engine failures unless it is proved the failure was caused by a defective part.

Detonation, commonly called “spark knock” or “fuel knock,” is abnormal combustion of the fuel which causes the fuel to explode violently within the combustion chamber.

Normal burning or combustion in a four-cycle engine starts at the spark plug, and a wave of fl ame moves across the combustion chamber. This results in a smooth pressure rise in the combustion chamber which pushes the piston downward.

Detonation starts out as normal combustion with the spark-ignited fl ame progressing across the combustion chamber while applying heat and pressure to the unburned portion of fuel. Then, instead of continuing to burn smoothly and evenly, the last portion of fuel explodes violently, causing overheating of the spark plugs, pistons and valves.

Detonation can occur at any engine speed. It is often not detected because of normal operation noises and wellinsulated engine compartments. Undetected detonation may result in serious engine damage.

The use of low-octane gasoline is one of the most common causes of detonation. Even when using proper gasoline, detonation can occur if engine maintenance is neglected. Some other causes of detonation are: • Improper gasoline quality (octane - R.V.P.)

• Improper propeller selection (lugging engine - inability of engines to reach rated WOT RPM)

• Improper initial timing setting (power timing)

• Engine overheating. Improper cooling system operation resulting in overheating condition

• Fuel system vapor lock (poor fuel quality, lean fuel mixture)

• Improper carburetor function (water and/or dirt), (fl oat setting) causing lean mixture • Operating twin engine boat on one engine at high throttle setting resulting in overload.

• Operating engine with dead cylinder, out of proper tune or wired with improper fi ring order. Defective distributor cap (carbon tracked).

• Excessive exhaust back-pressure caused by restrictive muffl ers and/or collectors or undersized exhaust outlets.