3A-20 - ENGINES 90-823225--1 1096
Piston Failures
Pre-Ignition
Pre-ignition is abnormal fuel ignition, caused by com-
bustion chamber hot spots. Control of the start of igni-
tion is lost, as combustion pressure rises too early,
causing power loss and rough running. The upward
motion on the piston is opposed by the pressure rise.
This can result in extensive damage to the internal
parts from the high increase in combustion chamber
temperature.
72424
Pre-Ignition Damage
PRE-IGNITION CAUSES
1. Hot spots in the combustion chamber from glow-
ing deposits (due in turn to the use of improper
oils and/or fuels).
2. Overheated spark plug electrodes (improper
heat range or defective plug).
3. Any other protuberance in the combustion cham-
ber, such as an overhanging piece of gasket, an
improperly seated valve or any other inade-
quately cooled section of material which can
serve as a source.
1
2
3
4
Engine failures, which result from the foregoing con-
ditions, are beyond the control of Mercury Marine;
therefore, no warranty will apply to failures which oc-
cur under these conditions.
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