Mercury 225 EFI Service Manual page 366

POWERHEAD
4. Water Marks: When bearing surfaces are subjected to water contamination, a bearing
surface "etching" occurs. This etching resembles the size of the bearing.
5. Spalling: Spalling is the loss of bearing surface, and it resembles flaking or chipping.
Spalling will be most evident on the thrust portion of the connecting rod in line with the
"I" beam. General bearing surface deterioration could be caused by or accelerated by
improper lubrication.
6. Chatter Marks: Chatter marks are the result of a combination of low speed - low load
- cold water temperature operation, aggravated by inadequate lubrication and/or im-
proper fuel. Under these conditions, the crankshaft journal is hammered by the connect-
ing rod. As ignition occurs in the cylinder, the piston pushes the connecting rod with tre-
mendous force, and this force is transferred to the connecting rod journal. Since there
is little or no load on the crankshaft, it bounces away from the connecting rod. The crank-
shaft then remains immobile for a split second until the piston travel causes the connect-
ing rod to catch up to the waiting crankshaft journal, then hammers it. The repetition of
this action causes a rough bearing surface(s) which resembles a tiny washboard. In
some instances, the connecting rod crank pin bore becomes highly polished. During op-
eration, the engine will emit a "whirr" and/or "chirp" sound when it is accelerated rapidly
from idle speed to approximately 1500 RPM, then quickly returned to idle. If the preced-
ing conditions are found, replace both the crankshaft and connecting rod(s).
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90-884294 OCTOBER 2001