Mercury 200 OptiMax Jet Drive Service Manual page 309

Powerhead
4. Check for water marks. When bearing surfaces are subjected to water contamination, a bearing surface etching occurs. This
etching resembles the size of the bearing.
5. Check for spalling. Spalling is the loss of bearing surface, resembling flaking or chipping. Spalling is most evident on the thrust
portion of the connecting rod in line with the "I" beam. General bearing surface deterioration could be caused or accelerated
by improper lubrication.
6. Check for chatter marks. Chatter marks are the result of a combination of low speed ‑ low load ‑ cold water temperature
operation, aggravated by inadequate lubrication or improper fuel. Under these conditions, the crankshaft journal is hammered
by the connecting rod. As ignition occurs in the cylinder, the piston pushes the connecting rod with tremendous 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 crankshaft then remains immobile for a split second until the piston travel causes the connecting rod
to catch up to the waiting crankshaft journal, then hammers it. The repetition of this action causes a rough bearing surface
which resembles a tiny washboard. In some instances, the connecting rod crankpin bore becomes highly polished. During
operation, the engine will emit a whir or chirp sound when it is accelerated rapidly from idle speed to approximately 1500
RPM, then quickly returned to idle. If the preceding conditions are found, replace both the crankshaft and connecting rods.
7. Check for uneven wear. Uneven wear could be caused by a bent connecting rod.
Page 4A-44
a
8690
a
8691
a
8692
a
8694
a - Water marks
a - Spalling
a - Chatter marks
a - Uneven wear
90-8M0050731 MAY 2011