POWERHEAD
Page 4A-34 90-855347R1 JANUARY 1999
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 con-
necting 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(s) which resembles a
tiny washboard. In some instances, the connecting rod crank pin bore becomes highly
polished. During operation, the engine will emit a “whirr” and/or “chirp” sound when
it is accelerated rapidly from idle speed to approximately 1500 RPM, then quickly re-
turned to idle. If the preceding conditions are found, replace both the crankshaft and
connecting rod(s).
a
51853
a
a-Chatter Marks Between Arrows
7. Uneven Wear: Uneven wear could be caused by a bent connecting rod.
a
51853
a
a-Uneven Wear Between Arrows
8. If necessary, clean connecting rod bearing surfaces, as follows:
a. Be sure that “etched” marks on connecting rod (crankshaft end) are perfectly
aligned with “etched” marks on connecting rod cap. Tighten connecting rod cap
attaching bolts securely.
CAUTION
Crocus cloth MUST BE USED to clean bearing surface at crankshaft end of con-
necting rod. DO NOT use any other type of abrasive cloth.
b. Clean CRANKSHAFT END of connecting rod by using CROCUS CLOTH
placed in a slotted 3/8 in. (9.5 mm) diameter shaft, as shown. Chuck shaft in a drill
press and operation press at high speed while keeping connecting rod at a 90°
angle to slotted shaft.
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