Connecting Rod Bearing Clearance, Plastigauge Method - Mercury MerCruiser Service Manual

Engine Inspection and Assembly
IMPORTANT: Do not measure inside diameter close to the connecting rod and bearing split line.
a
6. Record the measurements.
7. Wipe the crankshaft connecting rod journal with a clean cloth. Remove any oil film.
8. Measure the crankshaft connecting rod journal diameter with a micrometer. Take a second measurement at a position on
the connecting rod journal at a point 90° from the first measurement.
b
a
b
Description
Diameter
Taper
Out of round
Inadequate clearance or interference between the bearing and its mating surface will result in rapid bearing wear and
catastrophic component failure. Check all bearing clearances.
9. If the crankshaft rod bearing journal diameters are not within specifications, replace or recondition the crankshaft.
10. If the crankshaft rod bearing journal diameters are within specifications, determine bearing clearance by subtracting the
crankshaft connecting rod journal outer diameter from the inner diameter of the bearing from step 5.
Description
Clearance
11. If the clearance exceeds specifications, select a new, correct size bearing, and recheck the bearing clearance.

Connecting Rod Bearing Clearance, Plastigauge Method

The plastic gauge method is an optional method of determining connecting rod bearing clearance. Micrometer measurement is
the preferred method.
1. Wipe both upper and lower bearings and the crankshaft connecting rod journal with a clean soft cloth. Remove any oil film.
2. Install the bearings in the connecting rod and cap.
IMPORTANT: To obtain accurate measurements the connecting rod and upper bearing must be seated against the
connecting rod journal before installing the lower bearing and rod cap.
3. Rotate the crankshaft or move the connecting rod until the upper bearing is fully seated against the connecting rod journal
being measured.
Page 3B-30
a - Inside dial indicator
b - Assembled rod and bearings
c - Split line
b
c
30340
a
© 2016 Mercury Marine
53.3095–53.3295 mm (2.0988–2.0995 in.)
Production
Production
NOTICE
Production
a - Measurement point "a"
b - Measurement point "b"
30347
6.2 Liter (377 cid)
0.005 mm (0.0002 in.) maximum
0.008 mm (0.0003 in.) maximum
6.2 Liter (377 cid)
0.047–0.110 mm (0.0019–0.0043 in.)
90-8M0099748 eng DECEMBER 2015