Preliminary Inspection; Piston Inspection - Mercury MerCruiser Service Manual

Engine Inspection and Assembly
3. Measure the clearance at the front end of the rear main bearing with a feeler gauge as shown.
Description
End play (thrust clearance)

Preliminary Inspection

IMPORTANT: All measurements should be taken when components are at room temperature.
1. Connecting rod
a. Check for twisted or bent connecting rods.
b. Inspect for nicks and cracks.
c. Inspect for damage to the bearing cap or bolt threads.
d. Replace damaged connecting rods.
2. Connecting rod bearings
NOTE: Refer to Main Bearing Inspection for examples of common bearing failures.
a. Inspect the connecting rod bearings for craters, pockets, or flattened sections.
b. Inspect the connecting rod bearings for excessive scoring, discoloration, or damage.
c. Inspect the connecting rod bearings for dirt or debris embedded in the bearing material.
d. Replace damaged or faulty bearings.

Piston Inspection

NOTE: Cylinder bore and taper must be within specifications before pistons can be considered for reuse.
1. Inspect the piston for cracked ring lands, skirts and pin bosses, wavy or worn ring lands, scuffed or damaged skirts, and
eroded areas at the top of the piston.
2. Inspect the ring grooves for nicks and burrs that may cause the rings to bind.
3. Inspect the piston for wear by checking the piston to bore clearance:
a. Measure the piston diameter 12 mm (0.472 in.) from the bottom of the skirt at a right angle to the piston pin bore as
shown.
b
b.
Measure the cylinder bore diameter with a telescope gauge. Refer to Piston Selection.
c. Subtract the piston diameter from the cylinder bore diameter to determine piston to bore clearance.
d.
Replace the piston if the piston to bore clearance is less than specified. Refer to Piston Selection for cylinder
reconditioning and piston replacement.
Page 3B-22
Measuring crankshaft end play
a
Measuring piston diameter
a - Piston diameter
b - Measurement location
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© 2016 Mercury Marine
19553
6.2 Liter (377 cid)
0.025–0.305 mm (0.001–0.012 in.)
90-8M0099748 eng DECEMBER 2015