Measuring gaps using a calibrated plastic rod Plastigage
To measure the clearance in the crankshaft connecting rod bearings, it is necessary to use a calibrated plastic Plastigage rod.
Apply marks (1) to determine the relative positions of the connecting rod and connecting rod cap.
Remove the bolts and cover and connecting rod bearing shell. Clean the bearing, cover and crankshaft journal.
Cut a piece of Plastigage plastic gauge rod the same length as the bearing width and place it along the crankshaft axis on the connecting rod bearing journal.
Install the connecting rod bearing cap with the liner and secure it with bolts, tightening them to a torque of 54 N·m.
Warning! Do not turn the crankshaft.
Loosen the bolts and remove the connecting rod bearing cap again. Compare the width of the deformed Plastigage plastic rod with the measuring scale printed on the plastic rod packaging. Use the scale to determine the gap.
If the gap exceeds 0.08 mm, check the crankshaft journal diameter. If the crankshaft journal diameter is within specification, replace the crankshaft connecting rod bearing shells as a set.
Install the connecting rod caps onto the connecting rods and secure with new bolts, tightening them to a torque of 54 N·m.
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Measuring clearances using a bore gauge and micrometer
Note: To measure connecting rod bearing clearances using a bore gauge and micrometer, the crankshaft must be removed from the engine.
Install the connecting rod bearing shells into the connecting rod and connecting rod cap.
Install the connecting rod cap onto the connecting rod and secure with bolts, tightening them to a torque of 54 N·m. When checking the clearances in the connecting rod bearings, the connecting rod cap mounting bolts can be used multiple times.
Using a bore gauge, measure the inside diameter of the crankshaft connecting rod bearing.
Calculate the average diameter of the connecting rod bearing bore using the formula:
Average diameter of connecting rod bearing bore = (I + II + III): 3
Using a micrometer, measure the diameter of the crankshaft connecting rod journal in two diametrically perpendicular planes.
Calculate the average diameter of the crankshaft journal using the formula:
Average diameter of crankshaft journal = (I + II): 2
Calculate the clearance in the crankshaft connecting rod bearing by subtracting the average diameter of the crankshaft connecting rod journal from the average diameter of the connecting rod bearing bore.
- Permissible taper of the crankshaft connecting rod journal: 0.005 mm
- Permissible clearance in the crankshaft connecting rod bearing: 0.08 mm.
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