Disassembly and Assembly
The serviceman must be very careful to use Plastigage
correctly. The following points must be remembered:
Make sure that the backs of the bearings and the
bores are clean and dry.
Make sure that the bearing locking tabs are properly
seated in their slots.
The crankshaft must be free of oil where the
Plastigage touches it.
If the main bearing clearances are checked with the
engine upright or on its side, the crankshaft must be
supported. Use a lack under an adjacent crankshaft
counterweight and hold the crankshaft against the crown
of the bearing. If the crankshaft is not supported, the
weight of the crankshaft will cause incorrect readings.
Put a piece of Plastigage on the crown of the bearing
half that is in the cap. Do not allow the Plastigage to
extend over the edge of the bearing.
Install the bearing cap using the correct torque-turn
specifications. Do not use an impact wrench. Be careful
not to dislodge the bearing when the cap is installed.
Do not turn the crankshaft with the Plastigage
Carefully remove the cap but do not remove the
Plastigage. Measure the width of the Plastigage while it
is in the bearing cap or on the crankshaft journal. Do this
by using the correct scale on the package. Record the
Remove the Plastigage before reinstalling the cap.
When using Plastigage, the readings can sometimes be
unclear. For example, all parts of the Plastigage are not
the same width Measure the major widths to make sure
that they are within the specification range. Also,
experience has shown that when checking clearances
tighter than 0.10 mm (.004") the readings may be low by
0.013 to 0.025 mm (.0005 to .0010"). Out-of-round
journals can give faulty readings. Also, journal taper may
be indicated when one end of the Plastigage is wider
than the other.
For complete details concerning measuring bearing
clearances, see Engine Bearings And Crankshafts, Form
Check the main bearing clearance with Plastigage
(B) as follows:
Put a piece of Plastigage (B) on the crankshaft
journals as shown
Make sure the part number on the main bearing cap
is toward the front of the engine and the number on
the main bearing cap is the same as the number on
the cylinder block on the left side of each main
Put main bearing caps (1) in position in the engine.
Put clean engine oil on the bolt threads and the face of
the washers, and install the bolts. Tighten the bolts to a
torque of 40 + 4 Nm (30 + 3 Ib.ft.).
Put a mark on each bolt and main bearing cap; then
tighten the bolts 90 more.
Remove the main bearing caps, and measure the
Plastigage to find the bearing clearance. The main
bearing clearance for new bearings must be 0.076 to 0
165 mm (.0030 to .0065 in.). Maximum permissible
clearance with used bearings is 0.25 mm (.010 in.).