Main Bearing Inspection
Main Bearing Inspection
Main Bearing, Crankshaft and Cylinder Block Removal and Installation
Visual Inspection
Check bearings for pitting, scratches, wear or damage.
If any defective condition is found, replace both upper and lower halves. Never replace either half without replacing the other half.
Main Bearing Clearance
NOTE:
- Do not rotate crankshaft while gauging plastic is installed.
- After checking main bearing clearance, check crank case bolt No.1 for deformation.
1) Remove lower crank case.
2) Clean bearings and crankshaft journals.
3) Place a piece of gauging plastic (1) over the full width of bearing (parallel to crankshaft) on journal, avoiding oil hole.
4) Install lower crank case. Removal and Installation
5) After three minutes, remove lower crank case and using scale (2) on gauging plastic envelop (1), measure gauging plastic width at its widest point.
NOTE:
If pair of crankshaft journal and cylinder block journal is in the following condition, different values are applied as standard.
- Stamped number for crankshaft journal diameter is "4", and stamped alphabet for cylinder block journal inside diameter is "A".
Standard: 0.019 - 0.031 mm (0.00075 - 0.00122 in.)
- Stamped number for crankshaft journal diameter is "9", and stamped alphabet for cylinder block journal inside diameter is "F".
Standard: 0.025 - 0.037 mm (0.00098 - 0.00145 in.)
For more information about stamped number and stamped alphabet, refer to Selection of Main Bearings.
Main bearing clearance
Standard: 0.022 - 0.034 mm (0.00087 - 0.00133 in.)
Limit: 0.050 mm (0.00196 in.)
If measured clearance is less than standard or more than service limit, replace main bearings with new ones referring to Selection of Main Bearings
and recheck main bearing clearance.
If measured clearance with new bearings is out of standard, select other bearings according to the following procedures and recheck main bearing clearance.
- More than standard:
Replace bearing with one size thicker or regrind crank shaft journal to undersize and use 0.25 mm undersize bearing (0.0098 in).
- Less than standard:
Replace bearing with one size thinner or regrind crank shaft journal to undersize and use 0.25 mm undersize bearing (0.0098 in).
Selection of Main Bearings
Standard size bearing
If engine is under one of the following conditions, select a new standard bearings as follows, and install it.
- Bearing is in defective condition.
- Bearing clearance is out of specification.
- Crankshaft or cylinder block is replaced.
1) Check crankshaft journal diameter according to the following procedures.
- There are five stamped numbers (any of "4" through "9") on crank web No.4 as shown in figure.
- Those numbers represent crankshaft journal diameter as follows.
- Determine crankshaft journal diameter for journals No.1 through No.5 using stamped numbers and following table.
Crankshaft journal diameter
2) Check cylinder block journal inside diameter according to the following procedures.
- There are five stamped alphabets (any of "A" through "F") on lower crank case as shown in figure.
- Those alphabets represent cylinder block journal inside diameter as follows.
- Determine cylinder block journal inside diameter for journals No.1 through No.5 using stamped alphabets and following table.
3) There are 5 kinds of standard bearings differing in thickness. To distinguish them, they are painted in the following colors at the position as shown in figure.
Each color indicated the following thickness at the center of bearing.
Standard size crankshaft main bearing thickness
4) Select new standard crankshaft bearings using stamped numbers for crankshaft journal diameter, stamped alphabets for cylinder block journal inside diameter and following table.
Main bearing cross - reference selection table (standard size)
Undersize bearing (0.25 mm)
- 0.25 mm undersize bearing is available, in five kinds varying in thickness.
To distinguish them, each bearing is painted in the following colors at such position as indicated in figure.
Each color represents the following thickness at the center of bearing.
Undersize of crankshaft main bearing thickness
- If necessary, regrind crankshaft journal and select undersize bearing to use with it as follows.
a Regrind crankshaft journal to the following finished diameter.
Finished crankshaft journal diameter
51.732 - 51.750 mm (2.03670 - 2.03740 in.)
b Using micrometer, measure reground journal diameter. Crankshaft Inspection
c Using measured journal diameter above and alphabets stamped on cylinder block, select an undersize bearing by referring to the following table.
Main bearing cross - reference table (under size)
d Install selected main bearings and measure bearing clearance.
If measured clearance is more than standard, replace bearings with one size thicker and recheck bearing clearance.
If measured clearance is less than standard, replace bearings with one size thinner and recheck bearing clearance.
Crank Case Bolt No.1 Inspection
Measure each thread diameter at specified points on crank case bolt No.1 (1) using micrometer (2).
Calculate difference in diameters ("A" - "B").
If it exceeds limit, replace with new one.
Crank case bolt diameter measurement points
"a": 61.0 mm (2.40 in.)
"b": 98.0 mm (3.86 in.)
Crank case cap bolt diameter difference
Limit ("A" - "B"): 0.013 mm (0.0051 in.)
