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.

Replace both upper and lower halves if any defective condition is found. 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 crankcase bolt No.1 for deformation.

1) Remove lower crankcase.
2) Clean bearings and crankshaft journals.
3) Place plastic gauge (1) with the same width as the bearing, parallel to the crankshaft, avoiding oil hole.





4) Without applying sealant install lower crankcase. Removal and Installation
5) After three minutes, remove lower crankcase and use scale (2) on plastic gauge envelope (1) to measure plastic gauge width at the widest point.

NOTE:
If either of the following conditions exists for the crankshaft journal and the cylinder block journal together, different standard values are applied.
- 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 (0.0010 - 0.0014 in.)

For more information about stamped number and stamped alphabet.

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 Bearing
and recheck main bearing clearance.

If measured clearance with new bearings is out of standard, select other bearing using the following procedures and recheck main bearing clearance:

- More than standard:
Replace bearing with one size thicker or regrind crankshaft journal to undersize and use 0.25 mm undersize bearing (0.0098 in).
- Less than standard:
Replace bearing with one size thinner or regrind crankshaft journal to undersize and use 0.25 mm undersize bearing (0.0098 in).

Selection of Main Bearing

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 using 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 using the following procedures:
- There are five stamped alphabets (6) (any of "A" through "F") on Lower crankcase 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, each bearing is painted in the following colors at the position as shown in figure.

Each color represents 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 (0.0098 in.))

- 0.25 mm (0.0098 in.) undersize bearing is available, in five kinds varying in thickness.
To distinguish them, each bearing is painted in the following colors at the position as shown 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 (2.0367 - 2.0374 in.)

b Use micrometer to measure reground journal diameter. Crankshaft Inspection
c Use measured journal diameter above and alphabets on cylinder block to 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.

Crankcase Bolt No.1 Inspection

Measure each thread diameter at specified points on crankcase bolt No.1 (1) using micrometer (2).

Calculate difference in diameters ("A" - "B").

Replace with new one if it exceeds limit.

Crankcase bolt diameter measurement points
"a": 61.0 mm (2.40 in.)
"b": 98.0 mm (3.85 in.)

Crankcase cap bolt diameter difference
Limit ("A" - "B"): 0.13 mm (0.0051 in.)