Main Bearings Inspection
Main Bearings InspectionMain Bearing General Information
NOTE:
Before inspecting main bearings, note the following points.
^ Service main bearings are available in standard size and 0.25 mm (0.0098 in.) undersize, and each of them has 5 kinds of bearings differing in tolerance.
^ Upper half of bearing (1) has oil groove (2) as shown in figure. Install this half with oil groove toward cylinder block.
^ Lower half of bearing does not have oil groove.
Visual Inspection
Check bearings for pitting, scratches, wear or damage.
If any malcondition 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.
Check clearance by using gauging plastic (1) according to the following procedure.
1. Remove lower crankcase.
2. Clean bearings and main journals.
3. Place a piece of gauging plastic (1) to full width of bearing (parallel to crankshaft) on journal, avoiding oil hole.
4. Install lower crankcase to cylinder block without applying sealant.
5. Remove lower crankcase, and using scale (2) on gauging plastic (1) envelop, measure gauging plastic (1) width at its widest point. If clearance exceeds its limit, replace bearing.
Always replace both upper and lower inserts as a unit.
A new standard bearing may produce proper clearance. If not, it will be necessary to regrind crankshaft journal for use of 0.25 mm undersize bearing.
After selecting new bearing, recheck clearance.
Main bearing clearance for standard size bearing
Standard: 0.0210 - 0.0390 mm (0.0009 - 0.0015 in.)
Limit: 0.0520 mm (0.0020 in.)
Main bearing clearance for undersize bearing
Standard: 0.0240 - 0.0420 mm (0.0010 - 0.0016 in.)
Limit: 0.0550 mm (0.0021 in.)
Selection of Main Bearings
Standard bearing
NOTE:
The meaning of "Upper" and "Lower" described in this procedure are the following.
^ Upper: It is meaning of main bearing installed in cylinder block side journal.
^ Lower: It is meaning of main bearing installed in lower crankcase side journal.
If engine is under one of the following conditions, select a new standard bearing as follow, and install it.
^ Bearing is in malcondition.
^ Bearing clearance is out of specification.
^ Crankshaft or cylinder block is replaced.
1. First check journal diameter. As shown in figure, crank web has stamped numbers and alphabet at the center.
Six kinds of numbers ("4" through "9") represent the following journal diameters.
Journal diameter
2. Next, check journal bore diameter.
On lower crankcase, 4 alphabets (1) are stamped as shown in figure.
Three kinds of alphabets (A, B and C) represent the following journal bore diameters.
Journal bore diameter
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 indicated in figure.
Each color indicates the following thickness at the center of bearing.
NOTE:
The following bearing are not supplied because they are unnecessary in this selection procedure.
^ Upper main bearing: Brown
^ Lower main bearing: Black
Standard size main bearing thickness
4. From number stamped on crank webs at its center and alphabets stamped on cylinder block lower side, determine new standard bearing to be installed to journal referring to cross reference table below.
For example, if number stamped on crank web is "4" and alphabet stamped on cylinder block is "A", install new standard bearing painted in "Black" to cylinder block side journal and "Colorless" to lower crankcase side journal.
Main bearing cross-reference table (standard bearing)
5. Using gauging plastic, check bearing clearance with newly selected standard bearing.
If clearance still exceeds its limit, use next thicker bearing and recheck clearance.
Undersize bearing (0.25 mm)
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 such position as indicated in figure.
Each color represents the following thickness at the center of bearing.
Undersize main bearing thickness
^ If necessary, regrind crankshaft journal and select undersize bearing to use with it as follows.
a. Regrind journal to the following finished diameter.
Finished journal diameter
64.7380 - 64.7560 mm (2.54874 - 2.54944 in.)
b. Using micrometer, measure reground journal diameter.
Measurement should be taken in two directions perpendicular to each other in order to check for out-of-round.
c. Using journal diameter measured and alphabets stamped on cylinder block, select undersize bearing referring to cross-reference table below.
Check bearing clearance with newly selected undersize bearing.
Main bearing cross-reference table (undersize bearing)
