Main Bearings, Crankshaft and Cylinder Block Inspection
Main Bearings, Crankshaft and Cylinder Block InspectionCrankshaft
Crankshaft runout
Using a dial gauge, measure runout at center journal. Rotate crankshaft slowly. If runout exceeds its limit, replace crankshaft.
Limit on runout 0.06 mm (0.0023 in.)
Crankshaft thrust play
Measure this play with crankshaft set in cylinder block in the normal manner, that is, with thrust bearing and lower crankcase installed. Tighten crankcase bolts.
Use a dial gauge to read displacement in axial (thrust) direction of crankshaft. If its limit is exceeded, replace thrust bearing with new standard one or oversize one to obtain standard thrust play.
Crankshaft Thrust Play
Standard: 0.10 - 0.35 mm (0.0039 - 0.0137 in.)
Limit: 0.42 mm (0.0149 in.)
Thickness of crankshaft thrust bearing
Out-of-round and taper (uneven wear) of journals
An unevenly worn crankshaft journal shows up as a difference in diameter at a cross section or along its length (or both). This difference, if any, is determined by taking micrometer readings. If any one of journals is badly damaged or if amount of uneven wear in the sense exceeds its limit, regrind or replace crankshaft.
Limit on out-of-round and taper
0.01 mm (0.0004 in.)
Out-of-round
"A"-"B"
Taper
"a"-"b"
Main Bearings
Main bearings general information
^ Service main bearings are available in standard size and 0.25 mm (0.0098 in.) undersize, and standard size 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 to cylinder block.
^ Lower half of bearing does not have oil groove.
Main bearings 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
Check clearance by using gauging plastic 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.
NOTE: Do not rotate crankshaft while gauging plastic is installed.
5. Remove lower crankcase and using scale (2) on gauging plastic envelop (1), measure gauging plastic 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
Standard: 0.020 - 0.038 mm (0.00079 - 0.00149 in.)
Limit: 0.063 mm (0.0024 in.)
Selection of main bearings
STANDARD BEARING:
If engine is under the following conditions, select a new standard bearing as followings 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 No.2 has stamped numbers. Six kinds of numbers ("4" through "9") represent the following journal diameters.
Journal diameter
Journal diameter:
Stamped numbers on crank web No.2 (3) represent journal diameters marked with an arrow in figure respectively. For example, stamped number "5" indicates that corresponding journal diameter is 58.0000 - 58.0029 mm (2.28346 - 2.28357 in.).
2. Next, check journal bore diameter. On lower crankcase five alphabets are stamped as shown in figure.
Three kinds of alphabets ("A", "B" and "C") represent the following journal bore diameters.
Journal bore diameter
Stamped alphabets on lower crankcase represent journal diameter marked with an arrow in figure respectively.
For example, stamped alphabet "A" at No.2 journal indicates that (journal) bore diameter of No.2 journal is 61.9940 62.0000 mm (2.44070 - 2.44094 in.).
3. There are 5 kinds of standard bearings differing in thickness. To distinguish them, they are painted (1) in the following colors at the position as indicated in figure. Each color indicates the following thickness at the center of bearing.
Standard size main bearing thickness
4. From number stamped on crank web No.2 and alphabets stamped on lower crankcase, determine new standard bearing to be installed to journal by referring to table shown. For example, if number stamped on crank web No.2 is "5" and alphabet stamped on lower crankcase is "A", install new standard bearings painted in "Green" to cylinder block side journal and "Black" to lower crankcase side journal.
NOTE: The meaning of "Upper" and "Lower" described in below table are the following.
^ Upper: It is instruction of main bearing installed in cylinder block side journal.
^ Lower: It is instruction of main bearing installed in lower crankcase side journal.
Main bearing cross-reference table (new standard bearing)
5. Check main 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 undersize bearing is available, in five kinds varying in thickness.
To distinguish them, each bearing is painted (1) 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 under-size bearing to use with it as follows.
a. Regrind journal to the following finished diameter.
Finished journal diameter 57.7380 - 57.7560 mm (2.27315 - 2.27385 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 lower crankcase, select an undersize bearing by referring to the following table.
Check bearing clearance with newly selected undersize bearing.
Undersize bearing specification
Crankshaft Position Sensor Plate
Check teeth of plate for damage.
If any damage is found, replace crankshaft (1).
Oil Pump Sprocket
Check teeth of sprocket for wear or damage.
If any damage or wear is found, replace crankshaft (1).
Oil Pump Chain
Check oil pump chain for wear or damage.
Flywheel
^ If ring gear is damaged, cracked or worn, replace flywheel.
^ If the surface contacting clutch disc is damaged, or excessively worn, replace flywheel.
^ Check flywheel for face runout with a dial gauge. If runout exceeds its limit, replace flywheel.
Limit on runout 0.2 mm (0.0078 in.)
Cylinder Block
^ Distortion of gasket surface.
^ Using straightedge and thickness gauge, check gasket surface for distortion and, if flatness exceeds its limit, correct It.
Flatness Limit 0.06 mm (0.0024 in.)
Honing or reboring cylinders
1. When any cylinder needs reboring, all other cylinders must also be rebored at the same time.
Oversize piston specification
2. Using micrometer, measure piston diameter.
3. Calculate cylinder bore diameter to be rebored as follows.
D = A + B - C
D: Cylinder bore diameter to be rebored.
A: Piston diameter as measured.
B: Piston clearance = 0.02 - 0.04 mm (0.0008 - 0.0015 in.)
C: Allowance for honing = 0.02 mm (0.0008 in.)
4. Rebore and hone cylinder to calculated dimension.
NOTE: Before reboring, install lower crankcase and tighten to specification to avoid distortion of bearing bores.
5. Measure piston clearance after honing.
Check Valve
Check check valve for clogging and ball for being stuck.
