Piston, Piston Rings, Connecting Rods and Cylinders
INSPECTIONCylinders
^ Inspect cylinder walls for scratches, roughness, or ridges which indicate excessive wear. If cylinder bore is very rough or deeply scratched, or ridged, rebore cylinder and use oversize piston.
^ Using a cylinder gauge, measure cylinder bore in thrust and axial directions at two positions as shown in figure. If any of following conditions is noted, rebore cylinder.
1. Cylinder bore diameter exceeds limit.
2. Difference of measurements at two positions exceeds taper limit.
3. Difference between thrust and axial measurements exceeds out-of-round limit.
Cylinder Bore Diameter Limit: 75.15 mm (2.9586 inch)
Tapper And Out-of-Round Limit: 0.10 mm (0.0039 inch)
NOTE: If any one of four cylinders has to be rebored, rebore all four to the same next oversize. This is necessary for the sake of uniformity and balance.
Pistons
^ Inspect piston for faults, cracks or other damaged. Damaged or faulty piston should be replaced.
^ Piston diameter: As indicated in figure, piston diameter should be measured at a position 15 mm (0.59 inch) from piston skirt end in the direction perpendicular to piston pin.
Piston Diameter:
Standard: 74.970 - 94.990 mm (2.9516-2.9523 inch)
Oversize 0.25 mm (0.0098 inch): 75.220 - 75.230 mm (2.9614 - 2.9618 inch)
0.50 mm (0.0196 inch): 75.470-75.480 mm (2.9712 - 2.9716 inch)
^ Piston clearance: Measure cylinder bore diameter and piston diameter to find their difference which is piston clearance. Piston clearance should be within specification as given below. If it is out of specification, rebore cylinder and use oversize piston.
Piston Clearance: 0.02 - 0.04 mm (0.0008 - 0.0015 inch)
NOTE: Cylinder bore diameters used here are measured in thrust direction at two positions.
^ Ring groove clearance: Before checking, piston grooves must be clean, dry and free of carbon. Fit new piston ring into piston groove, and measure clearance between ring and ring land by using thickness gauge. If clearance is out of specification, replace piston.
Ring Groove Clearance:
Top: 0.03 - 0.07 mm (0.0012 - 0.0027 inch)
2nd: 0.02 - 0.06 mm (0.0008 - 0.0023 inch)
Piston Pin
^ Check piston pin, connecting rod small end bore and piston bore for wear or damage, paying particular attention to condition of small end bore bush. If pin, connecting rod small end bore or piston bore is badly worn or damaged, replace pin, connecting rod or piston.
^ Piston pin clearance: Check piston pin clearance in small end. Replace connecting rod if its small end is badly worn or damaged or if measured clearance exceeds limit.
Piston Clearance In Small End:
Standard: 0.003 - 0.016 mm (0.0001 - 0.0006 inch).
Limit: 0.05 mm (0.0020 inch).
Small-End Bore: 19.003 - 19.011 mm (0.7482 - 0.7486 inch).
Piston Pin Diameter: 18.995 - 19.000 mm (0.7479 - 0.7480 inch).
Piston Rings
To measure end gap, insert piston ring into cylinder bore and then measure the gap by using thickness gauge. If measured gap is out of specification, replace ring.
Piston Ring End Gap:
Top Ring:
Standard: 0.2 - 0.35 mm (0.0079-0.0137 inch)
Limit: 0.7 mm (0.0275 inch)
2nd Ring:
Standard: 0.2 - 0.35 mm (0.0079 - 0.0137 inch)
Limit: 0.7 mm (0.0275 inch)
Oil Ring;
Standard: 0.2 - 0.7 mm (0.0079 - 0.0275 inch)
Limit: 1.7 mm (0.0669 inch)
NOTE: Decarbon and clean top of cylinder bore before inserting piston ring.
Connecting Rod
^ Big-end side clearance: Check big-end of connecting rod for side clearance, with rod fitted and connected to its crank pin in the normal manner. If measured clearance is found to exceed its limit, replace connecting rod.
Big-End Side Clearance:
Standard: 0.10 - 0.20 mm (0.0039 - 0.0078 inch)
Limit: 0.35 mm (0.0137 inch)
^ Connecting rod alignment: Mount connecting rod on aligner to check it for bow and twist and, if limit is exceeded, replace it.
Limit On Bow: 0.05 mm (0.0020 inch)
Limit On Twist: 0.10 mm (0.0039 inch)
Crank Pin and Connecting Rod Bearings
^ Inspect crank-pin for uneven wear or damage. Measure crank pin for out-of-round or taper with a micrometer. If crank pin is damaged, or out-of-round or taper is out of limit, replace crankshaft or regrind crank pin to undersize and use undersize bearing.
Connecting Rod Bearing Size:
Standard Diameter: 43.982 - 44.000 mm (1.7316- 1.7322 inch)
0.25 mm (0.0098 inch) Diameter: 43.732 - 43.750 mm (1.7218- 1.7224 inch)
Out-of-Round And Taper Limit: 0.01 mm (0.0004 inch)
^ Rod bearing:
Inspect bearing shells for signs of fusion, pitting, burn or flaking and observe contact pattern. Bearing shells found in defective condition must be replaced. Two kinds of rod bearing are available; standard size bearing and 0.25 mm undersize bearing. To distinguish them, 0.25 mm undersize bearing has the stamped number (US025) on its backside as indicated in figure, but standard size one has no number.
Rod Bearing Clearance
1. Before checking bearing clearance, clean bearing and crank pin.
2. Install bearing in connecting rod and bearing cap.
3. Place a piece of gauging plastic the full width of crankpin as contacted by bearing (parallel to crankshaft), avoiding oil hole.
4. Install rod bearing cap to connecting rod. When installing cap, be sure to point arrow mark on cap to crankshaft pulley side, as shown in figure. After applying engine oil to rod bolts, tighten cap nuts to specified torque. DO NOT turn crankshaft with gaging plastic installed.
Tightening Torque (a): 35 Nm (3.5 kg-m, 25.5 ft. lbs.)
5. Remove cap and using a scale on gaging plastic envelope, measure gaging plastic width at the widest point (clearance). If clearance exceeds its limit, use a new standard size bearing and remeasure clearance.
Bearing Clearance:
Standard: 0.020 - 0.050 mm (0.0008 - 0.0019 inch).
Limit: 0.080 mm (0.0031 inch).
6. If clearance can not be brought to within its limit even by using a new standard size bearing, regrind crankpin to undersize and use 0.25 mm undersize bearing.