Inspection: Main bearing span when free
•If the measurement is below the specified limit, replace both the upper and lower bearings as a set.
•Inspection: Main bearing-to-crankshaft oil clearance
– Fit the upper bearing into the upper crankcase and the lower bearing into the lower crankcase.
– Tighten the main cap bolts to a torque of 20 N·m {2.0 kgf· m}.
– Measure the inside diameter of the main bearing and the diameter of the corresponding crankshaft journal.
– If the difference between the measurements exceeds the specified limit, machine the crankshaft journal to one of the specified undersized dimensions.
Inspection: Crankshaft
[Inspection]
(1) Bend
• Support the crankshaft at its No. 1 journal and No. 5 journal.
Measure the extent of bending in the crankshaft at the center of the No. 3 journal. A half of the dial gauge reading obtained as the crankshaft is rotated by a full turn represents the bend of the crankshaft.
• If the measurement exceeds the specified limit, replace the crankshaft.
(2) Out-of-roundness and taper of crankshaft journals and pins
• If any of the measurements exceeds the specified limit, grind the crankshaft journal(s) and/or pin(s) to undersize(s) or replace the crankshaft.
Grinding of crankshaft
– Make sure of necessary undersize dimensions in the maintenance standard table and carry out grinding work in accordance with the following procedure.
– Do not change the center-to-center distance A between the journal and pin.
– Do not change the journal width B and the pin width C.
– Finish the fillets D smoothly.
– Carry out a magnetic inspection to check for cracks possibly caused by grinding. Also, check that the hardness of the surface has not dropped below Shore hardness number (Hs) 75.
– Replace the crankshaft if defects are evident.
• When grinding, turn both the crankshaft and the grinder counterclockwise as viewed from the crankshaft front end.
• When finishing the crankshaft with whetstone or sandpaper, rotate the crankshaft clockwise.
•Inspection: Distortion of upper crankcase top surface
– If the measurement exceeds the specified limit, grind the crankcase top surface with a surface grinder.
– Limit the amount of removed metal to make sure that the amount of piston projection above the crankcase top surface stays within the standard value range. (See the PISTON AND CONNECTING ROD section.)
