5_108.bk Page 145 Thursday, October 4, 2001 11:45 AM
REPAIR INSTRUCTIONS CRANKSHAFT INSPECTION Description The crankshaft is fully counterbalanced and journals are induction-hardened. There are seven main bearings. Thrust washers located at the center main bearing (position No. 4) absorb fore and aft end thrust. Crankshaft extension at forward end carries the main drive gear, vibration damper and accessory drive pulleys. The main drive gear has a shrink fit and the vibration damper hub has a press fit. The main drive gear is keyed to the crankshaft and proper assembly is important for engine timing. The flywheel is mounted to a flange at rear of crankshaft. Two seals, one at the front and one at the rear, prevent engine lubricating oil from leaking around ends of the crankshaft. Bearing caps are furnished with the crankcase and support the crankshaft in true alignment. Webs integral to the crankcase provide upper half of main bearing supports. Removable caps provide lower support. Capscrews hold the caps in position. The bearing caps are not interchangeable and each has a number stamped on it which signifies its correct location and alignment in the crankcase. The caps are numbered 1 through 7, with No. 1 main bearing cap in front of engine. The bearing inserts are precision-designed. Bearings are inserted between the crankshaft and crankcase, and between the crankshaft and bearing caps. Thrust flanges to support thrust washers are located at the center main bearing (No. 4).
Extreme care must be taken to guarantee cleanliness of crankcase, crankshaft, and bearings during servicing and after service has been completed. Whenever possible, crankshaft should be removed when bearings are being installed in order to clean crankcase thoroughly. All bearing surfaces must be free of grit and burrs. Small particles of dust and dirt left between crankshaft and bearings will cause rapid wear and scoring of crankshaft journal and inserts. Any foreign material left between bearings and crankshaft bearing caps will cause distortion of bearing and a reduction in operating clearance at that point. The resulting frictional heat will cause bearing material to melt away from steel backing of bearing at that point. Such melted material will create further hot spots until complete bearing failure occurs. Anything that interferes with operating clearance of any bearing, or proper heat dissipation, affects bearing life. Cleanliness cannot be overstressed.
Inspection
If crankshaft journals are worn, out of round, or tapered, order a new crankshaft or exchange kit through the MACK parts system. New and exchange crankshafts are available through MACK distribution centers. 1. Inspect crankshaft journals for straightness, out-of-round, taper, and surface finish. 2. Visually check crankshaft for any apparent cracks, worn journals and damage to threads, dowel or main drive gear. 3. Magnaflux the crankshaft. This process requires special equipment and application methods. 4. Using standard machinist inspection practice, check crankshaft for straightness. 5. Measure crankshaft journals with a micrometer. Measure each journal in two locations, 90 degrees apart, and record measurements. 6. Check measurements against specifications in “FITS AND LIMITS” on page 289. Page 145
