When the OD of the front or rear main bearing journals are undersized, the standard solution is to have the bearing journals hard chromed and ground to size. An alternative solution is to use bearings with a smaller ID of the bearing inner race. In that case, the main bearing journal only needs to be groud to size. Following oversized ID’s are available: 0.01 – 0,02 – 0.03 – 0.04 – 0.05 – 0.06 – 0.07 – 0.08 – 0.09 – 0.10 – 0.11 – 0.11 – 0.12 – 0.14 mm Since these bearing have a standard CN axial clearance, the interference fit with the rear crankshaft bearing journal must be kept at the lower end of the crankshaft OD tolerance of +0.003 + 0.013 mm (so close to +0.003 mm) These bearings are no stock item. Delivery time on request. Shaeffler specifies an axial clearance of 120 – 220 micron for the 6207-M-CN bearing. (CN = standard radial tolerance: 6 – 20 micron) Firstly, the axial clearance will be largely eliminated by the interference fit of the bearing inner race on the crankshaft bearing journal, provided that the diameter of the bearing journal is within specification. The remaining axial clearance is the result of the tolerances of: a) the bearing inner race (35.000 -0.010 +0.000 mm) b) the bearing radial clearance (+0.006 +0.020 mm) c) the crankshaft bearing journal OD (35.000 +0.002 +0.018 mm front and 35.000 +0.003 + 0.013 mm rear) In the worst case tolerance scenario (resulting in maximum axial clearance), when the crankcase is at operating temperature the remaining clearance will be further reduced because of the difference in expansion between the crankshaft and the crankcase. However, when the engine is still cold, the crankshaft will be able to move axially by a distance equal to the remaining axial play of the bearings. For the rear crankshaft bearing, an interference fit of 0.03 to 0.05 mm is specified for the fit of the bearing in the crankcase bearing bushing. In the worst case tolerance scenario (resulting in 0 or a negative axial clearance) the ball bearing will seize. For this reason we recommend a C3 bearing for the rear crankshaft web. If the bearing journal OD and bearing bushing ID are out of specification, a CN bearing is recommended. Front crankshaft bearing for all 2-cylinders. Rear crankshaft bearing for R26, R27, R51/2 – R67/2, R50, R50/2, R60, R60/2 (R68, R50S, R69 and R69S use 20207 C3 rear crankshaft bearing: PN 07119983301) Tolerance class: CN (=radial internal clearance min. 6 µm max. 20 µm) Interference fit of inner bearing race with crankshaft bearing journal: 0.015 mm (BMW spec.) D = 72 mm d = 35 mm B = 17 mm
Ball bearing FAG 6207 M for crankshaft – brass cage – smaller ID from 0.01 to 0.014 mm ►see details!!
Pre-war, R26, R27, R51/2, R51/3, R67, R67/2, R67/3, R68, R50, R50/2, R50S, R60, R60/2, R69, R69S
(+30) 21 0522 6607
Κωδικός προϊόντος: 07119981245.O