Manual - Chapter 1 Engine

23. Examination and renovation: crankshaft and main bearings

  1. The crankshaft should be cleaned. Be very careful to check that all oilways are completely free from dirt and other foreign matter.
  2. If required, the ignition rotor flange and cam chain drive sprocket can be withdrawn. Unscrew the rotor retaining bolt and pull the flange and sprocket off the shaft end; a puller may be required to withdraw the flange. Note that the sprocket will fit either way round and that the locating pin set in the rotor flange passes through the sprocket to locate the two components by engaging a crankshaft keyway.
  3. On reassembly, place the sprocket on the crankshaft end and refit the rotor, ensuring that both components are correctly located by the pin. Refit the retaining bolt and tighten it to the specified torque setting.
  4. Examine the crankshaft closely. Any obvious signs of damage such as marked bearing surfaces, damaged threads, worn tapers and damaged gear teeth will mean that it must be renewed. There are, however, light engineering firms advertising in the motorcycle press who can undertake major crankshaft repairs; in view of the expense of a new component it is worth trying such firms provided they are competent.
  5. Refit temporarily the crankshaft and use feeler gauges to measure the clearance between the crankcase bearing pedestals and their respective adjacent webs. Alternatively, a dial gauge can be mounted parallel to the crankshaft and with its tip touching one end. Push the crankshaft fully away from the gauge, zero the gauge, push the crankshaft fully towards the gauge again and note the reading obtained. If the crankshaft endfloat exceeds the specified limit the thrust bearings must be renewed. Crankshaft runout is measured using a dial gauge with the crankshaft mounted on V-blocks at each outer main bearing journal; runout measured at the centre main bearing journals, must not be excessive. If any doubt arises about the amount of runout measured, seek expert advice.
  6. The procedures for examining the bearing inserts and journals, measuring the diameters of the crankshaft journals, and measuring the amount of wear on existing bearing inserts are the same as for the big-end bearings. Refer to paragraphs 6-9 of Section 22 of this Chapter. It will of course be necessary to reassemble temporarily the main bearing caps, tightening all securing bolts to the correct torque setting, when using Plastigage to check the bearing radial clearances.


23.2a If required, unscrew retaining bolt to release ignition rotor and sprocket from crankshaft front end ...


23.2b ... noting that puller may be required - note temporarily refitted to protect crankshaft end


23.3 Note that locating pin locates both sprocket and rotor with crankshaft keyway


23.5 Measuring crankshaft endfloat