Manual - Chapter 1 Engine

11. Dismantling the engine unit: removing the crankcase lower section and the output/balancer shaft

  1. While these components can be removed with the main cylinder block casting still in the frame, this is not recommended. It will leave the engine unit supported precariously at its rear end and attached the frame by two bolts (only one if the cylinder head is removed) and a few ancillary components; when one realizes that the frame is supported only by the front wheel and its rear end, the potential for serious damage and personal injury may be appreciated.
  2. Since the removal of the engine/transmission unit complete involves so little extra work and affords so much safer working conditions and improved access, it is the only recommended method of gaining access to these components.
  3. Owners who wish to carry out the work with the engine in the frame (against the above advice) should note that the gearbox and final drive must be removed (Chapter 3 - Gearbox and Chapter 8 - Final Drive) the clutch must withdrawn (Chapter 2 - Clutch) and the bellhousing removed (Section 7 - removing the bellhousing and auxiliary drive shaft components). All the engine oil must be drained and the filter removed (see Routine Maintenance - Change the engine oil) and the sump and oil pump pick-up removed (Chapter 5 - Fuel & Oil). Finally the coolant must be drained and the oil/water pump assembly must be removed (Chapter 4 - Cooling and Chapter 5 - Fuel & Oil).
  4. Remove the Allen screws along the left- and right-hand mounting surfaces of the crankcase lower section, then remove the two hexagon-headed bolts from the inside rear and the two Allen-headed bolts or screws from the inside front. Tap the lower section with a soft-faced mallet to break the joint and withdraw the lower section noting the 0-rings around the oil and coolant passages and the two to locating dowels, one next to each output shaft bearing. Unless the dowels are firmly fixed in the crankcase/cylinder block, they should be removed. 
  5. On 75 models, slowly rotate the crankshaft and balancer shaft until the timing marks can be seen. These should be in the form of a straight line on the crankshaft gear which aligns with either a dot or a V mark on the balancer gear. Do not disturb either shaft until the marks have been found and noted.
  6. Withdraw the output/balancer shaft and its rear seal noting that its front needle roller bearing is loosely fixed and may drop clear.
  7. On some early models whose output shafts are fitted with rear bearings which have a thin (1.75 mm/0.07 in thick) locating circlip at the forward end of the bearing outer race, the bearing may be glued in place with Loctite 273, Three Bond 1110 B or similar adhesive. If any difficulty is encountered in removing such a bearing, the adhesive should be heated (maximum of 300 °C/572 °F) to break it down and to release the bearing.


11.6a Remove crankcase lower section to release outputs shaft....


11.6b ....noting that front bearing is loose and may drop clear.