Separation
1. To access the crankshaft and connecting rods, bearings, oil pump and transmission components, the crankcase must be split into two parts.
2. To enable the crankcases to be separated, the engine must be removed from the frame (see Section 5) and the following assemblies removed:
- Camshafts (Section 9)
- Cam chain tensioners (Section 11)
- Cylinder heads (Section 12)
- Cylinder barrels (Section 15)
- Water pump (Chapter 3)
- Starter motor (Chapter 9)
- Ignition pulse generator coils (Chapter 5)
- Clutch (Section 18)
- Gearchange mechanism (Section 20)
- Primary drive gear (Section 21)
- Alternator (Chapter 9)
- Starter clutch (Section 22)
- Cam chains (Section 10)
3. If required, unscrew the bolt(s) securing the oil seal retainer plate to the left-hand side of the crankcase and remove the plate, noting how it fits (see illustration).
23.3. Remove the oil seal retainer plate
4. Lay the engine on its right-hand side. Unscrew the 6 mm bolts in the left-hand side of the crankcase, followed by the 8 mm bolts (see illustration). Slacken the bolts evenly and a little at a time in a criss-cross pattern until they are all loose, then remove the bolts.
Note: each bolt is removed, store it in its relative position in a cardboard template of the crankcase halves. This will ensure all bolts are installed in the correct location on reassembly.
23.4. Crankcase 6 mm bolts (A) and 8 mm bolts (B)
5. Carefully turn the engine over onto its lefthand side and support it on wooden blocks so the end of the transmission output shaft is off the work surface. Unscrew the 6 mm bolts in the right-hand side of the crankcase, followed by the 8 mm bolts (see illustration 23.4). Slacken the bolts evenly and a little at a time in a criss-cross pattern until they are all loose, then remove the bolts. Note the copper sealing washer on the top 8 mm bolt in between the cylinders (see illustration).
23.5. Note the sealing washer (arrowed) with this bolt
Note: As each bolt is removed, store it in its relative position in a cardboard template of the crankcase halves. This will ensure all bolts are installed in the correct location on reassembly.
6. If the gear selector drum cam plate has not been removed (see Section 20). rotate it so that its outline shape matches the hole in the right-hand crankcase half, otherwise it will snag on the case when it is lifted (see illustration) Carefully lift the right-hand crankcase half off the left-hand half, using a screwdriver in the leverage points and a soft hammer to tap around the joint and gently on the shaft ends to initially separate the halves if necessary (see illustration)
23.6a. Rotate the selector drum cam plate until the arms match the holes in the crankcase
23.6b. Lift the right-hand crankcase half off the left-hand half
Note: If the halves do not separate easily, make sure all fasteners have been removed. Do not try and separate the halves by levering against the crankcase mating surfaces as they are easily scored and will leak oil. Use only the special leverage point. The right-hand side crankcase half will come away by itself, leaving the oil pump, crankshaft, transmission shafts, selector drum and selector forks in the lefthand crankcase half.
7. Remove the two locating dowels from the crankcase if they are loose (they could be in either crankcase half), noting their locations (see illustration). If the oil pump and its pipe are not being disturbed, remove the exposed O-ring from the oil pipe, noting which way up it fits, and discard it as a new one must be used. Check that the thrust washer is on the right-hand end of the transmission outpu! shaft: if not, it is probably stuck to the bearing in the right-hand crankcase half.
23.7. Remove the dowels (A) if loose, renew the O-ring (B), and note the thrust washer (C)
Reassembly
8. Remove all traces of sealant from the crankcase mating surfaces. Support the left-hand half on wooden blocks so the end of the transmission output shaft is off the work surface.
9. Ensure that all components and their bearings are in place in the right and left-hand crankcase halves. If the oil pump and Its pipe have not been removed, install a new O-ring, with its tapered side facing out, onto the exposed end of the pipe (see illustration 23.7). Check that the thrust washer is installed on the right-hand end of the transmission output shaft.
10. Generously lubricate the transmission shafts, selector drum and forks, and the crankshaft, particularly around the bearings, with molybdenum disulphide oil (a mixture of 50% molybdenum disulphide grease and 50% engine oil), then use a rag soaked in high flash-point solvent to wipe over the gasket surfaces of both halves to remove all traces of oil.
11. Install the two locating dowels in the lefthand crankcase half (see illustration 23.7).
12. If installed, make sure the selector drum cam plate is positioned as on removal to allow the right-hand crankcase half to fit over it (see illustration 23.6a). Also make sure that each connecting rod is positioned correctly for its cylinder.
13. Apply a small amount of suitable sealant to the mating surface of the right-hand crankcase half (see illustration).
23.13. Apply a sealant to the mating surface of the right crankcase half
Caution: Do not apply an excessive amount of sealant, as it will ooze out when the case halves are assembled and may obstruct oil passages.
14. Check again that all components are In position, then carefully fit the right-hand crankcase half onto the left-hand half (see illustration 23.6b). Make sure the dowels, oil pipe and shaft ends all locate correctly into the right-hand crankcase half. Note that it is easy for the oil pipe rim to contact the rim of its socket in the right-hand half and so prevent the crankcase seating. Insert a screwdriver into the gap between the crankcase halves and move the pipe slightly while applying light downward pressure on the crankcase - as soon as the pipe aligns with its socket the crankcase will lower onto it.
15. Check that the right-hand crankcase half is correctly seated. Note: The crankcase halves should fit together without being forced. If the casings are not correctly seated, remove the right-hand half and investigate the problem. Do not attempt to pull them together using the bolts as the casing will crack and be ruined.
16. Clean the threads of the right-hand crankcase bolts and insert them in their original locations (see illustration 23.4). Make sure the copper sealing washer is installed with the top 8 mm bolt in between the cylinders (see illustration 23.5). Secure all bolts hand-tight at first, then tighten the 8 mm bolts followed by the 6 mm bolts evenly and a little at a time in a criss-cross pattern to the torque settings specified at the beginning of the Chapter. When torquing the bolts, be sure to distinguish correctly between the 8 mm bolts and the 6 mm bolts.
17. Clean the threads of the left-hand crankcase bolts and install them in their original locations (see illustration 23.4). Secure all bolts hand-tight at first, then tighten the 8 mm bolts followed by the 6 mm bolts evenly and a little at a time in a criss-cross pattern to the torque settings specified at the beginning of the Chapter. When torquing the bolts, be sure to distinguish correctly between the 8 mm bolts and the 6 mm bolts.
18. With all crankcase bolts tightened, check that the crankshaft and transmission shafts rotate smoothly and easily. Select each gear in turn and check the operation of the transmission in each gear, then select neutral and check that the shafts can turn freely and Independently of each other. If there are any signs of undue stiffness, tight or rough spots, or of any other problem, the fault must be rectified before proceeding further.
19. Install all other removed assemblies in the reverse of the sequence given in Steps 2 and 3. Apply a suitable non-permanent threadlocking compound to the oil seal retainer plate bolts (see illustration 23.3).