Manual - Chapter 1 Engine

12. Dismantling the engine unit: removing the crankshaft

  1. As mentioned in Section 3 - Dismantling the engine unit: general, the crankshaft can be removed whether or not the engine unit is in the frame. It is possible, if required, to remove the crankshaft by draining the coolant and removing the engine outer covers (Section 6), removing the cam chain from the crankshaft and camshafts (Section 8), and releasing the big-end caps from the crankshaft (Section 10). If their removal is not necessary, and provided that care is taken not to allow them to touch the valves, the pistons can be left in the bores while the crankshaft is removed and refitted. This avoids the need to remove the cylinder head.
  2. Owners of 75 models should check whether the crankshaft/balancer shaft marks are visible as soon as the crankshaft cover is removed. lf these timing marks cannot be seen, the crankcase lower section and balancer shaft must be removed to permit the marks to be aligned on reassembly. See Section 11. If the cylinder head is to be removed, removing the entire engine/transmission unit involves so little extra work and produces so much better access and safer working conditions that it is strongly recommended.
  3. With the preliminary dismantling operations that are described above carried out, inspect the main bearing caps, making careful written notes of how each cap can be identified and how its original fitted position can be indicated. Look for paint spots, manufacturer's stamped marks and any other identifying features; note all these and if necessary make your own.
  4. The component parts of the machine featured in the accompanying photographs were marked as follows, counting the main bearings consecutively from front to rear, number 1 being next to the cam chain; to bearing caps number 1, 2 and 3 were stamped with the figure 1, 2 or 3 respectively on the 'lower' exhaust retaining bolt boss, also at the base of the cap 'lower' end. Number 4 bearing cap carried the thrust bearing and number 5 carried no identification at all; to be safe a hammer and a small punch were used to mark the sides of the 'lower' retaining bolt boss of each cap, making one mark for bearing number 1, two for 2 and so on. Check for similar marks on the machine being overhauled and note that on 75 models bearing caps numbers 1 and 2 are numbered, number 3 carries the thrust bearing and number 4 is unmarked. When the caps are removed, note that the bearing shell locating tang grooves/oilways of each cap and the crankcase are aligned against each other on the 'lower' side of each bearing.
  5. Working evenly, by one turn at a time, unscrew the two bolts securing each main bearing cap, tap the cap firmly but gently with a soft-faced mallet to release it and withdraw it, noting which way round it is fitted. To ensure an even release of pressure first slacken all the bolts and then remove the caps in the following sequence: 75 models, rear bearing, front bearing (number 1 ), number 3, number 2 - 100 models, rear bearing (number 5), front bearing (number 1), number 4, number 2, number 3.
  6. With all caps removed, lift out the crankshaft.

12.3 Before removing crankshaft main bearings caps....

12.4a ....make notes of any marks identifying each cap's fitted position (arrows) ....

12.4b ....and if necessary make your own - see text