12. Dismantling the engine unit: removing the crankshaft
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.
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.
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
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.
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.