Barry,
If you look into the timing chest, you will see that the valve gear is clamped to the crankcases by the 4 main studs through the cases. It is imperitive that these studs are tightened in the correct sequence. Starting from the LH side, tighten the 4 nuts (2 are behind the primary chaincase, and 2 actually secure the chaincase). With these nuts tightened, you will see that the crankcases and the mounting blocks for the cam followers are now firmly clamped together. The outrigger plate that supports the cam spindles (and carries the timed breather) can now be fitted, along with the timed breather (this is also a good time to loosely fit the banjo bolt for the oil feed). With everything correctly aligned, the 3 nuts, the banjo bolt and the 2 cam spindle nuts can be fully tightened. At this point, all the valve gear should be firmly located within the timing chest (even gentle leverage with a screwdriver shouldn't cause the outrigger plate to move!). Prolonged running with the outrigger plate free to move has been known to result in loose cam spindles, and in extreme cases, a broken off oil feed post (for the outrigger plate). When you are satisfied everything is OK, refit the timing cover, but don't overtighten the securing nuts. Overtightening usually results in cracks across the bottom 2 holes.
Hope this is of some help,
Regards,
Eddie.