John has hit the nail on the head – 90* is the magic number. Maybe I confused people (wouldn’t be the first time) by trying to explain where that 90* should be measured.
And no, Berger – thick you’re definitely not.
As mentioned ages ago, I often find it difficult deciding where to pitch an explanation, given the wide variety of knowledge / ability between members on this forum.
At the risk of further confusion, here’s the fuller explanation of my thoughts, which I was trying to avoid earlier…….
In order to hide from his wife the fact his girlfriend was in the office, a director might designate her as part of the ‘design team’. At least that’s what we assumed when we used to describe a particularly poor design as ‘designed by the director’s girlfriend’. I’m afraid BSA’s clutch falls into that category.
For a start, you have a hard ball, bearing on the hardened end of a shaft, with the shaft’s other (hardened) end bearing on a hard stud in the pressure plate. All with scotch mist for lubrication. Bad engineering and no wonder it’s not unusual to find the ball is worn flat or there’s a deep hollow in the ‘actuating cap’ centre. The rest of the mechanism is sadly not much better.
First, the clutch arm / cable angle. I set my levers (I have four bikes with these boxes) to be just under that angle with clutch engaged and just over when disengaged. Having 90* at mid point gives the longest period of best leverage with maximum travel of the clutch push rod. I believe this is the point John was making.
Secondly, that little clutch pushrod lever on the end of the clutch arm spindle. Again, for maximum travel of the push rod and to minimise the amount the ball wipes across its face, 90* is again the magic angle. As explained in previous posts, this is not achieved when the pushrod lever is at 90* with the pushrod, but rather when that angle exists between the pushrod and a line drawn between where the ball touches the rod and the centre of the clutch arm spindle. Because of the poor design, this may mean the ball is not in the centre of the pushrod, but we’re working with what we’ve got and so the ‘cleanest dirty shirt’ principle applies. Is it better to have the ball in the centre (though it won’t stay there as it wipes across the rod end face during use) but pushing sideways on the pushrod because the angle is nowhere near 90*, or is it better to have 90* but the ball not central on the rod? I prefer the latter, as the force is pushing directly along the line of the rod with virtually nil sideways thrust.
Finally, again as referred to in previous posts, the best way of minimising this grief is to keep the ball as close to the pushrod lever as possible. This can only be achieved by having the pushrod as long as possible (I cut ¼” silver steel to length and harden the ends) but there is a downside – as the clutch wears there’s little if any adjustment available (letting the clutch arm out a little to compensate defeats the purpose). Had the adjustment been at the clutch pressure plate instead, most of this grief would have been avoided. Did directors have girlfriends in their offices in the 30’s when these designs were dreamt up?
