Talking about 'trial and error', I've had what you may call a 'learning experience' this week which I think may be useful in the context of this thread. The worry has been expressed by a few people that the threads will shear due to over-tightening.
Fear Not!!! The bolt will break before the threads fail. I know.
On Sunday eve, during a chain tightening, one of the heads on the M8 grub screws sheared off. The screw body was lodged tight into the stainless braze-on. I was stumped! The bike is a few years old, and I think some over-zealous tightening (probably mine!) did for the screw. Try as I might, I couldn't shift it - I have a decent cobalt steel 4mm drill bit, and I also have a set of easy out left-handed taps, but it wouldn't shift.
Then, this morning, after a couple of days 'cooling off' while away with work, I rang round and found a great small precision engineering company. The boss was a lovely guy, but his shop was buried with work (which is a good thing I guess). But his next-door neighbour, another precision engineer, was happy to take the frame in there and then. I went home feeling like one of my nearest and dearest was going under the knife. He had promised to try and tap out a new thread, and so there was still the problem of getting a new grub screw to fit (the close threading on the Thorn screw is unusual, I understand).
Anyway, 3pm, the guy rang and told me the bike was ready. They had got a decent vertical drill on it, and (goodness knows how, because the frame must be a nightmare to hold) once they had drilled most of the bolt, it started spinning, no easy-out needed. And best of all......the thread was intact!!!
So, here are some pics of what goes on inside the EBB shell that might help answer the questions being posed on this thread.
above is the frame with the EBB shell now loosened and removed.
above is the really interesting one - showing the screw heads protruding into the BBshell. Now these screws are at this point finger-tight - and this is how much they will be inside the shell already - there really isn't much effort needed to get a positive hold!
above - the same setup, but from outside the shell. See how much thread is still showing on the screws!
So, a happy ending thank goodness. I have taken the opportunity to fit a new EBB shell, so the contact points should be spot on; the bb itself is perfect, and one ride so far has revealed silence in the bb area, so a proper ride some time tomorrow is planned to test my work. Incidentally, apart from the damage caused from drilling the screw out, the old EBB shell was not significantly damaged by over-tightening; it is really a tough piece of metal.
