Andrew Birkett's nobugs.org
(andy@nobugs.org, June 2001)
I had to replace the lower yoke on the CG125 after I broke one of the pinch bolts off. I found a reasonably priced one from a breakers in MCN and had them mail it up to me. When it got here, I tried to put new pinch bolts into it. One went in fine, but the other wouldn’t start on the thread.
At first, I thought the thread had been chewed but that seemed strange since the yokes had came without pinch bolts, so the old bolts must have come out okay. I put that thought to the side while I tried cleaning the threads with WD40, which didn’t help. Real soon, I was at the point of trying to find an 8mm tap to redo the threads.
Fortunately, I didn’t own one and was forced to give up for the meantime and go to work. That evening, still without a tap to continue the job I was despondantly twiddling with the yoke and bolt I noticed that the top (unthreaded) part of the pinch bolt was pressing against the hole which it goes through.
penny drops
It wasn’t the thread. The reason the bolt wasn’t getting started was because the two sides of the pinch ring weren’t aligned. Whenever the bolt was aligned with the threads, the top half would get wedged against the side of its hole. So, all that was required was to get the two halves of the pinch ring to be aligned and, hey presto, the bolt goes in without a problem.
It’s interesting how I jumped to conclusions on this one. I assumed that because the bolt wasn’t getting started on the thread (the bolt was new, and it went in the other pinch ring fine) that the thread in the yoke was wrong. If I’d actually tried to use a tap to clean up the threads, I’d probably just damaged them. In the end, the only reason I noticed what was really wrong was because I had ran out of things to try (ie. I didn’t own an 8mm tap) and was just idly playing with the yoke and bolt. It would go in about half a turn and then stick. At one point, I put it in just about a quarter of a turn and wiggled it to feel what free play there was (bolts always have free play until they’re snug) and noticed that it was knocking against the side of the hole. After that, it was obvious that it was the misalignment which was stopping the bolt going in.
I’d encountered lots of stuck bolts and duff threads before, but not many misaligned holes. So, I guess I was just fitting the problem at hand to the closest thing I’d experienced before, without actually fully checking out the evidence before me.
It further convinces me that the most important thing to do when you start having problems is to stop and have a break for a few minutes, hours or days. Otherwise, you’ll latch onto the first idea which comes into your mind, and suffer any bad consequences from not taking the time to think about alternatives. It’s a “can’t see the wood for the trees” problem. I’ve found that I’m more susceptible to this when I’m in a hurry.