Not so much a missing link, as a fat link
I retired from work last year and got a new touring bike, a Thorn Raven, with which I am very pleased. At the same time, I got a carbon fibre Ridley Orion racing bike. My daughter Lizzie, who's the family tyrant and a triathlete, insisted on this so she had to be obeyed. This was equipped with a compact chainset (52/14) rather than a triple, which I would've liked, as it wasn't available in this model, the Ridley Orion.
From the word go, I had drivetrain problems. The chain skipped unpredictably. I could not fix it. I'm a very experienced bike mechanic and the gear-tuning looked perfect, the sprockets were pristine and there was nothing wrong with the chain. At one point, one of the links began to widen after it got jammed and I took a link out. The bike was driving me mad, on the odd occasions that I rode it.
I took it back to the shop one day and they had a look at it and shrugged their shoulders. They could not see anything wrong with it.
At this stage I'd ridden about 600 miles with it, and done the Ring of Kerry with the usual one chain-skip every minute or so. Maddening. I'd never seen it skip as if you keep looking at the chain, you'll hit a wall.
Took it home and said to myself.. There's something wrong with the chain.
I looked at it and thought that the joining link looked a little fat. I said so to Mick Lehane, my main cycling friend and he said to clean it and it would say what speed it was for. I'd never noticed that before as I almost never used such chains.
I did. It was a nine-speed link on a 10-speed chain.
I went into the bike shop with fire in my eye and got a new chain. Problem solved. Nary a skip since. I've been onto the bike manufacturers to warn them about this. Apparently they fitted it. They're investigating the matter. This was the most difficult thing I've had to diagnose in a bike.
This is the fourth time that I've had a dangerous problem in a new bike.
I got a new Dawes Galaxy 13 years ago and the first time I pulled the front brake on a steep hill, the brake wire popped out of its socket in the brake lever, leaving me with no front brake. It'd been incorrectly assembled.
I got a Kirk Mountain bike (the worst bike ever made) with a rusty gear cable which had not been checked, and it jammed the chain, causing me to go over the handlebars while standing up, climbing.
I also got a Peugeot Mountain bike with inadequate rim tape which caused the tube in the front tyre to explode while going down a steep hill.