It's been nearly two years since I Bafanged¹ my very old (circa early 1970's) Raleigh road bike, and it has honestly been good as gold since. The sum of the maintenance over the past two years has been:
Really not bad for a bike from the 70's that is ridden at least 15km nearly every day. Most of that is down to the fact that bicycles are incredibly simple things, with really not all that much to go wrong.
So with that said, I recently went for a spin into the hills of Howth, which are very well known by the lycra-wearing Dubliners, and much to my embarrassment, found that my chain was slipping pretty severely on the hills. Not ideal when you're trying to look cool while overtaking Middle-aged men in Lycra on the hills.
Initially I thought that perhaps the nylon gear in the motor was the culprit because it was only slipping when running the motor. However, after applying some actual torque to the pedals myself, I could reproduce the issue, ruling out the motor.
Next, I checked the chain, and found that it was surprisingly loose. The rear derailleur is responsible for tensioning the chain. Here's a terrible diagram of roughly how it works:
In my case, the pulley cage was seized, and the tension from the spring was not sufficient for the t-pulley to tension the chain.
A healthy dose of WD-40 and a good clean with a micro-fibre cloth to clean out the area did the trick. I then worked the pulley cage over and back for about a minute and then applied a small amount of chain lube at the pivot point to help reduce friction. A nice easy fix.
So why did this actually happen? The answer is most likely poor maintenance on my part. I have actually been relatively good at lubricating the chain on this bike. I use wet lube, which is designed for wet weather conditions⁴. This means that it won't get washed away when riding in the wet, but it also means that it attracts more dirt and grime to the chain. I have also in the past been guilty of (1) not sufficiently cleaning down the chain between applications, and (2) applying too much lube.
This combination of errors on my part likely caused dirt to build up in the pivot point and prevent the pulley case from moving, preventing the chain from being tensioned and most importantly, causing embarrassment for me on the hills. Serves me right, lesson learned.
¹ The Bafang BBS02 to be precise ² If you're interested, I got a set of Panaracer Pasela ProTite in the weird 27 x 1-1/4 size that British road bikes of this era use. I think they're pretty good? ³ The structural integrity of the old rim was compromised from a previous bike crash many years ago and it finally gave in ⁴ I know there's a big old debate to be had about what chain lube to use, and that I probably should be using some other chain lube or whatever