Old tech Triumph Bicycle: Bottom bracket bearings replacement

My bicycle is from the 1970s, and is quite old. It even has a label that says “Made in Canada”, it is that old. Triumph brand. Yet its steel frame, heavy but strong, lives on. I make it live with maintenance. As with most of my bicycles, this one was used and abused by a Chinese neighbour, and then left for dead, rusted and in terrible shape. I took pity on it.

Most of the bicycle is gone. The front fork was an old side pull that was near useless, but more importantly the fork was about to snap! I replaced the front fork with one that uses a V-brake, even though it has a front suspension, which is heavy. The rear brake is still a crappy side pull. I should replace the cable and housing. Both derailleur controls and brake levers have been replaced. I think I replaced both wheels, but for sure the rear wheel is different. The rear wheel needs truing. I think I tried but need to try again, as it affects the rear brake. Seat and pedals are different. Two winters ago the rear derailleur went into the rear wheel, destroying both. Internal cable routing is cool. Some time in the future the frame will rust through and snap, but it seems ok for now.

Over last winter the bottom cranks started to become looser. I did not ride at all this winter because the gym as closed due to Covid-19. It started slowly, almost infinitely slowly, until there was a distinct sideways wiggle in the cranks. It was cold so I have waited for better weather to take the bottom bracket apart.

This is a 3 piece crank, so I needed my crank puller tool to get the cranks off. I started with a 14mm hex head to remove the hex nut, then the crank puller. The chain need not be broken, just slacken the rear derailleur, then set aside. Do both sides and remove the front gears and both cranks. There’s no need to remove the pedals.

The left side of the bottom bracket is a traditional righty tighty, so I used a thick screwdriver and hammer to loosen it off. It was on pretty tight. Out came the loose bearings and broken bits of bearing holder. All the bearing were loose and simply fell out, though some were seemly ground to dust and missing. I could not remove the right side bearing cover, but it did not matter, as I could service the right side bearing from the left.

The inside of the bottom bracket was filthy, with small bits of bearing holder mixed with dirt and grease. It was easy to clean out.

While old tech has lots of gaps and high tolerances, the good part is that I have broken other bikes down and have spare parts. Serviceable bearings in good bearing holders were easily found. Bicycles have some standardized parts. I greased the right bearing holder, bearing case facing outward, because the right bottom bracket cover had square shoulders, and the axle had rounded shoulders, for the balls. The left bearing case I put facing the middle, as it seemed to fit deeper into the axle when I put the cup on. The cup is curved for the bearings to run smoothly. Tolerances are not tight. I tightened it up enough so that the axle could spin smoothly, but not loosely. This took a bit of finessing with the retaining lock ring.

Hammering on the cranks, reinstalling the chain, tightening down the 14mm nuts finishes the job. The bottom bracket should be good for another 5 years. The sideways shimmy is now only a memory. The cleaning and install took a couple of hours, but it was a nice day and not too hot. A bit of bicycle maintenance does wonders to relax me when I’m on my own.

Ond tech

Leave a Reply

Your email address will not be published. Required fields are marked *