The next stuck part on the Trek was the bottom bracket. This is going to be a long blog post so here’s the summary: the adjustable cup was rusted in place, and it took a bunch of penetrating oil, several tool purchases, one broken tool, and a propane torch to remove it.
What’s a bottom bracket?
The bottom bracket is the thing the pedals revolve around. The pedals connect to arms, and the arms connect to a spindle that goes through the bottom of the frame. Imagine what the first bottom bracket might have looked like or, if you like, what a five year old would use for a bottom bracket. The frame is a bunch of metal tubes welded together. At the bottom of the bike, four tubes some together: the seat tube (the tube that the seat post slides into), the down tube (the one that goes diagonally from the front of the bike to where the pedals are), and the chain stays (the tubes that go from the back wheel to where the pedals are).
A simplistic model of a bottom bracket might be a solid piece of metal with a hole going through it. A metal spindle — say, a simple cylindrical rod — goes through the hole, and a crank arm attaches to each end of the spindle. When you spin a pedal, the spindle rotates about its axis, which causes the other pedal to spin as well.
You wouldn’t want the spindle to wiggle around so you’d want the hole to be just big enough to slide the spindle through. Except if you wanted it to rotate, the hole would need to be a little bigger than that; otherwise friction would get in the way. With enough grease, that might sort of work.
In early 1980’s, when my Trek was made, the solution to the friction problem was called a cup and cone bottom bracket. There is still a metal spindle at the bottom, but about a third of the way from each end, it flares out to form a circular ridge. That part is called the cone. And instead of being a solid piece of metal, the bottom bracket is mostly hollow, but with circular caps that screw in at both ends. The caps curve in from the inside. Whereas the cones are convex, the caps are concave. They fit together but don’t actually touch. Sitting between them are a bunch of ball bearings, about nine on each side, sitting in lots of grease. When the spindle turns, the cup spins against the ball bearings.
The Trek’s wheels also used a cup and cone design but I’ll leave that for an other blog post.
If you wanted to keep your bike in shape, you needed to take your bottom bracket apart every few years, clean it out, and replace the grease and ball bearings. Later on, someone invented a sealed cartridge design, where the bearings, grease, and most of the spindle were encased in a sealed metal unit.
As far as I can tell, cartridge bottom brackets work at least as well as cup and cone models, but they last longer and don’t require periodic maintenance. That’s what I want for the Trek.
Pin Spanner
It turns out there are a plethora of bottom bracket tools, each specialized to a particular type of bottom bracket. I think you could spend several hundred dollars on bottom bracket tools alone.
Removing the fixed cup wasn’t hard once I had the right wrench: slip the wrench around the fixed cup, bang the handle with a rubber mallet, and out it came.
The adjustable cup was another story. There is no way to wrap a wrench around it. Instead, there are six small pin holes. You slip the ends of a pin spanner tool into to of the holes, rotate the adjustable cup, and it gradually unscrews from the frame. After it unscrews enough, you can unscrew it the rest of the way with your fingers.
At least that is how it works when the cup isn’t rusted into place. As it was, when I tried to turn the pin spanner, it twisted until the pin popped out of the hole. Holding it in place with one hand and twisting with the other didn’t help.
Pin spanner with washers
It seemed like I needed a better way to hold the pin spanner against the adjustable cup. If I could keep it from slipping out, I might be able to twist it hard enough to force something to move.
The spindle protruded from the hole in the adjustable cup, and at the end of the spindle was a hole for a large bolt. I bought some big, thick washers from Home Depot, stacked them up around the spindle, and then bolted them down like this:
After that I could pull harder on the pin spanner but still nothing moved.
Ordering a bottom bracket wrench
I decided to try a heftier wrench. There are six holes in the adjustable cup. Surely there had to be a tool with six pins arranged in a circle, one for each hole. I looked around for a tool like that. No one in the United States seemed to sell one. A website in Belgium advertised what I was looking for but they didn’t seem to be selling them.
There was also this tool from a British online bike shop:
It looked promising but neither the bike shop nor the vendor, Royce Engineering, seemed interested in sharing the dimensions of the tool, so I couldn’t tell whether it would work for me.
Giving up on finding a six-pin wrench, I considered a two-pin wrench. If two pins seemed weaker than six, at least a solid-bodied wrench would be stronger than a pin spanner. Park Tool had the HCW-4 for $31.95. That seemed like a lot of money, and none of the local bike shops seemed to have one. Rivendell had a less expensive model: not as hefty at Park Tool’s but still better than the pin spanner. I ordered one and waited for it to arrive.
The Rivendell ended up shipping the wrong tool. I emailed them about about, and they said they’d ship the right tool but a few weeks later, it still hasn’t arrived.
The expensive wrench
I eventually bought the Park Tool crank and bottom bracket wrench. To improve my odds, I used the same washers I used last time to hold the wrench against the bottom bracket. The pins broke right off.
You can buy replacement pins for the wrench so at least I didn’t eat the entire cost of the wrench. I ordered four more pins and waited for them to arrive.
Torch
While waiting for the replacement pins, I tried another tactic I’d read about: a torch. The advice was mixed: some people recommended heating the bottom bracket itself, while others recommended heat the frame surrounding the bottom bracket. I alternated between heating with the torch and then rapid cooling with ice.
Eventually, after five or six times, I managed to break the bottom bracket loose.
The torch burned the paint around the bottom bracket. I’ll have to scrape that off and repaint it so it doesn’t rust.
Bike Coffee Taco 