How can I remove a stuck bottom bracket cup?

Question

I am repairing the bottom bracket of a US$100 bike with hard 2,000 miles (3,200 km). At approximately 1,800 miles (2,900 km) the bottom bracket made a crunchy sound, and after that there was a lot more play and friction in the bottom bracket.

I removed the cranks:

After opening the bottom bracket, I found that the bearings need to be replaced:

I removed the cup on the left side:

I was unable to remove the cup on the right side. The cup on the right side is not seated squarely in the frame. One side of the cup touches the frame, and the other side of the cup is 2.4 mm (0.094 inch) away from the frame:

I tried unscrewing in both directions using a maximum of 120 ft-lbs (160 N⋅m) on the wrench, but it didn't budge.

Another factor in this equation is wear on the spindle:

I have identified these options:

1. Install new bearings without trying to remove the cup.
2. Press the cup in so that it is square with the frame. I'm not sure if the cup is threaded or press fit, this would work better if it were a press fit.
3. Use more force to remove the cup.
4. Cut the cup out and replace it with a sealed bottom bracket.

To proceed with the repair I need to answer the following:

• How important is squareness of the bottom bracket cups?
• Is there a trick for fixing cross-threaded bottom bracket cups?
• Are the grooves on the spindle too deep to function with this size bearing?

Answer 1

You're going to need to replace the entire BB.

The drive side cup is reverse threaded. (This isn't true of older bikes of certain nationality, but the nylon cable guide suggests yours is new enough for this not to be a concern.)

To answer your questions:

• The squareness of the cups is very important for the BB to function.
• To get the cup out without special tools, there's a few things to try depending on what's available to you. It would be a good idea to soak in some penetrating oil, just because anything you can do to reduce the torque required will help. If possible, clamping the wrench flats on the cup in a bench vise and using the frame as your leverage might be the easiest way to get it started. Another approach involves making a fixed cup removal tool out of a large bolt, nut, and washers, as explained by Sheldon Brown. This sort of tool usually works very well even on the most stuck cups, and is cheap to put together.

• After you get the cup out, you'll have to address the condition of the threads, i.e. is some kind of thread repair going to be necessary to get the new BB in. More minor examples of cross threading, like where a cup got started cross threaded, usually don't require anything special here, but what you have could be pretty chewed up. Presuming you're replacing with a cartridge, probably the first thing to try is, after cleaning and greasing the threads, try to start installing it by hand (ie holding on to the splined installation tool) and, looking at it from the left side, keep it visually centered in the shell as you push with the tool, even as it wants to wander off axis. It may be rough starting and will probably go in rough, but that's not a dealbreaker as long as you can get good enough thread preload in the end.
• All traditional cup and cone BB cups are made of hardened steel. If doing some repair of the threads is needed and paying a shop to just run a tap through it isn't in the cards, getting an old scrap fixed cup to use as a rudimentary chasing tap is something else you could try. (The one you have is likely too mangled for this). Doing the same with whatever new cartridge BB you get isn't necessarily a good idea because it might get damaged.
• I'm not entirely sure what you mean about the grooves on the spindle, but that spindle is too mangled to be put back in.
• Pressing on the cup would probably damage the threads further if it does anything, which it likely won't. Trying to just notch it over into place isn't going to work. To my awareness, this kind of thing happens when someone at the factory is going too fast with an impact tool.
• Cutting it out down the middle given the hardness of the material and how easy it would be to cut into the frame threads is probably not very realistic.

Answer 2

Nathan's answer covers it all, but to expand on the last point... That cup is dead.

Your last resort is to cut the cup out - I've done it once. In my case the bearings had failed, and the rider was rubbing the BB axle on the cup directly, slowly eroding through the casting.

The cup would not turn even using the correct BB cup wrench a park HCW-4

You can see the fresh tearing on the right side, where the wrench has peened over the hardened steel.

I tried penetrating oil, brute force, hammering on the pictured tool both in the correct and wrong directions.

In the end I used a medium toopth hacksaw, fed the blade through the hole and refitted to the hacksaw frame. This allowed me to cut downwards not upwards or sideways. Also it was the worn-thin part of the cup, but later I realised it was probably work hardened too. It probably took 90+ minutes of hacksawing over a couple days to get mostly through it.

When I got near the end, there was risk to the threads in the frame. When I could see the saw marking the blue frame paint through the cut, I stopped hacksawing and tightened the cup into the frame. This was enough pressure to collapse the cup enough to slowly unthread it completely.

The threads in the frame looked okay, and I should have used a BB thread chaser to restore them but don't own one. Instead I cleaned them of dust and grease and grime, and used a sharp pick and a heavy wire brush to scrape through the threads to clean them.

I fitted the cheapest cartridge bottom bracket available, and it took a lot of torque to get in even with assembly paste. Chasing the threads would have made that easier - I suspect that cartridge will never come out.

Next time I would use a small rotary tool (dremel) with a cutoff disk or perhaps a burr to cut through the cup, and not a hacksaw.

Answer 3

I'm going to offer the unpopular answer: just replace the bike.

At $100 and a hard 2000 miles, that bike doesn't owe you anything. And if the cap is tweaked like that, it was probably cross threaded, which means it might be permanently damaged during installation. This would explain why it's so hard to remove, since the assembler at the manufacturer simply kept screwing it on at an angle with an air tool, instead of backing it out and trying to get it in straight.

Also, the parts to fix this might cost more than the bike. Even the bearings that look good probably need replaced, since you want new bearings to wear into your other new parts, instead of the current cheap sets.

I'm totally a DIYer and would have done exactly what you did to try to fix the bike, but even so, you have to consider when it's worth your time and money. With a cross threaded part in a critical location like that, you'd have to fix the threads, yet there's no good way to do that with that thin a piece of metal. You can't just use a insert threading kit, since that relies on the strength of the surrounding metal, which you might not have. And good luck finding the size, and possibly left hand thread, you need. The other option is to add metal back on, and welding or even brazing that thin of metal has a good chance of warping it, even if you had a tap that size and direction to recreate the thread.

What Criggie suggested about cutting out the cup can take a lot of time and effort, and if the threads are as bad as they could be from cross threading, it'll be wasted. I've seen things that cross threading had sheared off the threads (not on a bike), to the point where it was metal spaghetti coming out. And yes, that's on a completely stuck part that required major effort to remove. And the hacksaw is the best way to cut that out. A Dremel-style tool won't get the the straight cut in the direction needed. And a saws-all is way too aggressive, with the likelihood of damaging the frame high, not the mention the threads.

Also, with it being a hard 2000 miles on a $100 bike, you are likely in for more repairs real soon. Unfortunately, that's what you get for a bottom rung quality bike. I've owned several bikes like that when I was younger and I did a lot of repairs.

Normally, 2000 miles on a bike isn't much of anything and you shouldn't have to do repairs yet, but with them being hard miles and something just goes "crunch" one day, then you not fixing it for another 200 miles, that's a recipe for more problems, sorry to say. You don't know what other stresses you put on other parts to compensate for the broken parts. You already have to replace the spindle because of that excess wear, so there's likely other things that have more wear because of this, too.

And those bearings you know you need to replace shouldn't look like that after 2000 miles. There's no reason the crown/race should be that dirty.