Arthurpwiggle

My bike recently started "catching" at the same spot in the crank. It's like a little bump on each revolution. Does not appear when on the rack. If I pedal past it, back pedal, then pedal past it again it does not appear. Only happens on full revolution regardless of gear on rear cassette.

Any ideas?

Bill Kapaun

Always the same arm?
Slowly spin the pedals with your fingertips to check for initial roughness there. Compare the 2.

Drop the chain off the rings and mount the bike leaning against the wall. See if you can isolate it to the BB.

You might mention what kind of bike/drive train you have. That way we can avoid guessing at impossibilities.

Arthurpwiggle

I can feel it in both arms, but if I had to pick one, I'd say right.

This is a Diamondback Hanjoo Metro with a no-name single cog crankset and Shimano Acera RD-T3000, 9 Speed derailleur in the back. Bike is 2 years old, regular commuter (about 3x per week on average).

I just dropped the chain and spun the pedals as suggested.

Spun the pedals - smooth as silk
Spun the bearing - smooth as silk

However, if I put lateral pressure on the crank arm when spinning it I can make it catch. (meaning if I pull outward while turning the crank, I get the catch, and it catches harder the harder I pull outward)

I'm starting to think I have a bearing going bad in the bottom bracket. Do you think a clean an re-grease might fix this issue or does this sound like a bracket replacement?

Iride01 

I was having a similar issue, always when putting out power and same crank position. I thought the BB too. Pedals felt smooth when spun by hand, but since I had another bike with the same pedals I swapped them out just to be certain before changing out the bb and the bump went away.

Crankycrank

Also check that your chainring bolts are all tight.

Bill Kapaun

It appears that has a sealed BB, so just replace the cartridge.
Typically, the DS bearing gets more wear since it has forces from 2 directions acting on it.

Arthurpwiggle

OK, stupid newbie question time.

How do I find the correct cartridge to purchase to replace it? I've never removed a bottom bracket before.

bakerjw

Do you have the tools to remove it? While it can be done without them, they really help.
Once you get the BB out, it will likely have some markings on it. If it is a square taper, measure the BB crank axle and look for one similar in length. I had to do that for a tandem build a few years back.

Arthurpwiggle

I do have the tools. I don't have a torque wrench, though the YouTube videos I've watched lead me to believe that is it unnecessary.

I'm most concerned about identifying the correct replacement part and understanding if I have an option of upgrading the part or if it's best to just stick with the same part.



I keep hearing the term square taper but I'm not sure what exactly that means. Also, when you say measure the crank axel, you mean the length from where one crank arm attaches to the other, or the width of the BB casing?

I'm in Japan, and my best bet is to order online, I don't want to order the wrong part multiple times before I get to the right one.

Bill Kapaun

If you can't find the spec from online docs for YOUR SPECIFIC CRANK, you'll pretty much stuck with trial & error.

IF you measure your chainline, you can determine how far off you are and then adjust to the size marked on the existing BB.
You still might be a size off, but "usable".

Kapusta

You sure it is not a pedal? Have you tried swapping for a different set?

JohnDThompson 

The most reliable way is to pull out the old one and match its part number.

Failing that, post your crank (make, model, and configuration: single ring, double, triple) and perhaps someone can help.

Iride01 

You ought to take this to a bike shop and let them find out what's up. A bad bb in two years is unusual. I've never had a bad bb.

You don't have to let them fix it. But you'd be back on a properly running bike quicker.

Trinity Pratt

Before you take your bike apart, listen to the guys saying try different pedals. Had one just recently behaving like that. First thought like you, oh man, what's wrong with my BB? But did change the NDS pedal (that's where I was feeling it) and it went away. Later looked at the pedal, there was an allen wrench socket, tried turning that (tightens the release tension or something) and retried the pedal. Bump gone.

CliffordK

Have you replaced any other parts recently, like a new chain?

It is possible badly worn rings would cause a new replacement chain to climb off of the rings.

Arthurpwiggle

I'll give it a try. It's worth a shot.

Arthurpwiggle

Haven't replaced anything else except a couple spokes.

Arthurpwiggle

So, I finally got a chance to change the pedals. That did not solve the problem. I was able too get the information on the bottom bracket, but I don't know how to decipher it. Any help with how I ensure I order the correct replacement?

Google only got me part way there.

SRAM
BB-GXP-A1
00.6418.001.004, BB GXP XR TD MTB73 ROAD68

Trevtassie

Looking at the pictures of your bike and the cranks it looks like a square taper. Whip it out, measure the length, order the nearest Shimano UN55.

Arthurpwiggle

I really appreciate everyone's help. I've got is narrowed down to either the 68x107mm or 68x110mm UN55. I have not taken off the cranks but I did some measurements of the BB with calipers. Near as I can estimate, the current bracket is right around 68x108mm. If it were you, would you go for the 110 or the 107?

Bike Gremlin

If I had to guess (no chance of measuring and/or no chance to try which one fits best), I'd go with the 110 mm spindle version.

Apart from the cranks hitting the frame (in case of being too close - too short BB axle), thing to consider is chainline.

Arthurpwiggle

Just wanted to close out the thread by saying that it was in fact the BB. I got it replaced and the problem is gone. Thanks for everyone's input!