worker4youth

I'm hearing a clunking sound, that I can usually feel in the pedals. It happens randomly -- at any part of the pedal stroke. Sometimes it'll be quiet for a few minutes, then a loud *clunk*. Other times, it'll clunk 2-3 times (usually softer) within a pedal revolution.

I've checked the following:

- No play in the pedals
- No play in the bottom bracket. Took of the chain, and the cranks rotate more or less smoothly

I have recently converted this bike to a single speed with a chain tensioner, but that was a few months ago.

Any ideas?

FBinNY 

A few possibilities, and the nature of the clunk will be the tipoff.

Loose crank arm (either side, but usually the left) generally more of a click at first, becomes more pronounced over time if ignored.

Chain slippage on the rear sprocket. Doesn't happen on normal fixed and SS bikes, since there's no extra length in the chain loop. But can and does happen when spring chain tensioners are used. Is loud, and will feel like a pedal dropped an inch or more. Check your chain for stiff links, and stretch as you would on a derailleur bike.

A broken axle. This will click when loaded, but you rarely feel it in the pedals. This is easy enough to check by removing the rear wheel.

cny-bikeman

You may not have checked sufficiently for play in the BB. A fixed cup that is slightly loose would exhibit the symptoms you describe, but the play is not always apparent. To check, put one crank arm parallel to the down tube and grab onto it from the other side of the bike and pull firmly, bracing your other hand against the down tube. Then reverse the process on the other side. If it's the fixed cup you should be able to feel it shifting.

worker4youth

Thanks, I do see a bit of play on the bottom bracket using your method. I also see the cone is clearly loose.

gmt13

It does sound like your BB does need some adjustment but if that does not fix it, I would suspect your new freewheel. A lot of the less expensive SS/BMX freewheels make an intermittent clunking sound when pedaling. The fix is either to spend more cash or live with it.

-G

JTGraphics

I'm taking it this is not a sealed bearing remove the bearings and check them some may be cracked or not hole which at times may fill good if they are not in a bad spot so the bb may fill good till bearings are in the correct place to show the movement. Also I had a clunk caused by a cracked link plate on the chain it would clunk at times till it completely split apart. Good luck wit it.

worker4youth

I adjusted the bottom bracket, so now I am positive there is no play. Still getting noise.

I'm gonna (hopefully correctly) diagnose that this is not a BB bearing issue (yes, it's not sealed) since it's intermittent. I can sometimes go a couple miles with no noise.

Pedal / chain doesn't slip, so I don't think the chain is skipping. I'm familiar with that sound anyway.

Any other ideas? Bad chain tensioner?

By the way, try as I may, I cannot reproduce the noise off the bike.

FBinNY 

If there's no significant pedal movement, odds favor a damaged bearing. This is very common with radial cartridge bearings that are user adjustable. Users apply too much axial preload in an effort to eliminate all play. Unfortunately radial bearings aren't designed for this and suffer excess and uneven wear at the edges of the ball races. Rust is also a contributing factor.

What now happens is that the bearing seizes momentarily, but the cranks don't jam because the race can slip on the spindle or housing. I wish I could give you a proof positive diagnostic test, but often these feel fine until loaded fairly heavily. One hint may be play that cannot be resolved effectively., another may be rust colored grease weeping under the seal. On some you can gently pop off the seal and examine the condition of the bearing, but this isn't always easy.

JTGraphics

Did you actually take it apart and inspect the bearings? or just adjust, if not take it apart ad look do not assume they are good because you fill no play when you adjust it.

FBinNY 

+1, if you have any reason to suspect the bearings, the only way to know is to take them apart (pry off a seal).

Among the reasons to suspect a bearing are; high mileage/age, weather exposure, prior adjustments to eliminate play, brown grease weeping, rough feeling or noisy when spinning cranks without the chain. Any of these can point to a bearing problem, but there's no proof positive way to tell without looking at the bearing itself.

worker4youth

Took out the cone and bearings. They definitely need replacing. Thanks all!

IthaDan 

Just posting to add a gummed up freewheel with sticky pawls and loose chainring bolts to the list of possible clunks. Obviously, these two manifest differently, but "a clunk" isn't the most descriptive term.

Could also be a stiff link in the chain.

bboy314

I had a strange 'clunk' like this recently that was very hard to diagnose, turned out to be coming from the crappy freewheel.