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Bottom bracket or pedals - how to (clunk) tell?

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Bottom bracket or pedals - how to (clunk) tell?

Old 12-01-14, 04:25 PM
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FarHorizon
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Bottom bracket or pedals - how to (clunk) tell?

Happy holidays, mech-meisters!

My single speed has a clunk when I pedal. It isn't rhythmic, like once per crank revolution, but rather random. Along with the clunk noise, I can feel the clunk in the pedals. This bike is used, and the problem came with the bike.

I've checked the chain tension - it's properly tight. I've pulled the rear wheel and looked closely at both the chainwheel and rear wheel cog - they show minor wear, but not enough to be skipping (and this doesn't feel like a chain skip, either). I also looked at the chain-line and added a shim to straighten it (the previous owner had obviously pulled the rear cog but not replaced the shims when he put it back together).

I'm suspecting that the clunk is from either the bottom bracket or a pedal. I've tried to manually "wobble" the crank arms, but they seem tight & smooth. I don't know how to go about checking the pedals for wear.

So to the question - How do I go about troubleshooting this noise? I could just do a wholesale replacement of bottom bracket & pedals (and that would probably be cheaper than paying the bike shop to diagnose and repair it), but if I can identify the problem, I'd prefer to fix just the defective component.

The crank is an FSA with the hollow, splined crank shaft. The bike is a Kona Unit that's several years old. I suspect the pedals are also original Kona. The previous owner used this as a dirt bike, but I'm planning on using it as an urban commuter.

Thanks in advance for suggestions.
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Old 12-01-14, 04:38 PM
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Originally Posted by FarHorizon View Post
...
I've checked the chain tension - it's properly tight.....
I'm suspecting that the clunk is from either the bottom bracket or a pedal. ...
So to the question - How do I go about troubleshooting this noise? ....
Just to be sure we're on the same page. ---- Proper chain tension for a fixed or Single speed bike is NO TENSION, or vestigial slack even at the tightest position (chainrings are slightly eccentric so the slack varies).

As for the diagnostic, far and away the easiest thing to do is to switch the pedals with another set. If the problem persists, it's not the pedals. If switching the pedals solves the issue, it could be either, so switch back one at a time, being sure to clean the mating faces and grease the thread.

Note that sometimes a pedal related issue clears completely simply by removing and reinstalling the pedals with clean faces on both the crank and pedal and fresh grease. So if you decide it's the pedals, but the problem disappeared enjoy your good fortune, and try the clean and grease trick next time.
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Old 12-01-14, 04:45 PM
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Thanks, FBinNY - You and I agree about chain tension - there is no slack. The chain is tight.

I'll change the pedals & hope that they're the problem. If not, then it's BB time! Thank you especially for the quick reply!
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Old 12-01-14, 04:53 PM
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Originally Posted by FarHorizon View Post
Thanks, FBinNY - You and I agree about chain tension - there is no slack. The chain is tight....
REREAD my post. We don't agree at all. There has to be slack, or zero tension at all times. A tight chain is, by definition, too tight and may very well be he cause of your problem.

Before bothering with anything else, push the rear wheel forward enough to create obvious slack in the chain (probably 1/32") is enough and see if the issue persists.
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Old 12-01-14, 05:05 PM
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Will do.
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Old 12-01-14, 05:50 PM
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Swap out pedals first, great idea. If still having clunks pull the crankset and turn the crank spindle by hand to check for rough operation. If that is a hollowtech/ISIS BB they are relatively inexpensive and easy to change out.
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Old 12-01-14, 08:27 PM
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Pedals ordered. Will add slight slack to chain tomorrow. If problem persists, should I change the BB or the entire crankset?
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Old 12-01-14, 08:29 PM
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Sounds like the pedals,,,but the chain shouldnt be too tight, too tight is not good
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Old 12-01-14, 08:54 PM
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Before spending money, do some proper diagnostic work to isolate the problem and replace (if necessary) the problem item.

A decent percentage of the time these things are resolved with no parts needing to be replaced.

Predicting which might be the likely causes depends on knowing more specific details like how old the bike is, when the problem started, and then last thing that was done before the problem started.

In the meantime, the OP has two action plans, -- move the wheel forward to slacken the chain & and swap pedals to isolate the problem. There's no purpose in trying to move forward until those are done. It would really be shame to spend money on parts when all that was needed was some simple adjustments.
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Old 12-01-14, 10:49 PM
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Originally Posted by FarHorizon View Post
Pedals ordered. Will add slight slack to chain tomorrow. If problem persists, should I change the BB or the entire crankset?
Neither. BB clicks and clunks are almost never due to a defect in pedals or BB themselves. Untension the chain first, as a non-rhythmic clunk exactly matches the problem of a tight chain (could also be bad chainline). Then go on to tighten and adjust parts properly. You don't need to order new pedals to try a different pair, either.
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Old 12-01-14, 11:14 PM
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Originally Posted by FarHorizon View Post
My single speed has a clunk when I pedal. It isn't rhythmic,........ but rather random. Along with the clunk noise, I can feel the clunk in the pedals.
That sounds like a stiff link in your chain to me.

Lift the bike and slowly pedal till it clunks. The stiff link(s) should be at the bottom/front of the rear cog. Use pliers to wiggle out the stiffness. Oil the chain and enjoy.
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Old 12-02-14, 05:09 AM
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Originally Posted by FarHorizon View Post
Pedals ordered. Will add slight slack to chain tomorrow. If problem persists, should I change the BB or the entire crankset?
As FB said (and I had inferred) hold off on the BB purchase. However, you can and should do a "finger check" of it's operation and smoothness. This will give you a feel for the internal "health" of the cartridge. The BB is about 30.00 and a tool is needed (15.00 or so). The BB may or may not be your clunk but somewhere along the way it is a good thing to check it. Your wobble test gives you a feel for tolerances and a finger twist of the spindle will give you early warning of probs to come. I'm coming up on a 4th season with my nashbar isis unit.

Just wanted to clarify a few things.
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Old 12-02-14, 10:22 AM
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Well - Good news / Bad news...

I adjusted the chain tension this morning. The chain was too tight with no play at all. It now has the slightest (⅛") flex to it.
I also watched the chain flow over the rear cog - It was smooth - I have no tight links in the chain.
I also flexed the bottom bracket again - no play that I can tell.
I also spun each pedal cage around its spindle - one was significantly harder to spin than the other.

I then rode the bike again - I still have the "clunk." Based on the experimentation of this morning, I'm suspecting that it's a pedal. I have a new pair on order that should be here tomorrow. If the pedals DON'T "de-clunk" the drive train, I'm to assume that the bottom bracket is the next stop?

I'm profoundly thankful for all the help here! I've learned a great deal just by reading your responses. Bike Forums folks are just plain awesome!
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