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Discussion Starter · #1 ·
I noticed that whenever my left foot goes through the 1 o'clock position (looking from the left side of the bike) I feel something like a very, very small, "skip" in the pedal rotation. The skipping occurs always in the same spot whenever I'm pedaling. At first I thought it was a loose BB or damaged bearing. However, if I spin the cranks by hand I don't feel any skipping. Someone suggested that the culprit might be my rear cassette or an uneven pedal stroke. Any comments?
 

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NeoRetroGrouch
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trainCatcher said:
I noticed that whenever my left foot goes through the 1 o'clock position (looking from the left side of the bike) I feel something like a very, very small, "skip" in the pedal rotation. The skipping occurs always in the same spot whenever I'm pedaling. At first I thought it was a loose BB or damaged bearing. However, if I spin the cranks by hand I don't feel any skipping. Someone suggested that the culprit might be my rear cassette or an uneven pedal stroke. Any comments?
My guess is that it's your pedal stroke. Shift up a few gears (this is not the fix!) and it goes away, right? Think circles. - TF
 

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Every little counts...
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If it happens on the same position of the pedal stroke, it probably has nothing to do with the cassette.

Your crankarm is loose, or cleat/pedal. Clean, lube, and re-install the BB to spec.
 

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Arrogant roadie.....
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bikeboy389 said:
Sounds like a loose crank to me.
...probably so loose that it's galled the crank arms and shaft, and they'll all need to be replaced.
 

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Zeppelin/Ultegra Rider
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Another possibility

trainCatcher said:
I noticed that whenever my left foot goes through the 1 o'clock position (looking from the left side of the bike) I feel something like a very, very small, "skip" in the pedal rotation. The skipping occurs always in the same spot whenever I'm pedaling. At first I thought it was a loose BB or damaged bearing. However, if I spin the cranks by hand I don't feel any skipping. Someone suggested that the culprit might be my rear cassette or an uneven pedal stroke. Any comments?
What pedals are you running...I had a similar feeling toward the end of last year. My (old-style) Look's just needed a bit of grease in the needle bearings.
 

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trainCatcher said:
I noticed that whenever my left foot goes through the 1 o'clock position (looking from the left side of the bike) I feel something like a very, very small, "skip" in the pedal rotation. The skipping occurs always in the same spot whenever I'm pedaling.
Check your pedal bearings, try a different pair of pedals/shoes on the bike.
 

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Discussion Starter · #8 ·
I appreciate the feedback. I'm using Ultegra pedals, but they are brand new and seem to turn smoothly. Also, the BB does not feel loose when I try to move it around with my hands. It is possible that things change as the frame flexes when I pedal. I had problems with the BB before, but the shop lubed and tightened it a couple months ago. The skipping appeared recently. I will try playing around with my pedal stroke and see I can find some correlations. I've moved my saddle around recently so maybe my stroke changed inadvertantly as well.
 

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Discussion Starter · #10 ·
I have the Cannondale Synapse carbon with Cannondale Si cranks with integrated BB. The bike is only three months old. The BB got slightly loose when I first got the bike and would creak when pedaling hard. The shop relubed it and the creaking went away.

So I tried playing around more with my pedal stroke. It does seem that the skipping goes away if I work hard to make "perfect circles" or am riding at higher speed. This does seem to fall inline with Turtle's prediction. I think I finally understand how my pedal stroke could lead to "skipping". My rear hub (Mavic) has quite a bit of play between its internal "teeth". Meaning, I need to turn the cranks in reverse a noticeable amount to hear the clicks that signify a new tooth has been engaged. If I move the cranks backwards by this tiny amount (before a new tooth is enganged), moving the crank forward will not spin the wheel until I return to the original spot.

I can imagine how this effect can lead to the illusion that my BB is skipping if my pedaling is not completely smooth. I'm not 100% convinced that this is my problem, but it definitely seems like a partial solution. It's just odd that this "skipping" only seems to occur on my new road bike and not on my mountain bikes. Strange.
 

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Discussion Starter · #11 ·
Mystery Solved

On my ride today, the "skipping" got much, much worse. The left crankarm had noticeable play in it, so I immediately took the bike to the shop. It turned out the glue that attaches the carbon crankarm to the BB connector gave out. The shop is swapping out the arm. Well, I guess my pedal stroke wasn't the problem.
 

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Hmmmm

trainCatcher said:
On my ride today, the "skipping" got much, much worse. The left crankarm had noticeable play in it, so I immediately took the bike to the shop. It turned out the glue that attaches the carbon crankarm to the BB connector gave out. The shop is swapping out the arm. Well, I guess my pedal stroke wasn't the problem.
Amazing that you weren't able to tell this earlier - grabbing the crank arm and giving it "the 3-D wiggle" seems like it should have been obvious. Oh well, all better now.
 
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