Thunk from the bottom bracket
08-30-12 | 11:14 PM
#1
Thread Starter
Senior Member
Joined: Jan 2012
Posts: 108
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From: Cincinnati, OH
Thunk from the bottom bracket
Ok, here's a baffler. Unknown year Azuki 10-speed (2x5) 27", with 3-piece crank.
Looking at the crank from the right side, this occurs between 6-9 o'clock, and only when high torque is applied to the pedals. And I feel it through the right pedal only, not the left (despite the torque coming from the left side at that part of the revolution)
BB is solid, no slop that I can make out. FD isn't hitting that I can tell. The front chainrings are not perfectly flat, and do wobble slightly, as does the ring guard, though I can't see anything that they may be hitting, either.
Kickstand was removed first thing, as it was my first suspicion.
So, I'm stumped. Anything embarrassingly obvious come to your minds?
Looking at the crank from the right side, this occurs between 6-9 o'clock, and only when high torque is applied to the pedals. And I feel it through the right pedal only, not the left (despite the torque coming from the left side at that part of the revolution)
BB is solid, no slop that I can make out. FD isn't hitting that I can tell. The front chainrings are not perfectly flat, and do wobble slightly, as does the ring guard, though I can't see anything that they may be hitting, either.
Kickstand was removed first thing, as it was my first suspicion.
So, I'm stumped. Anything embarrassingly obvious come to your minds?
08-31-12 | 01:27 PM
#4
Mechanic/Tourist
Joined: Apr 2007
Posts: 7,522
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From: Syracuse, NY
Bikes: 2008 Novara Randonee - love it. Previous bikes:Motobecane Mirage, 1972 Moto Grand Jubilee (my fave), Jackson Rake 16, 1983 C'dale ST500.
Overdue bearing maintenance is not going to produce a clunk at a fixed point every time, but there is a likely candidate. Fixed cups sometimes loosen enough to shift under pressure, but not enough to detect when doing the typical "is the bb loose" check. It's common to feel it mainly on the right, as there's more direct pressure on the fixed cup from that side.
Remove the right crank arm and put a wrench on the fixed cup (tighten counterclockwise). If it does move that's the problem. Before cinching it down loosen the lockring and back off the adjustable cup. Now tighten the fixed cup solidly and finally adjust the bottom bracket. Of course it can't hurt to overhaul the BB.
Remove the right crank arm and put a wrench on the fixed cup (tighten counterclockwise). If it does move that's the problem. Before cinching it down loosen the lockring and back off the adjustable cup. Now tighten the fixed cup solidly and finally adjust the bottom bracket. Of course it can't hurt to overhaul the BB.
09-05-12 | 03:39 AM
#5
Thread Starter
Senior Member
Joined: Jan 2012
Posts: 108
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From: Cincinnati, OH
Overdue bearing maintenance is not going to produce a clunk at a fixed point every time, but there is a likely candidate. Fixed cups sometimes loosen enough to shift under pressure, but not enough to detect when doing the typical "is the bb loose" check. It's common to feel it mainly on the right, as there's more direct pressure on the fixed cup from that side.
Thank you, everyone, for the suggestions.
09-05-12 | 04:57 AM
#6
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Joined: Feb 2004
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From: Thailand..........currently Nakhon Ricefield, moving to the beach soon.
Bikes: inferior steel....alas....noodly aluminium assploded
....Looking at the crank from the right side, this occurs between 6-9 o'clock, and only when high torque is applied to the pedals. And I feel it through the right pedal only, not the left (despite the torque coming from the left side at that part of the revolution).....BB is solid, no slop that I can make out.....
i'd bet it's the bearings in (one of) your pedals. hold the crank steady and try to wiggle the
body of each pedal in turn. one of them will have some play. if you remove the pedals, hold
the cage and try to wiggle the spindle, the play will be more obvious.
