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Size of replacement BB bearings

Old 05-09-21, 08:44 AM
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dfrench52 
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Size of replacement BB bearings

My bike (Nishiki Medalist) has developed an intermittent knocking that seems to originate in the bottom bracket. The sound is more pronounced at times, sometimes inaudible, always follows my pedal stroke, sometimes under seemingly light load.

Anyway...after rechecking the usual suspects such as loose chainrings, pedals or spindle endplay, I repacked the caged bearings. None of this made any difference.

The bearing races look good, the cups look good, maybe a small dark spot on the fixed cup. Since the bearings seem to be original, I thought I'd replace them with loose ball bearings. Can anyone here tell me what size bearings to buy? There are currently nine bearings per side.

Thanks!
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Old 05-09-21, 08:57 AM
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Loose balls will require 11 per side.
1/4".
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Old 05-09-21, 10:13 AM
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Many thanks, Bill.
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Old 05-09-21, 11:27 AM
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Originally Posted by dfrench52 View Post
...developed an intermittent knocking that seems to originate in the bottom bracket. The sound is more pronounced at times, sometimes inaudible, always follows my pedal stroke, sometimes under seemingly light load.
Very interested in finding out if this eliminates the knock...

I had a sound like this for years on an old FUJI and could not figure it out. When I upgraded its threaded on freewheel, the sound disappeared, but I never suspected the freewheel as its cause...
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Old 05-09-21, 03:07 PM
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Some freewheels, SunTour Perfects as example, can rock on their pawls with each turn or the wheel. Most all freewheels have some slight bearing preload slop (and this is a decades long known good thing). When the chain contact is not over the pawls (like when in the higher gears. smaller cogs) a sideways force is acting on the freewheel's outer portion (of the core). The outer core and it's mounted cogs can rock with the pawls acting as the pivots. A knock/knock that is not usually loud and seemingly inconsistent (due to cog/chain combos needed and pedal pressure amount being rather independent of each other a pattern can be hard to discern) can happen. Shift a gear or shift on the seat and the noise can go away. Another rider on your bike might not induce the noise.

Lubing the freewheel interion can change this as does a different one. Andy
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Old 05-16-21, 08:49 AM
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Originally Posted by Andrew R Stewart View Post
Some freewheels, SunTour Perfects as example, can rock on their pawls with each turn or the wheel. Most all freewheels have some slight bearing preload slop (and this is a decades long known good thing). When the chain contact is not over the pawls (like when in the higher gears. smaller cogs) a sideways force is acting on the freewheel's outer portion (of the core). The outer core and it's mounted cogs can rock with the pawls acting as the pivots. A knock/knock that is not usually loud and seemingly inconsistent (due to cog/chain combos needed and pedal pressure amount being rather independent of each other a pattern can be hard to discern) can happen. Shift a gear or shift on the seat and the noise can go away. Another rider on your bike might not induce the noise.

Lubing the freewheel interion can change this as does a different one. Andy
Looks like Andrew is on to something. Replaced the bottom bracket bearings and the noise is unchanged. There are stretches when the bike is absolutely silent save for the noise of the tires on smooth pavement. Other times I hear a knocka-knocka sound that seems to be telegraphed through the frame. No real discernable pattern as Andrew noted.

I tried lubing the freewheel (Shimano 13-28, 7-spd) with some Tri-flo and I'd like to say that the sound is lessened, and it seemed that way for a few miles. Most of time, the sound is most noticeable when using the middle sprockets.

After the ride, I put the chain on the smallest sprocket and applied some sideways pressure on the 28, noticed a very tiny amount of side play, barely detectable.

Does anyone suggest that the freewheel is defective or just doing its thing? Should I try heavier oil or try to disassemble the freewheel and re-lube the bearings? The noise can be quite loud.
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Old 05-16-21, 12:06 PM
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your bottom bracket lug might need refacing.

i had the same problem, changed from caged to uncaged bearings, new cups, new spindle, same thing.

measured the BB and found that it was off by 0.030"

that is almost 1/32" of an inch. it was like the BB never got refaced at the frame factory, they just sent it out raw.

many people will tell you that this makes no difference.

don't listen to them.

after refacing the BB, i have no more slop and no more noise.

one clue that you need a reface is that the BB will be sloppy at one point of revolution, and tight at another.

yours might be the freewheel.

does the noise make one klunk per stroke, ore multiple klunks per stroke?

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Old 05-16-21, 01:19 PM
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The axle with or without cranks spins smoothly, no evidence of binding at any point in one rotation.

The noise is multiple klunks per pedal stroke but not necessarily at the same point in the stroke. I noticed the noise disappeared after standing and mashing up a modest grade over maybe a quarter mile (52x20). But the noise returned under almost no load on a relatively level stretch in a low gear (42x24).

Shifting to high (52x13) and pedaling hard downhill resulted in noise that sounded as though the shift wasn't right. No amount of trimming the DT shifter could clean up the sound.

I don't think I have the means to check bottom bracket facing. That probably would require a dial indicator, yes?

I recently corrected the derailleur hanger that was out maybe 10mm. Shifts are better but clean-sounding shifts are sometimes hard to get.
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Old 05-16-21, 07:48 PM
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cjenrick
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sounds like your freewheel.

some are noisier than others.

i have a Mavic titanium freewheel that i paid big bucks for and the darn thing sounds like a blender full of ball bearings.
no matter how you adjust it.

check to see how much play you have between the cogs and the freewheel body.

you can remove some slop by using a screwdriver and hammer to tighten the body up.

or if you like working on stuff, you could take it apart and clean and relube.
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Old 05-17-21, 04:23 AM
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Thanks or your suggestions! I think I I'll reinstall the Suntour freewheel that came on the bike, just to see if that makes a difference. If so, I'll try taking apart the currently installed Shimano freewheel and clean&relube.

I really need that 28 tooth low on the Shimano. Hate to toss the freewheel.🙄
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Old 05-18-21, 12:30 PM
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Put the original Suntour freewheel on and: Perfection. No knocka-knocka in any gear, under heavy load or or no. Thanks for all of your suggestions.
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