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Bearing Size

Old 06-20-22, 04:10 AM
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rodscot
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Bearing Size

The bottom bracket bearings on my 3 year old grandaughter's kiddie bike have disintegrated. Can anyone tell me what size the replacements would be. Or tell me how to measure them. There is nothing left of the original bearings to actually measure though.

I have a thread on here of when I had to sort out her rusted chain. And here are some pics:





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Old 06-20-22, 04:26 AM
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Without seeing it in person I’d guess this is the “juvenile” size 1 piece bottom bracket:

https://www.modernbike.com/sunlite-m...racket-cup-set
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Old 06-20-22, 04:03 PM
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Originally Posted by rodscot View Post
... There is nothing left of the original bearings to actually measure though.
When you opened up the bottom bracket, were there any balls remaining? I can see the cages getting chewed up and unrecognizable, but ball bearings would be hard to destroy or even deform.
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Old 06-20-22, 05:42 PM
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Not sure if this is relevant for your granddaughters bike but check this article. One-piece ("Ashtabula") Cranks (sheldonbrown.com) If you have any bike shops nearby they could probably tell you and bearing balls are cheap, even at bike shop retail prices. Just bring in the crank and races.
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Old 06-20-22, 09:33 PM
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99% chance they are 1/4" balls
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Old 06-20-22, 10:03 PM
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^This^
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Old 06-21-22, 01:48 AM
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Thanks, Crankycrank. I saw that Sheldon Brown article.

Mudpie - there were balls remaining. The cages were destroyed but there were 14 balls. Which seems an odd number. So there may be some missing. The balls were 8mm which seems to cnvert to 5/16".

I have ordered a couple of 5/16" bearings with an outer cage diameter of 38mm. The diameter would seem to fit the shell. So I will see how I get on with that.
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Old 06-21-22, 06:23 AM
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Originally Posted by dedhed View Post
99% chance they are 1/4" balls
Being an American 1 piece bottom bracket, they should be 5/16” balls.
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Old 06-21-22, 07:47 AM
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Isn't that bike getting pretty small for her at this point?
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Old 06-21-22, 08:34 AM
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Originally Posted by smd4 View Post
Isn't that bike getting pretty small for her at this point?
Errrm, not sure what you mean? But no. It was her sister's and was in one hell of a mess when it had been left in the rain. I worked on it last year to make it ready for the wee one when she was big enough. So she started to use it not that long ago. She is coming up for 3.
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Old 06-21-22, 09:36 AM
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Originally Posted by rodscot View Post
...

I have ordered a couple of 5/16" bearings with an outer cage diameter of 38mm. The diameter would seem to fit the shell. So I will see how I get on with that.
Good that you had existing bearing to measure.

I assume you could install the bearings without cages, too. Cages make it easier, but the grease will retain the balls during assembly and installation.
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Old 06-21-22, 12:18 PM
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Originally Posted by MudPie View Post
Good that you had existing bearing to measure.

I assume you could install the bearings without cages, too. Cages make it easier, but the grease will retain the balls during assembly and installation.
It would be really tricky, I think, Mudpie because of the one piece crank. But I didn't think of trying that.
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Old 06-21-22, 05:51 PM
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Originally Posted by MudPie View Post
Good that you had existing bearing to measure.

I assume you could install the bearings without cages, too. Cages make it easier, but the grease will retain the balls during assembly and installation.
It's been my experience that fully loose balls in an "Ashtabula" type BB don't hold their place WRT the other balls and the ball tracks on the cone and cup. I suspect it has to do with the bearing load/contact angle, the size of the balls for the above and the amount the cup and cone "cradle" the loose balls. 1 piece BB's have fairly shallow cups and cones that are often conical and not 3D curved. Still trying fully loose balls will be a good exercise in learning and working with stuff. If it works with the parts you have that's great. Andy
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Old 06-22-22, 05:02 AM
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Originally Posted by Andrew R Stewart View Post
It's been my experience that fully loose balls in an "Ashtabula" type BB don't hold their place WRT the other balls and the ball tracks on the cone and cup. I suspect it has to do with the bearing load/contact angle, the size of the balls for the above and the amount the cup and cone "cradle" the loose balls. 1 piece BB's have fairly shallow cups and cones that are often conical and not 3D curved. Still trying fully loose balls will be a good exercise in learning and working with stuff. If it works with the parts you have that's great. Andy
There is another issue with the one piece crank. There does not appear to be a 'proper cup'. The nut and washer screws onto the crank and not into the frame. So, I am not sure how the crank and bearings would be held in place?
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Old 06-22-22, 06:45 AM
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Old 06-22-22, 07:53 AM
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Originally Posted by rodscot View Post
There is another issue with the one piece crank. There does not appear to be a 'proper cup'. The nut and washer screws onto the crank and not into the frame. So, I am not sure how the crank and bearings would be held in place?
The pressed in cup (the silver thing in the BB shell that also is securing the white chain case inner piece) is as proper as it needs to be. What can be confusing is that the relative parts are in an different order when compared to a threaded shell running a loose ball BB. Andy
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