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Old 10-27-09, 12:33 AM   #1
vredstein
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School me on BMX hubs

I'm an experienced road bike and commuter bike mechanic. I've worked in a few shops and have a good touch setting things up. But I have no BMX riding experience, no BMX shopping experience, and I don't know the little ins and outs of the bikes.
I'm working on a customer's bike now. It's a Diamondback Joker. He brought it in for a simple tube change, but I felt a LOT of play in the rear hub. After disassembling it, I found it uses a bunch of small 1/8" balls. The balls were shot, I mean chewed up, the cones and races were also shot.
My question is, why would they use such small balls in a BMX hub, a hub that's designed to get abused, jumped, jolted etc. Is this just something they put on cheap OEM wheels?
What are the standards for hub axles. I didn't have a pair of calipers, but this appeared to be between 13 and 14mm. Replacement wheels seemed to come in 14mm, so I assume this is one of the standards.
Does anyone know of a good website that is a good source for this type of information?
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Old 10-27-09, 07:03 AM   #2
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That's an unsealed hub, and yes those are just cheap ones that they throw on the bikes in production, because overall its a pretty cheap bike.
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Old 10-27-09, 08:05 AM   #3
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That's an unsealed hub, and yes those are just cheap ones that they throw on the bikes in production, because overall its a pretty cheap bike.
It seemed strange because the hub was laced to a Sun Ditchwitch rim. When I was looking at replacements in the J&B catalog, they offered wheels with sealed bearings laced to these same rims, and the wheels were mid to high range in price.
Also, the old hub was filled with loose balls, not even caged bearings. Usually, the reason for using caged bearings is that it's cheaper to manufacturer hubs this way, just popping in two cages versuse placing in all the individual balls.
Either way, I'm hoping the customer will be willing to get a good quality wheel. If the frame fits him, higher quality components set up properly can run much better than a high end bike set up poorly.
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Old 10-27-09, 11:00 AM   #4
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Generally, most bmx hubs come in two sizes. 3/8 and 14mm. 3/8 is about the o.d. of a pen and 14 is the o.d. of a fat marker. For overhaul help, check the Park Tool website. Here is a direct link to fixing cup and cone hubs that you are working on.

http://www.parktool.com/repair/readhowto.asp?id=105

I do have to ask one thing. If the customer asked for a tube change, why do you have the hub taken apart? Should the customer be made aware of the problem before fixing it?
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Old 10-27-09, 02:18 PM   #5
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The loose balls are how an unsealed hub is set up. The cone on the inside, coated in grease, holds those bearings in there.
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Old 10-27-09, 07:34 PM   #6
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Generally, most bmx hubs come in two sizes. 3/8 and 14mm. 3/8 is about the o.d. of a pen and 14 is the o.d. of a fat marker. For overhaul help, check the Park Tool website. Here is a direct link to fixing cup and cone hubs that you are working on.

http://www.parktool.com/repair/readhowto.asp?id=105

I do have to ask one thing. If the customer asked for a tube change, why do you have the hub taken apart? Should the customer be made aware of the problem before fixing it?
I noticed the hub was really loose, adjusted it, still noticed roughness, then took it apart to have a look. The customer won't get charged for anything but the tube change, and be advised on the condition of the hub. I haven't fixed anything but the tube yet. I do these things on a case-by-case basis. If I had a full load of work with other bikes, I probably wouldn't have taken the time to take the hub apart.
I have lots of experience overhauling mtb and road hubs, most use 1/4" in the rear. I wasn't sure if 1/8" balls were common, or whether the customer might have just put them in himself because he had them lying around.
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Old 10-28-09, 05:59 AM   #7
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If you have any of the same size balls laying around your shop, you should put those in with the original ones if they'll fit. That way, even though he's riding an unsealed hub, it will roll smoother. A fresh coat of grease should help too.
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Old 10-30-09, 04:27 PM   #8
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I would guess that the reason for the small bearings is that the hub is designed for a smaller size (13-14 tooth) BMX-specific freewheel. Since the FW has a smaller diameter, the bearings have to be smaller to fit in the hub. If the hub is a flip-flop, it likely has bigger bearings on the side that takes a 16+ tooth FW.
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Old 11-01-09, 04:24 PM   #9
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The freewheel takes a four-notched removal tool, larger than the four-notched tool I have in the tool kit. I'll take another look at the model, but I suspect you're right, it's a BMX specific freewheel. I was surprised when I called DB and found out the bikes only come with a 90-day warranty. The customer says they purchased the store's extended warranty, and since I'm new to the store, I'm still figuring out to make a claim.
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Old 11-03-09, 02:13 AM   #10
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Is this just something they put on cheap OEM wheels?
For the most part, yes. You'd be hard-pressed to find a aftermarket hub with unsealed bearings, with the exception of some freecoasters, which are high-maintenance, anyway.
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Old 11-03-09, 07:55 AM   #11
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which are high-maintenance, anyway.
Mines not too bad. just a little tweaking in the slack every now and then to get it to feel just right.
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