My quick description how I wrestled with Shimano bottom bracket in order to replace bearings rather than spending money for new cups/bearings set.

The story began with BB-4600 which seems to be fine for 6 months, and then suddenly, at one evening after ride I realised that whole drivetrain is not spinning freely as it should. Quick inspection revealed that component which apparently should be quite robust died quietly. Left bearing in bottom bracked spins but with grinding feeling. After quick calculations was obvious that I need another one in order to keep my wheels rolling. Eventually decided to make a small experiment. I decided to replace bearings in old cups, and slightly upgrade them in the same time.

Step 1: Find Decent Bearing!

The first step was to find out what size of bearing I'll need. After quick measuring/googling I realised that Shimano makes life hard for those who wants replace just a bearings. The problem is simple. Almost impossible to buy (decent quality) bearing in size 25x37x6mm, but it's broadly available bearing 6805-2RS (sometimes known as 6805-RD) which is 25x37x7mm. I've decided to buy set of ceramic bearings from China trough ebay, as I wasn't sure about result of the whole operation. They cost me £20 including postage so not too bad price after all for (semi)ceramic bearings. I've clicked "Pay" in PayPal and the fun begun.
<p>I think it is not necessary to use special <br>tools made by yourself, I managed to disassemble this cartrige with <br>steel hammer and flat screwdriver as it was shown on this video:</p><p>https://www.youtube.com/watch?v=fT0cRpDzhqk</p>
<p>i found a actual same size 25x37x6mm ceramic bearing from china and waiting shipment only. in this case. do i still need to do your step 4 modify the seal or i can just direct used back the original seal after new bearing install ?</p>
<p>do you think just replace the bearing ball to ceramic ball instead of replace the entire bearing ? </p><p>what is the ball size ?</p>
<p>I'm not sure what is the ball size. AFAIR was about 3mm? but I might be wrong. I'd say replacing just a balls will be quite tricky. I'd love to see if you can do it. The other thing is, I don't remember which direction the bearings are fitted you probably will need to remove them anyway. If I'll find old bearing I will ping a post with dimensions (google it?). Cheers</p>
Hi, <br> <br>Great write up - I've taken apart the bb to regrease the bearings (in spite of the Do Not Disassemble), but want to do a bearing replacement as well. Few questions: <br> <br>1. did the use of a 7mm bearing cause any problems? Did you just push the bearings in 1mm more, which left them with no gap ? <br> <br>2. did the ceramic bearings make a difference when riding or would you go back to regular steel ball/steel races? <br> <br>3. Why did you sand down the plastic washers - only because they became warped when you removed them or another reason? <br> <br>4. I don't have a rack foot (not even sure what that is), so I'd take your advice to use a socket to press in the bearing - any suggestion as to how to keep the socket centered? <br> <br>Thanks again.
A1. No, not a problem with 1mm more on the spindle. I didn't push extra 1mm because it's simply impossible. Bearings are pushed to the end basically.<br>A2. Hard to say if there's too much difference in performance. I'm not doing TT or stuff like that, that was simply an experiment. And at the end of a day, I still think I need legs rather than fancy equipment (and best area to shave weight is your body not a bike ;-)). What I can tell you is the whole drivetrain with approx equal push making exactly three spins of cranks (jokey wheels upgraded to TACX ceramic as well) in the same time new (~300km) Shimano 105 drivetrain is turning once. For the price I've paid for bearings I won't go back to standard bearings. Not only for the sake of performance but also because of durability.<br>A3. At first of all, plastic washers have a small bulge on the inside (I din't explain that, sorry). That is designed for 6mm bearings so you need to sand it down in order to push spindle trough. Secondly I sanded down slightly the flange to make the whole BB as close to original dimension as possible (probably gained about 1mm) I don't think it's necessary but you need to experiment.<br>A4. Rack foot is a standard foot for 19 inch rack systems ;-). Again my fault I didn't explained it too much. In order too keep socket cantered you need to centre the screw you're turning that's it. There is better/easier method where the required force is much lower. Simply put the bearings into freezer -25-30C for half an hour, and heat up cups with heat gun. Then you can literally push bearings with hands. You need to be quick thou ;-). <br>Hope that'll help. If you have any questions ping me a message/comment.<br>Keep'em rolling
Nice instructable. I have a set of FSA Mega Exo cups that need new bearings. I may give this a try on those and see if the result is the same rather than putting in a whole new set of cups. It surely would end up cheaper than having to replace the full set of cups my cross bike so often.
Great job! I took my Hollowtech cups to a bike shop to have the bearings removed, but the mechanic said he didn't have the tools to do it. <br> <br>I checked on the web and found out why. A press and the required adapter cost over $800! Which you functionally duplicated with a few shop scraps. I ended up getting new cups, but I like your solution better. <br> <br>The reason I had to change bearings is that my Boca ceramics self-destructed after only a few months use. The replacements have been going strong for 5 years. <br> <br>Q. What are you holding in your fingers in the first picture in Step 3?
Hi. Thanks for comment. On third picture is the &quot;puller&quot;. Two washers and between them another one cut in a half. But on that picture only one haf is shown. Hope that will explain a bit. Cheers
I like that: &quot;DO NOT DISASSEMBLE&quot;. Same as &quot;NO USER PARTS INSIDE&quot;. Just makes the project more interesting. <br> <br>Have you checked for bearings at Boca Bearings (www.bocabearings.com)? I get my small ball bearings here, they also have ceramic bearings. <br> <br>Good job.
Throw it, throw it, throw it, do not repair. <br>Buy, buy, buy, don't think too much. <br>Believe, believe, believe, don't ask.<br>Be consumer not human.<br>;-)
Woo! Good job, I came across this when doing a bit of research for my sheared rear axel. Nice post.

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