I've read several forum posts comparing a wide variety of expensive and well made bottom brackets for cranksets with 24mm spindles. The best bottom bracket is most likely the existing one you have. Unless you're sponsored by someone giving you premium bottom brackets for free, or you have absolutely no mechanical ability, don't waste your money on a premium brand bottom bracket. My little LLC stays wide open improving bearings for bottom brackets and hubs. I'm so busy with the work, I'll never reach everyone so they can get the most potential out of their existing equipment. First off, nearly all bottom brackets for 24mm spindles use a bearing with a 25mm inner diameter. The manufacturers do this so they can anchor the plastic shield over the bearings by using the plastic sleeve that slides inside the bottom bracket bearing. You'll never reach your maximum potential with your spindle and bearing separated by the plastic sleeve that holds the dust cap in place. To make your own high performance bottom bracket, follow these steps and amaze yourself and friends.
Step one- remove you're cranks and pry out the plastic dust cap off of each side of your bottom bracket.
Step two- remove bottom bracket, remove the spindle tube and reinstall just the bottom bracket cups with the bearings still in them.
Step three- use a blind hole bearing puller, if you have one, to remove the 25mm bearings. If you don't have a blind hole puller, use a long screwdriver to drive each bearing out from the opposite side. Don't worry about damaging the bearings because they belong in the trash can.
Step four- buy two bearings that have a 24mm ID, a 37mm OD and a 7mm width. I have my best results with the inexpensive Enduro MR 2437 LLB C3. This is an ABEC 3 stainless steel bearing with blue seals.
Step five- remove the seals from both bearings using a dental type instrument from a $3 pack of 5 available at hobby lobby. Next, wipe any residual blue grease from the interior of the seals. Be careful so you don't bend them. You can lay them out, interior side up, and clean them with a Q Tip.
Step six- using your choice of solvents remove all the remaining grease from inside the bearing. Isopropyl alcohol works well, if you have a container that seals and allows you to shake it vigorously. If you're in a big hurry, spray them with aerosol brake cleaner. Collect the brake cleaner as you spray them in a sealable container. Once they are visibly clean, seal them in the container with the collected brake cleaner and shake them for 3-5 minutes.
Step seven- apply a light coating of Tungsten Disulfide (WS2) to the interior of the bearing using a small model kit paint brush. If you need an inexpensive source for WS2 powder you can order "Derby Dust" online. The 2 ounce container is inexpensive and will last you the rest of your life. This may seem like a hassle, but after you witness the end result, you'll be doing this to every bearing on your bike.
Step eight- once all the balls and races are coated with WS2, replace the previously cleaned seals after tapping out any excess dry film lubricant (WS2). While holding the bearing spin the interior race and exterior race both directions, frequently rotating the bearing, with a dremel tool on the lowest setting. At this point you are "running in" the treated bearing. If the bearing locks up due to excess WS2, add 1-2 drops of really light oil. I prefer Royal Purple ATF but mineral oil works fine. After a few minutes the bearing will break loose on it's own and you can run it in using a dremel. I usually go 5 minutes in each direction on the interior and exterior race. Once this step is complete, when you flick the bearing with your finger, expect 20-30 revolutions.
Step nine- press your new bearings back into your cups. I use a field press, which is essentially a piece of allthread with two handles and dies. I have used a dead blow plastic hammer or even the end of a 2x4 with a normal hammer.
Step ten- using a coping saw, dremel or sharp knife, cut the portion of the bottom bracket dust seal off that used to slide into the old 25mm bearings. Re-install all the pieces of your bottom bracket and coat the edges of the cup with a very light layer of RTV or silicon to hold the bottom bracket dust seals in place.
Step eleven- reinstall your cranks and see what if feels like to actually have your spindle in contact with your bearings. I know you've seen the "spin test" videos on the internet. Do your own and smile as you watch your cranks spin until you physically stop them.
The whole lesson is: No matter how much you pay or how highly touted a particular bearing may be, no bearing ever performs to it's full potential when it's separated from the spindle by 1/2 a mm of junk plastic bushing. Also, no bearing can reach it's full potential when it's packed full of highly viscous grease. Google WS2 and you'll instantly realize that dry film lubricants, especially WS2, are far superior to any liquid lubricant or ceramic. You've made a bottom bracket that performs better than ANYTHING you can buy. As long as the cups thread in properly and the bearing cups are true, go as cheap as possible. I prefer the ROTOR BB1. It's ROTOR's bottom of the line bottom bracket but I've yet to encounter one that's not machined perfectly. I believe they only come in black. If you absolutely want it to match Shimano cranks, spray the bearing cups with Easy Off oven cleaner. After a quick scrub, you'll be left with raw aluminum cups. They look nice raw but you can always polish them right up with your dremel and some Mother's paste. After you've completed this project, go ahead and do your hub and driver bearings. In my opinion it's well worth the little bit of money to get Enduro ABEC 3 stainless bearings. I've tried just about every bearing out there and they seem to perform the best. Sometimes it's hard to make yourself pull expensive ceramics or high ABEC rated Swiss bearings. If you need the motivation, spin your cranks again. It's worth it! For maintenance, since WS2 is resistant to every solvent I tried, pop the seals off the bearings once a year or two and simply douche the interior of each bearing, in place if you can reach it, with a syringe full of 90+% Isopropyl Alcohol. Then ride to warm them up. After a few good rides, your balls and races are the prettiest deep cobalt blue. Once you've seen this, you've got a happy bearing that will give you years of great service and typically continue to only get better. How do you know when to replace them? After several years, depending on what type of riding you do, you may feel a slight "tick" when a side load is applied to the cranks or hubs. This lets you know to go ahead and order your replacement bearings, hunt down your WS2, buy your can of brake cleaner and warm up your dremel. You should get a minimum of 4-5 years. If you do happen to submerge your bearings all you need to do is break out the hair dryer. Simply pull the seals and rotate the bearing as you blow hot air on them.
Step one- remove you're cranks and pry out the plastic dust cap off of each side of your bottom bracket.
Step two- remove bottom bracket, remove the spindle tube and reinstall just the bottom bracket cups with the bearings still in them.
Step three- use a blind hole bearing puller, if you have one, to remove the 25mm bearings. If you don't have a blind hole puller, use a long screwdriver to drive each bearing out from the opposite side. Don't worry about damaging the bearings because they belong in the trash can.
Step four- buy two bearings that have a 24mm ID, a 37mm OD and a 7mm width. I have my best results with the inexpensive Enduro MR 2437 LLB C3. This is an ABEC 3 stainless steel bearing with blue seals.
Step five- remove the seals from both bearings using a dental type instrument from a $3 pack of 5 available at hobby lobby. Next, wipe any residual blue grease from the interior of the seals. Be careful so you don't bend them. You can lay them out, interior side up, and clean them with a Q Tip.
Step six- using your choice of solvents remove all the remaining grease from inside the bearing. Isopropyl alcohol works well, if you have a container that seals and allows you to shake it vigorously. If you're in a big hurry, spray them with aerosol brake cleaner. Collect the brake cleaner as you spray them in a sealable container. Once they are visibly clean, seal them in the container with the collected brake cleaner and shake them for 3-5 minutes.
Step seven- apply a light coating of Tungsten Disulfide (WS2) to the interior of the bearing using a small model kit paint brush. If you need an inexpensive source for WS2 powder you can order "Derby Dust" online. The 2 ounce container is inexpensive and will last you the rest of your life. This may seem like a hassle, but after you witness the end result, you'll be doing this to every bearing on your bike.
Step eight- once all the balls and races are coated with WS2, replace the previously cleaned seals after tapping out any excess dry film lubricant (WS2). While holding the bearing spin the interior race and exterior race both directions, frequently rotating the bearing, with a dremel tool on the lowest setting. At this point you are "running in" the treated bearing. If the bearing locks up due to excess WS2, add 1-2 drops of really light oil. I prefer Royal Purple ATF but mineral oil works fine. After a few minutes the bearing will break loose on it's own and you can run it in using a dremel. I usually go 5 minutes in each direction on the interior and exterior race. Once this step is complete, when you flick the bearing with your finger, expect 20-30 revolutions.
Step nine- press your new bearings back into your cups. I use a field press, which is essentially a piece of allthread with two handles and dies. I have used a dead blow plastic hammer or even the end of a 2x4 with a normal hammer.
Step ten- using a coping saw, dremel or sharp knife, cut the portion of the bottom bracket dust seal off that used to slide into the old 25mm bearings. Re-install all the pieces of your bottom bracket and coat the edges of the cup with a very light layer of RTV or silicon to hold the bottom bracket dust seals in place.
Step eleven- reinstall your cranks and see what if feels like to actually have your spindle in contact with your bearings. I know you've seen the "spin test" videos on the internet. Do your own and smile as you watch your cranks spin until you physically stop them.
The whole lesson is: No matter how much you pay or how highly touted a particular bearing may be, no bearing ever performs to it's full potential when it's separated from the spindle by 1/2 a mm of junk plastic bushing. Also, no bearing can reach it's full potential when it's packed full of highly viscous grease. Google WS2 and you'll instantly realize that dry film lubricants, especially WS2, are far superior to any liquid lubricant or ceramic. You've made a bottom bracket that performs better than ANYTHING you can buy. As long as the cups thread in properly and the bearing cups are true, go as cheap as possible. I prefer the ROTOR BB1. It's ROTOR's bottom of the line bottom bracket but I've yet to encounter one that's not machined perfectly. I believe they only come in black. If you absolutely want it to match Shimano cranks, spray the bearing cups with Easy Off oven cleaner. After a quick scrub, you'll be left with raw aluminum cups. They look nice raw but you can always polish them right up with your dremel and some Mother's paste. After you've completed this project, go ahead and do your hub and driver bearings. In my opinion it's well worth the little bit of money to get Enduro ABEC 3 stainless bearings. I've tried just about every bearing out there and they seem to perform the best. Sometimes it's hard to make yourself pull expensive ceramics or high ABEC rated Swiss bearings. If you need the motivation, spin your cranks again. It's worth it! For maintenance, since WS2 is resistant to every solvent I tried, pop the seals off the bearings once a year or two and simply douche the interior of each bearing, in place if you can reach it, with a syringe full of 90+% Isopropyl Alcohol. Then ride to warm them up. After a few good rides, your balls and races are the prettiest deep cobalt blue. Once you've seen this, you've got a happy bearing that will give you years of great service and typically continue to only get better. How do you know when to replace them? After several years, depending on what type of riding you do, you may feel a slight "tick" when a side load is applied to the cranks or hubs. This lets you know to go ahead and order your replacement bearings, hunt down your WS2, buy your can of brake cleaner and warm up your dremel. You should get a minimum of 4-5 years. If you do happen to submerge your bearings all you need to do is break out the hair dryer. Simply pull the seals and rotate the bearing as you blow hot air on them.