Written by Oz on Wednesday, 24 Mar 2010.
What is an External Bottom Bracket and Crankset you ask.......
The external BB is latest link in the evolution of threaded bottom brackets.....and the cranks are also pretty nifty too. Similar to the now legendary Bullseye BMX crank, modern cranks sets rely on an integrated arm/spindle with the other arm being removable. By making the spindle separate from the bearings, the bearings could then be made larger and placed outside of the bottom bracket shell; hence the name external bottom bracket. The spindles are also made hollow and significantly larger in diameter. This design has drastically widened the stance of the bearing/spindle interface resulting in near flex free performance all while reducing the overall weight of the crank and BB. This system is employed on nearly every road and MTB bike over $700 made today and will eventually trickle down into the entry level bikes just like threadless headsets and disc brakes. This system has also simplified the installation of MTB and road cranksets and made life alot easier. One thing that is nice about external BBs is that there is really no need to hunt down a specific size (spindle length, shell width)....everything you need is packaged together and for the most part, they are fairly cheap. There is no more guessing spindle length (unless you have some one-off DH rig) because the spindle is part of the arms. Shell size got you guessing? No worry....spacers are included for 68mm, 73mm and e-type installs.
Much like any other part that goes on a bike, the installation is pretty straightforward; but there are a couple things to take note of and pay special attention to. Follow this basic tutorial and even the most mechanically challenged should be able to knock this out in under a 1/2 hour.
Tools that you will need:
- Repair stand....although this could be done old skool BMX style with the bike flipped upside down on the bars.
- External BB tools (Shimano, Park, Pedros, etc).
- Allen Keys....5mm, maybe a 6 & 8 depending on cranks...
- Rubber mallet (optional)
- Anti-seize.......an absolute must for East Coast BB installs.
Parts that you will need:
External bottom bracket and a set of cranks to match....
Note: possible thread chasers or taps if your BB shell is munged up. These are hella expensive and sometimes tricky to use so you might wanna leave this procedure to a shop if it needs to be done.
Remove cranks and old BB. Remember that drive side loosens clockwise and the non-drive loosens counter clockwise. Clean up the shell area and inspect for damaged threads. If the threads are munched, say a prayer and then bring it to a shop and hope for the best.
Prep the inside of the BB shell with a light coat of anti-sieze or grease. You will thank me later when you eventually need to remove your BB. I use anti-sieze exclusively and so should you. Messy stuff, but worth every penny.
Measure your shell width. It is either 68mm or 73mm. Cross reference that shell size with the chart that was hopefully included in your BB. Generally......68mm shells will use 2 spacers, e-type derailluer set ups will use one and 73mm will use none. My bike has a 68mm, but TruVativ arms can be snugged up tight on a narrower BB (.....my bike should have 2 spacers). Why would i do this? Narrower chain line, better shifting and longer drivetrain wear. However, this setup may not be possible with all cranks/BB so you better do what the instructions say and leave the fanagling to the experts.
If you didn't put anti-seize on the BB threads, put it on the cup threads. Then find your drive side cup and press the plastic sleeve into the backside of the cup. This keeps the creepy crawlys out of your bearings so you better do it.
Install the appropriate spacers for your shell width and slide that drive side cup/sleeve combo into place (on the drive side duh!) and gently start threading it in a counter clockwise direction. If it starts to get tight right of the rip, stop and make sure it is not cross threading. If your threads are good it should spin on fairly easy.....keep threading until it bottoms out. Now get that BB tool and torque that cup down good and tight. These cups dont have a lot of meat so make sure that tool is on correctly or it will be bloody knuckle time.
Grab the other cup and appropriate spacers and do the same procedure, except that this side threads opposite and tightens in the clockwise direction. Make that cup snug as a bug.
Put a light coat of grease on the spindle and slide the drive side arm/spindle into place. I think some Raceface cranks do the opposite arm and spindle together, but you'll figure that out. Lighly tap the arm with your hand or a rubber mallet and make sure it is seated. Before you go any further, now is a good time to make sure that the arms and rings don't hit the frame.
Line up the arms and slide the non drive arm into place. If you have a Shimano system, install the outer cap and use the proper torx style tool and tigten it with only hand pressure. If you try to snug this down old school style you will bind everything up and possible damage the bearings. Hand tight is all you need. Check the spin of the cranks (some slight resistance is okay, don't expect them to spin like a wheel)......and then snug down the fixing bolts with a little force. Once they are both finger tight, torque them down a 1/4 turn each back and forth til they are snugged good. Do not tighten one all the way then do the other. This might cause the second bolt to bind and potentially lead to a loose arm.
If you have a set up like mine, line up the splines and then start tightening the fixing bolt into the spindle. Make sure it goes on all the way and snug it up per manufacturer's specs. Again, check the spin and clearance and rock the arms side to side to see if there is any play. If the arms hit, you probably need the spacers.
Install your pedals and chain and check to see if the front derailluer needs an adjustment on the high/low stops and you are good to go.
Put some miles on the bike and check the arms every now and then for the correct torque. Other than that, avoid power washing your BB and limit your submerged river crossings to less than once a year and your new BB should give you plenty of life. If your cranks creak down the road, check the chainring bolts and arm first, then snug the cups, then check for lube on the cups and/or spindle.
Now a word about facing:
No, i am not talking about the social networking phenomenon Facebook, but rather the age old practice of ensuring your BB cups sit tight and right. I am sure someone out there is gonna question why i did not reference facing the BB shell during this tutorial.
What is facing? In layman's terms, it is the process of using a tool with a set of cutters that is installed into your BB and turned in order to machine the BB shell faces parallel with each other. A lot of old lugged chro-mo bikes back in the day required this but times have changed. Here are some reasons why I don't face anymore.
Reason 1 - Facing tools are expensive, i know a lot of shops that don't even have a set of BB taps in stock let alone a Hozan or Park facing tool. This stuff is pretty uncommon nowadays. I have done this practice in the past, but haven't done it to a frame in over 8 years.
Reason 2 - Facing guarantees a parallel BB shell, but most of the quality frames built today are faced and chased at the factory and you would be hard pressed to find that they are off by more than a couple of thousandths. Back in the 80's and early 90's a lot of the imported frames from Europe needed to be faced on the head tube and BB.....thankfully the Chinese have done this for us.
Reason 3 - Unless your BB is ridiculously out of wack, the bearings should be fine. Your BB stands a better chance of enduring a premature death from outright neglect and abuse than it does from sitting a thousandth or two cockeyed. Trust me, smacking your crank arms into rocks 20 times a ride and power washing the grease out of your bearings after a mud ride is way worse than a non-faced BB any day.
If you have any questions or want to follow more discussion regarding this article, please visit it's original forum post.