How Tight Should a New External Bottom Bracket Be?
 

My newly-installed 105 external bottom bracket is tight enough that the crank only spins 1.5 turns when I flick the pedals. (With no chain.) I’m wondering if new ones are normally that tight.

The story:
I installed a new 105 external bottom bracket on my (CF) Roubaix tonight. I noticed right out of the package that the bearings seemed stiff, taking a slight force to spin them. I was hopeful this might mean they were actually full of grease. The problem came when it was time to insert the drive-side crank’s axle through the bracket. It went in less than an inch and then took some palm pounds to get it in most of the way. And then it just stopped. I actually had to use the wooden handle of a hammer to “pound” it in the rest of the way. All the while I was concerned about the lateral pressure on the bearings – usually not a good thing.

Even when the crank was barely in (before the force) it was not particularly free-spinning. At least it didn’t worsen after the force fit. So now it “spins”, but only makes 1.5 turns when I flick it from the pedal. So, while I doubt I made it worse, I’m wondering if the tightness it exhibits is normal for a new external bottom bracket. I had not had the crank off the previous one until it had 17K miles on it. At that point it spun just fine. :D I’m just looking for some other experiences on how freely-spinning a new one is supposed to be. And how hard it should be to get the sucker all the way in. :(

Totally normal. Virtually all external BB's are that tight.

sounds like business as usual. enjoy

Did you apply a small amount of grease to the axle (actually spread a very thin layer over most if not all of axle before trying to pound it thru the BB cups?) The bearings will seem tight but crank should feel very smooth as it spins.

^ Yep; greased everything. The result is a solid feeling BB; NO lateral play at all. VERY smooth spinning, but not effortless spinning. So far the replies say all is normal. But I'm still curious how much force is typically used when "inserting" the crank in. I had to literally pound mine in the last 3/4-inch or so.

The part about how you installed your BB scares me. Everything, I mean EVERYTHING I've read, and from my own tooling experience, if any kind of excessive force is required to install the BB, its crossthreaded. It should screw in by hand until the very end where you need to torque it.

Did you use grease or antiseize when you installed it? Did you clean the threads in the BB shell after removed your old BB?

^^ Installing the BB was a piece of cake. No force required. It's not cross-threaded. I'm talking about inserting the crank after the BB is in place - getting the crank "axle" through the BB.

Oh ok, sorry....I mis-read the part about the hammer lol.

My hollowtech II is the same way. It's not as freely spinning as my square taper stuff, but works perfectly. I doubt the "tightness" of the bearings makes any difference in resistance felt when riding. Just make sure that if yours has the little preload cap that you spin the cranks each time you hand-tighten that cap and back it off if the cap creates a noticeable side-load on the bearings.

I have a similar concern, but in reverse. The shop installed a 105 external BB then pounded in with a MALLET an FSA Gossamer crank. Now I can't easily get the crank out, but I haven't resorted to any significant force yet.

Previously the bike had a Mega Exo BB through which the crank slid in and out without any force required. I currently have another bike with Mega Exo and FSA crank that also pulls out easily.

So... is Shimano and FSA really compatible? I'm planning on replacing the 105 with an FSA BB because of a year of all weather riding, and because I'm rebuilding the bike as my wife's 1st road bike (figure I should replace the really worn parts).

brian

yeah, it's fine. sometimes it slides right in, no problem... sometimes I have to take the rubber mallet to the driveside crank to seat it all the way in. ymmv, but it's very hard to mess this up...

Mine required a little tap with a rubber mallet as well, but nothing too forceful.

My general approach to installing the actual bb (since I don't have my own torque wrench) is to basically slip the bike over and tighten the cups just about as tightly as I possibly can with the tool. Works great - never had an issue.

Exactly my situation: FSA Gossamer crank and I'm using the 105 BB this time. And same experience - had to pound the crank in. FSA assures us it's compatible. So now I wonder if a 105 crank sometimes has to be pounded into a new 105 BB. And in your case, it sounds like it may need to be pounded back out.

Mine IS going to need pounding out. The shop had to pound it in quite a bit. Doesn't sound right to me, in many years working on bikes. Especially if a same brand combination doesn't require any force.

I think that the 105 is better quality, but I'm going to carry on with what feels like a better fit.

Good luck!

Brian

Oh and regarding your original question, the crank currently spins better than when it was first installed, after a thousand K or so.

Well I don't know much (could just stop there) about carbon I do know that if the BB faces are not square it will cause problems like these.

+1. Find a shop that will face the bb shell. It may make the whole thing easier to assemble and give much much less friction because the bearing alignment will be better. Also, misaligned bearings will wear out much faster than properly aligned ones.

I doubt anyone's got the equipment or the cajones to try to face a CF BB at home. In fact Specialized's Tech Docs explicitly tell you not to. Moreover the Gossamer crank fit fine in the Mega-Exo BB so I doubt the BB faces were the problem. Since 2 of us here are reporting the same problem, probably on different frame modes, I think a safer bet is that the FSA crank and BB are just a skosh bigger than the 105, despite FSA's claim of compatibility.

I got 33K miles out of my Mega-Exo BB, and would have replaced it with another one, but I read so many BF posts ragging on it, that I switched to the 105. Not to mention that the street price of the 105 is half that of the Mega-Exo. Base on this fit, though, I may go back with FSA. On the bright side, the crank is rock solid, absolutely no play, and rode great tonight. I only hope the pounding didn't shorten the BB's life. We'll see.

Bring your bike over tonight. I'll do it in my basement, but let me finish my usual Friday night case of beer first.