Folding Bikes Blog

Montague Overhaul IV: BB and Cranks

I’m right in the middle of rebuilding a Montague Boston as a fixed gear commuter. With all standard components, Montague bikes are really the only folding bikes out there that can be fully customized with any parts you want. I’ve stripped the frame down to the bare essentials,  cleaned and regreased the headset, and prepared my new wheelset. Now I’m going to install the new bottom bracket and crankset.

I have a Shimano, square taper bottom bracket ready to go:

Most modern BBs use sealed cartridge bearings, so you won’t have any loose bearings to deal with. The sealed cartridge design is certainly easier to deal with, and keeps everything better protected from the elements. The drawback is that it doesn’t allow you to access the actual bearings to clean and regrease them. If they do start to go, you need to replace the cartridge.

The first thing to consider when choosing a bottom bracket and crankset, is what type your frame is made for. All Montague bikes, and a large number of bikes on the market now, use a 68mm, English threaded BB. 68mm is the width of the bottom bracket shell, and “English threaded” describes the size and spacing of the threads. Other frames (generally older, European frames) may have French, or Italian threads with a wider 70mm shell. Many new, high end road and mountain bikes are now using press fit bottom bracket cups that do not use threads at all. The spindle is then integrated with the crankset. The design provides weight savings, and apparently, increased stiffness.

Anyway, back to the task at hand. On this BB, the drive side cup is fixed, and the non-drive cup is separate. Make sure the threads in your frame are clean, and apply grease (or lock tight, or teflon tape). There are conflicting opinions on which is best, but I prefer good ol’ fashioned grease:

 

You should remember from removing the old BB, that the drive side is reverse threaded. You will need to turn the cup counter-clockwise to tighten it. Start by turning it in by hand to ensure it doesn’t cross thread. When necesary, switch to your splined BB tool. There are different tools for different bottom bracket designs, so make sure have the correct one:

You should use a torque wrench to tighten it with the torque specified by the BB manufacturer. In this case, it’s 50-70 N/m. Once that side is tight, grease the non-drive side cup, and start threading it in as well. This side uses standard threading, so clockwise will tighten it. Again, use the manufacturer’s specified torque:

Wipe off the excess grease, and you’re ready for a new crankset:

For this build, I have a set of All-City track cranks. They’re a solid, very durable  single speed crankset, and although I went with black, they do come in a variety of colors:

With a square taper bb interface, crank installation is pretty simple. Just slide the crank arm on to the spindle:

Whether or not to grease the spindle is another one you’ll hear varying opinions about. Some say grease will actually allow you to over tighten the crank arm, making it very difficult to remove later. I went for the dry installation. With the crank arm in place, simply thread the crank bolt into the spindle, and tighten it down (again check what the manufacturer suggests for torque):

Install the other side in the same way, making sure the cranks are 180 degrees opposite of each other. The square taper spindle is symmetrical, so it is possible to rotate either crank arm by 90 degrees, but I guarantee you’ll find it difficult to ride that way. Next we’ll install the track cog on the rear wheel, mount them on the bike, and finish off the drive train with a nice new chain.

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3 Comments

  1. Suncoast
    Posted December 27, 2012 at 10:24 am | Permalink

    Thank you for this helpful guide to building a Montague bike! Looks like a lot of hard work does pay off!

  2. Andrew6Ger
    Posted April 21, 2013 at 5:27 am | Permalink

    Thankyou for showing me how easy it was to replace the BB. I’ve just replaced mine with a the BB-UN55 also.
    Looking forward to smoother running on my way through hyde park tomorrow.

  3. Posted May 2, 2013 at 7:20 am | Permalink

    Excellent Andrew! Getting your hands dirty working on your bike, is half the fun of owning it (in my opinion!)

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