Sunday, August 9, 2009

Bike Maintenance - Bottom Bracket Removal

Disclaimer: This article describes how I chose to do a particular task. It is presented as information, not recommendation - use your own discretion to decide whether my method suits you. If in doubt as to your capabilities, use your local bike shop.

My BB Removal kit - L-R: Crankbolt and washers, outside tap nut, Cyclo Bottom Bracket tool (shimano compatible).

The time had come to change the Truvativ square taper bottom bracket on my Giant SCR2.0. I had confidence that the bottom bracket (hereafter "bb") had been installed properly, as my bike was supplied by Rick Green's of Handforth, an excellent bike shop. (This is significant - poorly fitted bbs can "cold weld" into frames and become a large headache).

Before I started, I made sure I knew what thread my bb was. This is important, as "English" threaded bb cups loosen in different directions, depending which side of the bike you are working on. Not knowing the threading of your bb could mean you spending a day leaning on the spanner, getting nowhere and developing ever more inventive combinations of swear words to throw at your bicycle. As my bb shell on the Giant is English threaded, the tool must be rotated towards the front of the bike to loosen (clockwise on the drive side, anti clockwise on the non drive side). If this seems counter intuitive, it's because the tightening action thought to result from pedalling is the effect of the bearings on the bb cups, not on the cups directly. I think.

My first attempts were made using the tools from my Lidl bike tool set (a shimano splined BB tool with tall splines, that uses an 8mm allen key to turn it). The problem with this tool is that it has no way to hold itself into the splines on the BB. A properly fitted BB will be in the shell plenty tight, so without gorilla like grip, you'll struggle to hold the tool in place while applying the large amount of torque required to move the BB - at worst, you can damage the splines as the tool loses engagement. Pictured above is my bottom bracket removal kit, based on advice from my local bike shop, Manchester's excellent Bike Boutique. They suggest the use of a tool with shorter splines (measured vertically from top to bottom of the tool), a bolt the right size for the crank bolt hole in the bb spindle, and a large washer (usually sold in hardware stores as a "repair" washer).

My kit differs slightly, in that I used bits from around the garage - the bolt is the bolt from the square taper crankset that was originally on this bb, and instead of a repair washer I used the nut from an old outside tap kit (the washer and cap on the crank bolt are large enough to hold this securely).

The bolt and washer are used to hold the tool on to the bb cup, as pictured below;

End on view - the tool is held in place by the nut, which has been bolted through to the bb's spindle.

Another view showing the whole stack.

Remember that the purpose of the stack is to hold the tool in place so that it doesn't slip on the splines - it doesn't have to be hugely tight (you don't want to be working against it when turning your wrench). One advantage of the stack I used (as opposed to the repair washer) is that it doesn't overlap the wrench flats of the bb tool. I guess (although I didn't use one myself) this would make the use of a ring spanner or socket wrench possible. (On the cyclo tool, the wrench flats are 32mm in size, incidentally).

Once the tool is bolted in place, use a suitable spanner to turn the bb tool. On my bb, the drive side was movable using a headset wrench. Unfortunately, the non-drive side was far too tight for this to work, so I invested in a good quality 10" adjustable wrench to remove this side. Even here, a fair amount of force had to be applied to "break" the first turn- in my case applied with a rubber mallet to the end of the wrench - I'm not sure I'd recommend that approach to you, although I used "taps" of hopefully gradually increasing force.

As with lots of bike jobs, once I had the correct tools, and a bit of advice, the whole process was pretty straightforward. The Giant had its bb shell cleaned out, regreased heavily, and now sports a Hollowtech II bb and a Tiagra crankset. The old square taper crankset (with a lovely new FSA outer ring) will be used on my Long Haul Trucker build, once a replacement square taper bb arrives (the Truvativ one originally in the Giant is a bit gritty, so will not be reused).

1 comment:

Anonymous said...

Old post but no less brilliant with age.

Thank you.