Bike Repairs – new bottom bracket


English: WD-40
English: WD-40 (Photo credit: Wikipedia)

I used to repair and upgrade my old road bike regularly, taking it from a 12-speed to 21-speed in the process.  The only things I haven’t replaced on that old thing are the front rim and hub, brake callipers and the frame.

My newer bikes are a different prospect.  Firstly, my big old tools aren’t needed or just don’t fit.  My Cannondale Super V is weird anyway and my Trek Domane can be taken apart using only Allen keys.

The Cannondale has been clicking on the bottom of the pedal stroke for a while.  At the last service I was assured that the BB was fine, whereas the rear hub bearings were stuffed.  I wasn’t so sure.

Luckily, I only needed a new BB tool, Park Tool BBT-32 as my old crank puller would do the rest.  I also bought new Park Tool PPL-1 PolyLube from Bike Culture.

Crank bolts were removed with 8mm Allen key, then the cranks were pulled.  I used the BBT-32 on the non-drive side to remove the plastic cup.  Removing this side first releases pressure on the drive-side thread and will make removal a little easier.  The hardest part is keeping the splines of the tool engaged; clean the cups with a brush beforehand.  Even then, the tendency was for the tool to twist out.  The thread is quite stiff until the cup is all the way out.

The drive side wasn’t budging.  I sprayed WD-40 from the other side to penetrate the thread and a few minutes later the BB was free.  The threads are integrated into the body of the BB.

A few turns of the axle and the grinding was obvious.  It is not unusual to have some resistance when you turn the axle, but this was gritty and sticky and yucky.  And not a user-serviceable item, either.  While everything was off the bike I removed the chain-wheels and gave everything a good scrub in the parts washer.  The black cranks and chain-wheels polished up nice.

As luck would have it, Pushys Wheels were having a Boxing Day sale, so there was hope of getting a new BB.  I needed a 68mm (width of the frame at the bottom bracket) x 111mm (width of the axle) but had to settle for a 68 x 113.  The extra 2mm would require a change of chain-line at the front, which shouldn’t be too much to compensate for, I thought.

Fitting was straightforward, using plenty of lube on the threads and a very thin layer on the cranks tapers.  (Old timers might shudder at the idea if greasing the tapers before replacing the cranks, but a thin layer will help to seat the crank and won’t make the cranks round out.)  Once it was all back together, I rode around for a bit and re-tightened.

The front dérailleur needed adjustment.  The front mech has always been temperamental; last weekend it threw the chain off the small ring and the large ring on one ride.  I shifted the limit screws to some semblance of 2mm and put some tension in the cable adjusters.  I had enough to get into all front chainwheels, though the middle needs a little more thumb than usual.  I really wanted a ride by the afternoon, so fine adjustment could wait.

During the ride (more on that later), I adjusted the shifting a little, but it is still hit and miss.  Fortunately the rear shifts as sweetly as ever, so I could stick to a chain-wheel and grind one out.

Or rather, not grind.  The smooth action from the new BB was immediately obvious.  I often put a lot of expectation on any adjustment or new component to have benefits several orders of magnitude greater than their cost.  But I could tell that even steep and loose hills were easier to climb and the pedal action was much smoother.  Not bad for $40 (+$40 for tools and lube).

Bicycle repair can be liberating and cheap; not only saving on labour costs but also by extending the life of existing components and knowing when to replace before failure in an inconvenient location.  Proper tools are essential to avoid expensive injury to bike and self.  And a workstand helps (Pushy’s have a nice one reduced to $99.)  And it keeps your mechanic honest.

 

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