Wednesday, May 05, 2010

Zen and the art of bicycle maintenance

We've been having the annual "Golden Week" holidays (just a set of public holidays that all occur sequentially) here in Japan, so on Monday we went on our traditional hilltop walk on the Ten'en Hiking Course around the north end of Kamakura to the famous Zen temple of Kenchoji.

Actually, this pic is an old one - on Monday it was crowded and we walked though fairly briskly. Outside of main holidays and fairly early in the morning it's usually more like this though. Chojuji was open, unusually, so we went in there too.

The centre of town was absolutely heaving so we quickly retired to our peaceful neighbourhood, and the bicycle maintenance job that has been hanging over me for a couple of months...replacing the rear bottom bracket on our tandem, which had developed an alarming degree of wobble.

Regular cyclists will probably know that the bottom bracket tends to be a particularly recalcitrant opponent and is prone to seizing in place. Sitting there at the low point of the frame where all the water and muck collects, it also has a large diameter thread and thus requires a high torque at the best of times. The rear of a tandem in particular has a large load applied with both riders' forces passing through it. With our tandem being aluminium, the threads in the shell are rather weak and prone to damage - plus effectively irrepairable, making it a potentially expensive job to attempt.

I read Zen and the Art of Motorcycle Maintenance fairly recently. Although nominally about motorcycles, it is also a pretty good bike maintenance manual (helped by the authors' habit of using the term "cycle"). The book's term "gumption trap" applies very well to the problem of a knackered bottom bracket - at least in my case. The cod philosophy is a bit annoying, though.

A few hefty blows with my trusty mallet had got one of the cups loose the day before, but didn't make much of an impression on the other side. I was left scratching my head - and thinking up strategies for finding and importing a new frame - when in a moment of inspiration I remembered the 6ft roof bar we had for mounting the tandem on a car roof (brought with us to Japan, but never used here).

Rather to my surprise, it worked, the threads on the shell are still at least somewhat intact (though a fair amount of powdered metal came out) and the new component is now installed. As the old saying almost says - if at first you don't succeed - get a bigger spanner!


Joe said...

Nice one. There is the mechanic's trick of putting the BB tool -- with bike attached -- into a vice and then turning the whole frame to loosen the cup. Worked for me with a stuck phil wood BB, though the cup did not survive the experience.

James Annan said...

Yes, a fixed vice would be nice. Not many places round here you can turn a tandem frame though! The back end was braced against a wall and jules was on the other end of the lever and also helping to hold the bike still.

Nosmo said...

Ammonia does a good job of freeing corroded aluminium. (Liquid wrench doesn't work). Some people recommend alternately heating and cooling.

I have used liquid nitrogen to help free a frozen Al stem in a steel frame, the coefficient of expansion of Al and steel is significantly different. But in your case if the shell is Al and the cups steel, then you would need heat not cold.

jules said...

So we should just have widdled down the tube - tsk - all that money we wasted on WD40!