The Golden Wrench

A blog about bicycle repair and maintenance by the mechanics at Freewheel Bike.

Saturday, February 27, 2010

Tough Love

Occasionally we have customers come into the shop with antiquarian rigs featuring seized or frozen components. Two dissimilar metals have been duking it out for decades, and eventually they just can't let go of one another. Kind of like the two male mooses who got their antlers stuck together fighting over a particularly virtuous she-moose, or the plot of Romeo and Juliet. Yes, sometimes these conflicts end up messy, and we are called on to mediate.

Our job is to break the wills of taciturn components. And we have turned it into a nuanced art.

This particular customer came in with a very fetching purple Maruishi singled road bike. Japanese steel: very savory! Unfortunately, the seat post was chemical welded into the frame. It's like a chemical snowball fight between an Irishman and a pacifist. The aluminum says "Ya flanny gaet, aeet some SNUUUUUU" and the steel says "Fine, I'll go ahead and keep them" and an electrolyte (salt from toxic sweat or from the road) begins egging on the Irishman from the sidelines. Soon, electrons are zinging across from the aluminum to the steel at a great rate, causing the once-smooth surfaces of both metals to become rough and scratchy. The battle can cause quite a mess, and breaking them up is hard to do.

A couple of themes are involved in a seatpost extraction. The first is leverage. The seatpost stuck in the frame is often made out of aluminum just slightly firmer than mashed potatoes, and therefore putting leverage on it is a delicate proposition. Too much leverage improperly applied tends to smoosh and shred and squarsh the seatpost without actually breaking the bond. Not enough leverage makes the seatpost giggle, and that's just demoralizing. Here is a brief pictorial tour of the clever setup that our chief persuader devised for the task at hand.

Man does not live by torque alone, however. Another aspect, lubrication, plays a crucial role in the operation. Lubrication puts little ball-bearing shaped molecules of oil between the bonded surfaces, making the seatpost and frame lose some interest in the dispute. We leave a penetrating and corrosion-attacking substance in the frame overnight to do its insidious work before reapplying leverage. If this doesn't work (which it didn't in this case), we get out the final step: flame.

MAPP gas torches are not just for heating tepid coffee (just visible in the lower right corner of the picture). They are a powerful tool for unlocking seized components. One might object that aluminum (seatpost) expands faster than steel (frame), so wouldn't that make the situation worse? I would answer "SILENCE!!!" because somehow it just works. The different expansion rates sometimes cause the little aluminum oxide teeth to shift from their little rust detents just enough so that one can wrangle it out. Sometimes it works, other times it just stinks up the neighborhood for a few hours and cooks a frame. Like Romeo and Juliet.

In the present case, the snowball fight ended up with two casualties. The Maruishi gave up the ghost but not the post.