Wednesday, January 20, 2010

Crank Cull

Today, I present to you one of my least favorite bike components ever: The welded-together triple crankset.

I hate these for a couple of reasons: For one thing, they are heavy. For another, welding three chainrings permanently together prevents you from changing any individual chainring due to wear or personal preference. When one sprocket wears out, the whole assembly is effectively junk. The resulting junk is not easily recyclable in that it is mixed metal assembly, a hunk of steel-contaminated aluminum that is unwelcome at the scrap metal yard. I hate waste, and it bothers me that things are made to be so disposable, so I thought I'd see what I could do to repurpose and reuse one.

The subject of this experiment is a mid-90's Shimano Altus 38-32-24 from a Trek hybrid. It shows wear, but the 38-tooth sprocket still has some service life left. If only it could be freed from the albatrosses of its conjoined brethren, it would be a good fit for my current winter beater bike project.

I started by clamping the crank to a table. The fact that the pedal was still attached actually made it easier to secure it, so I'll pretend that I planned that. Next, I took a cutoff wheel to the 24-tooth sprocket, slicing it away close to its center.

I then tried to drill out the spot welds that held the 32-tooth sprocket to the biggest one, but didn't like how that was going. After accidentally drilling completely through the 38-tooth ring, I went back to the table and cut and ground it away with the cutoff wheel.

I ended up making five cuts and then breaking each fifth off with a big pair of pliers. An angle grinder would have been nice for the latter stages, but I didn't have one handy at the time. I made do with the cutoff wheel and cleaned up the sharp edges with a hand file.

I cleaned and sanded the remaining 38-tooth chainwheel, masked off the aluminum crank and primed and painted the freshly -exposed steel. I painted it blue because there was some blue Krylon handy. Whatever the color, a protective layer of paint was a must, given the corrosive salt bath it will endure on a cheap winter beater.

If I owned a drill press and had nice drill bits, I might have been tempted to drill a bunch of holes in it for some retro component-lightening flair, but I there is only so much time I'm willing to spend on this particular component. It's noticeably lighter as it is. This took about an hour from start to finish. I trial fit it to the bike, and it looks pretty good. Other than needing to swap the bottom bracket spindle for a narrower one (for a better chainline), I'm happy with the outcome of this experiment. The end result is that this part will be used again, which was the goal.


Erik Jorgensen said...

Cool, I've always wanted to try that kind of thing, The blue and orange look good together in a "meet the Mets" kind of way.

Billy Hoyle said...

That's handy 'Statement. Well done. Amazing what the paint did after all the hard work.

Darío Martín said...

Interesting, i have the same crankset in an old mtb which i'd like to convert to singlespeed. In some way i hoped the crank could be taken apart from the chainrings, so i'd better go for a cheap pair of cranks and a cheap chainring.

Have you experienced any kind of chain slipping?