Professional Repair and
Shop Operation Class

Wednesday, December 7, 2005

Suspension Forks and Frames

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One of my goals for the class was to learn more about suspension forks. There must be hundreds of different suspension forks in use today, so many that UBI holds a three-day workshop on repair and maintenance of suspension forks. Evans gave a good overview of the topic. The hands-on exercise involved changing the oil in a Manitou fork.

Suspension forks are complex objects. (First Flight Bikes Web site contains a brief history of the suspension fork.) They must be able to absorb the impact
Disassembled fork
of the front wheel as it contacts rocks, roots and other obstacles encountered during a downhill ride. Once the impact has been absorbed, the fork must then return to it's previous position to repeat the process and keep the wheel in contact with the ground. With a fluid, oil-based suspension, the flow of oil is used to control movement of the fork. Various spring mechanisms are also used to absorb road shock. Oil is forced through an opening that is adjusted for more or less flow, allowing more or less movement of the fork. Upon recoil the oil flow determines how quickly the fork returns to it's previous position.

We disassembled a suspension fork, removed the existing oil, and replaced it with new oil.
Anna
In our case we used the original oil, as the bike had never been ridden. It was an instructive process, but we just barely touched on the topic.

In the afternoon Anna gave us an overview of bicycle frame materials. She also discussed the various welding techniques used to assemble the frames from tubes. Later we used expensive, specialized tools to modify the bottom bracket and head tube to ensure that the two ends were parallel.
Facing the head tube
The two ends must be parallel so that the bearing cups are parallel and provide parallel surfaces for the bearings to rotate evenly. The process of shaving the metal on the tube ends is called facing.

After class I rode to Señor Sam's for an excellent vegetarian tostada. The place is located away from the downtown area, near the university. As I was studying the workbook while eating, John of UBI stopped by the table to say hi. Later I rode to the university library to check email and to catch up on my online reading. Back at the hostel I studied a bit more and talked to the others who were busy finishing a bottle of rum.

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