Speedking Fork Lowering

Article By: Will Ramsey – Faith Forgotten Choppers

Originally Published In The July 2013 Issue Of Cycle Source Magazine

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This month, I decided to change things up and venture out of my shop in search of new tech article information. I found myself in Cincinnati, Ohio at Jeff Cochran’s shop, Speed King. I’m quite sure Jeff needs no introduction. This guy has built more motorcycles than most have dreamed of. His builds have simple clean lines and embody a minimalist “form follows function” approach to design. In order to obtain the well-known Speed King look, Jeff pays close attention to every detail involved in his builds. His bikes maintain a consistent and balanced stance and his understanding of proper engineering ensures that a Speed King bike will always perform extremely well. In this tech article, Jeff walks us through his process of shortening a hydraulic frontend in order to achieve that perfect stance while maintaining excellent performance for the next Speed King bike.

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Jeff lays out the simple disassembly/assembly tools needed to perform this operation: an impact driver,? a socket for the fork tube cap,? a long 6mm Allen? and a scrap piece of ¾ schedule 40 PVC.

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Using the impact helps ensure that the fork tube does not try to rotate in the vise as the fork tube cap is unscrewed.

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Jeff warns that the preload on the spring can transform the fork tube cap into a dangerous projectile.

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Now, Jeff measures the factory preload on the fork spring and records it (3/4”), ensuring that he can return the springs to their proper length. This preload can vary depending on the manufacturer so be sure to measure.

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Jeff completes the disassembly of the fork legs.

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In order to shorten the fork legs, the rebound spring must be spaced down on the damper tube.

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Jeff has determined that he needs to shorten this particular set of legs 7/8” in order to achieve the correct stance. Therefore, he simply cuts two 7/8” spacers from the PVC and slides them on the damper tube above the rebound spring.

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Now with the spacer installed, the spring preload is far too long. The factory preload measured earlier is marked so that the fork springs can be cut to the proper length.

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It is wise to mark both springs and check to see that they are identical in length before cutting.

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Symmetrical cuts are made on both fork springs using a cut off wheel.

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Jeff uses a disk grinder to sand flats on the top of both springs.

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The fork tube is placed back in the vise and secured with a scrap piece of carpet to keep the vise jaws from scratching the chrome.

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Using the impact, Jeff compresses the fork spring and tightens the fork tube cap. He is very careful not to cross thread the cap before pulling the trigger on the impact!

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With the rebound sleeve in place, Jeff measures the total possible travel of the fork before bottoming out. This is a critical measurement and must be checked against the distance between the lower leg and the bottom fork tree.

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The lower leg is slid back over the fork tube. Make sure that the rebound sleeve registers in the bore at the bottom of the lower leg.

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Using the 6mm Allen, install the fork screw with the brass washer at the bottom of the fork leg.

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Jeff stresses that the distance between the lower leg and the bottom fork tree must be greater than the total possible travel of the fork. Extreme failure can occur if the lower leg is able to crash into the fork tree! The Speed King fork job is finished and Jeff is well on his way to another clean build.

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