Saturday, October 12, 2013

Scorcher Project - Preparing the Strumey-Archer X-RC5(W) Hub

I will be using a modern (Sun Race) Sturmey-Archer hub, X-RC5(W) for this project.

This is a 5-speed, coaster brake, wide ratio hub.  I'm using a coaster brake model to eliminate all of the brakes and cables, giving the Scorcher a clean, minimalistic, appearance.  In this hub third gear is direct drive (1.0 ratio), with two lower gears, .75 and .625 reductions respectively, and two higher gears of 1.33 and 1.6.  The three middle gear ratios are very close to those of a classic Sturmey-Archer 3-speed AW hub.  The hub came from the factory with a 3/32", 18 tooth cog.  Since I will be using it with the original 1970 Sports 48 tooth chain wheel which is made for a 1/8" wide chain, I replaced the cog with a 1/8", 22 tooth, which will provide a lower overall gear range, with the middle three gear ratios similar to what I'm use to when riding a 22 tooth AW hub.  

1/8" 22 tooth cog
This hub has a over-the-locknut distance (O.L.D.), of 127 mm.  This is much wider then the original 110 mm AW that came with the Sports frame.  The use of the wider hub required spreading the rear drop outs to accommodate the increased width of the 127 mm hub.  This was accomplished before sending the frame to be powder coated.  The frame was also modified to accept a Sturmey-Archer indexed shift lever by having friend John braze a shifter boss to the top tube, again this was performed before powder coating.

I knew the wider hub would require adjustments to the chain line on the Sports frame.  Using the method described in my July 2013 post "Adjusting Chain line on the Sturmey-Archer AW hub".  I calculated the front chain line to be 41.3 mm.  Using the hub as configured from the factory I measured the hub and calculated the rear chain line to be 48.5 mm., resulting in a chain line difference of 7 mm.

Since there is really no way to adjust the front chain line with the Raleigh bottom bracket and crank/chain wheel, I would need to move the rear hub chain line to the left.  Unfortunately; this new hub does not have as many adjustment opportunities as a classic AW.  There are no cog spacers or additional spacers on the hub axle that could be re-configured.  It does use a dished cog that can be flipped, but it was already positioned to the inside.  There was a large 5.5 mm thick cone lock-nut on the left brake side of the hub, I replaced it with a standard lock-nut from a AW hub which is only 3 mm thick.  I also added a 3 mm washer to the right side under the cone lock-nut.  Together these adjustments moved the rear chain line to the left by approximately 3.5 mm, but did not significantly change the O.L.D. of the hub so it would still fit within the expanded dropout spacing.  Not perfect but better then the original 7 mm difference.

Original 5.5 mm thick left side lock-nut (top) replaced by thinner AW lock-nut below. 
3 mm washer added on right side below lock-nut.
Next step in the Scorcher project will be wheel lacing.

I've been experiencing some problems with this Blog and interaction with Google+ when commenting and replying.  If someone could please send me a test comment I would appreciate it!  You should be able to comment without having a Google+ profile.

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