October 2006 update--   DISASTER STRIKES!

by Mark Rehorst

http://mark.rehorst.com

After riding a total of about 1200 miles on the bike since I completed it, the epoxy joint between the bridge piece and the rear wheel stays failed!  Fortunately, I was only riding at about 3 mph on the sidewalk about a block from home.  The only thing injured besides the bike was my pride.

  

The failure occurred because the bridge piece was epoxied to the bottom side of the stays in order to clear the chain, and the shock absorber was pressing down on it all the time.  After miles of pounding (and riding off curbs with 20 lbs of books loaded in the trunk) it finally gave in.

I decided I needed to make a bridge that attached to the top side of the stays so that the shock absorber would be compressing the joint instead of trying to pull it apart.  I came up with a design, cut a scale model out of cardboard to test fit and everything looked good so I made the part from 1/4" aluminum plate.

I epoxied the plate to the top side of the stays with a layer of glass cloth between the aluminum and CF to prevent corrosion, and filleted the edges.  Then I wrapped it with 2" wide Kevlar tape, loaded it with epoxy, and vacuum bagged it to squeeze out excess epoxy.  The Kevlar will hold the bridge in place in case the joint between the aluminum and CF ever fails.

I reassembled the bike and took care of a few annoying little problems I was having in the process.  Now the bike is better than ever!  The repair process took about two weeks including designing the bridge and waiting for the Kevlar tape to arrive.  The photo below shows the new rear end of the bike.  The yellow stuff is the Kevlar tape which I will soon be painting black for protection from UV radiation.

 

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