Monday, March 06, 2006

Rear Dropouts

Have you ever had the misfortune to break an adjuster screw in a rear dropout? Or worse still a thread tap which is hardened and can’t be drilled out.

The best way to deal with this problem is to seek out an engineering company who have Electrical Discharge Machining (EDM) equipment. This machine can burn through steel with precision using very little heat. I would occasionally break a tap in the dropout of a brand new painted and finished frame. I would take it to a local EDM shop where they would burn out the broken tap and not even touch or mar the paint work, and not charge me too much money.

On another subject have you ever wondered what those two little threaded holes are for in the right hand side Campagnolo short rear dropout. Mostly seen on frames built through the 1980s. (See the picture above.)

This was for a special chain hanger introduced in 1977. (Portacatena) It consisted of a “C” shaped steel plate that attached to the inside of the rear dropout with two screws in the threaded holes. The idea was in the event of a flat tire, with the aid of a special extra lever on your down tube shift lever, the chain could be shifted onto the Portacatena chain holder where it would stay while the wheel was being changed.

After the wheel had been changed the rider got a push start and then shifted the chain onto the rear freewheel cluster in the usual way. The idea never really caught on because it was only suited to a race team with support kind of situation. It was also necessary to use a five-speed cluster on a six-speed hub spacing (125mm.)

Soon after its introduction six speed freewheels became commonplace and the idea died a natural death. In spite of this Campagnola continued to produce rear dropouts with these two threaded holes to my knowledge through the early 1990s. Why? I have no idea.

1 comment:

Anonymous said...

Undoubtedly Campagnolo continued to produce the porta catena holes in the rear dropout because they realized that it would satisfy a continuing need : the drillium craze !!