[CR]Re: Bottom Bracket repairs

(Example: Framebuilding:Norris Lockley)

Date: Fri, 4 Apr 2003 07:59:05 -0800 (PST)
From: "Bruce Schrader" <bcschrader@yahoo.com>
To: classicrendezvous@bikelist.org
In-Reply-To: <CATFOODvcDfSDGAIXWb00000cdf@catfood.nt.phred.org>
Subject: [CR]Re: Bottom Bracket repairs

Bottom brackets are usually made of mild steel whether cast or forged or stamped, so welding (gas or tig) the shell is my preferred method of repairing the threaded portion or the underside.

I recently saved a Hetchins from the grave and it was very satisfying indeed. Someone had stolen the bike and was stripping the components off it. They obviously didn't know anything about the value of the frame or much about bikes. They had tried to hack saw through the bottom bracket to remove the crank arms. They sawed about 2/3 of the way around the shell only to discover when they hit the cup inside that the saw wouldn't touch it...to hard. So after several attempts and virtually destroying the bottom bracket, they gave up.

The owner was sick and my heart went out to him as well. It initially appeared to me that the bottom bracket would have to be replaced to salvage the frame. The bottom bracket is IMHO the most difficult piece of a frame to replace due to it's mass and the number of tubes that connect to it.

After pondering the situation for some time, I came up with a plan to save it. I first threaded a crank tap backwards all the way into the center of the shell. This was so I could use the remaining threads as pilot threads later on. Then I carefully gas welded the shell, laying multiple beads of steel on top of each other to build the shell back up to its original shape. This was all done well away from the brazed tubes so no damage was done to the brazing and the expensive tap inside didn't get too much heat either. After building up the shell, I connected the tap handle to the tap inside the shell and tapped new threads using the existing threads as a guide and running from the inside out. They came out perfect. After that, I filed the outer surface to match the original shell and refaced the outer edge. When done, it was impossible to tell that anything had ever been damaged.

I've also welded cracks or seams that let go in bottom brackets. These are usually on the underside of the shell and away from the tubes which makes it easier.

If a crack appears in the tube (usually the seat or downtube) near the bottom bracket, then the tube should be replaced.

I have also salvaged bottom brackets where the threads have been damaged or destroyed. I braze (bronze) the threaded area and re-tap the shell. Usually, people will re-tap an English shell to Italian threads to save it, but IMHO, the increase in size from English to Italian is not enough to provide a good set of threads and I like to keep the English and Italian stuff separate anyway. Bronze is quite sturdy and makes good threads where silver is too soft and doesn't build up as well.

Of coarse, the paint on the bottom bracket is burned away while performing any of the above mentioned procedures so my methods of repairing do not preserve a beautiful or original paint job.

Bruce Schrader San Francisco

===== "Not all those that wander are lost." -J.R.R. Tolkien (1892-1973)

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