I came across a bike blog from Taiwan that happened to be linked to my blog; it showed a picture of a bike with a strange looking fork. The writer speculated whether it was a custom fork.
It was custom alright, but by accident rather than design. The rider had run into something solid, (Probably a car.) and bent the fork back.
To give this rider credit for ingenuity, it looks like he simply turned the fork around (Backwards.) and carried on riding.
Over the years I straightened many steel forks like this one, with complete safety and often not even damaging the paint. When you consider that a fork blade starts out as a straight tube; it is then rolled in a machine between rollers to make it tapered. This process is done cold.
The top end is pressed to an oval shape; this is also done cold. Finally the framebuilder cold bends the fork blade to the desired curve. So if the fork blade is bent once more in an accident, it can be re-straightened cold with complete safety as long as the tube is not kinked or rippled.
I would not recommend that this be done multiple times but once is okay. I will explain how it can be done.
My fork blade straightening tool was a piece of one inch steel (Sometimes called black iron.) gas or water pipe about four feet long. One inch pipe measures 1 in. dia. on the inside, and is about 1 ¼ in. on the outside. (Picture right.)
I also cut a 1 in. piece of this same pipe then cut it in half to form a “C.” This was then welded to the top of the four foot length of pipe, and would form a cup to go around the fork blade near the crown.
This was padded on the inside of the “C” with several layers of duct tape to protect the paint.
Next take a piece of old bicycle chain about 10 inches long, make a loop by joining the ends using a chain rivet tool.
The fork needs to be removed from the frame; hold the steering column horizontally in a vise that is solid and won’t move.
Position the bent fork blades so they are sticking out horizontally on one side of the vise; left or right depending on which hand you use. Right side if you are right handed.
The fork should also be positioned so the blades are one above the other, and the bend that you are about to straighten is away from you.
Straighten one blade at a time by placing the chain loop over your four foot piece of pipe, and the other end of the loop over the fork tips. Place the “C” cup up near the crown above the bend, hold in place with one hand, and pull towards you with the other hand to straighten. Repeat to straighten the other blade.
Now you will need to align the fork. I had a surface table with a fixture to hold the fork. However, most people will not have this luxury, so here is the next best thing. You need to make or have made another tool consisting of a piece of 7/8 inch solid steel bar, about 24 inches long. (Picture left.)
Turn down in a lathe 18 inches of this bar to a smaller diameter, about ½ or 9/16 of an inch. (Leaving 6 inches at 7/8 dia.)
It does not have to be exact as long as it is small enough to pass easily through the butted end of the steering column. 7/8 in. is the diameter of a quill stem. (I am assuming this is an older steel frame with a one inch steering column.)
Slide the 7/8 in. portion into the steerer with the smaller diameter length reaching down between the fork tips. You now have a reference point that is dead center of your fork.
Ideally place a front wheel spindle between the fork tips, but failing that you can use a piece of steel bar 5/16 or 9mm. dia., or even a pencil at a pinch.
The fork tips need to be 100mm. apart, (Measured on the inside.) and centered on your special steel bar you have placed in your steerer.
The fork tips need to be in the same plane as the fork crown; a straight edge across the fork blades up near the crown can be sighted with your wheel spindle, or whatever you have between your fork tips. The fork rake or offset can be measured from the bar to the wheel spindle.
Also the straight part of the fork blades before the curve starts can be checked by placing a straight edge on both the front and back of the blades to see if the steel bar is centered.
In a front end shunt like this, the top and/or downtube sometimes get rippled. If this is the case the tubes need replacing as they will eventually break. The good thing about a steel frame is that it will rarely fail suddenly, but a crack will appear first and the frame will start to feel “spongy” as a warning before it fails completely.