FENDER - Repair

Fender is the US English term for the part of an automobile, motorcycle or other vehicle body that frames a wheel well (the fender underside). Its primary purpose is to prevent sand, mud, rocks, liquids, and other road spray from being thrown into the air by the rotating tire. Fenders are typically rigid and can be damaged by contact with the road surface. Instead flexible mud flaps are used close to the ground where contact may be possible.
Sticky materials such as mud may adhere to the smooth outer tire surface, while smooth loose objects such as stones can become temporarily embedded in the tread grooves as the tire rolls over the ground. These materials can be ejected from the surface of the tire at high velocity as the tire imparts kinetic energy to the attached objects. For a vehicle moving forward, the top of the tire is rotating upward and forward, and can throw objects into the air at other vehicles or pedestrians in front of the vehicle. http://en.wikipedia.org

REPAIR:

Fender bumping and repairing is not as difficult a job as the damaged metal might indicate. A good job is largely a matter of studying the bump or jam and selecting the proper tools to work the bump out.


1. Clean the fender thoroughly with an oil-soaked rag. The purpose of the oil is twofold: first, to reflect the light onto the damaged section, so that every bump and indentation may be readily seen; second, the oil creates a cushion under the hammer and keeps the paint from being picked up by the hammer.

2. Clean the underside of the fender of all grit, tar, and clinging dirt particles. If this is not done, these particles will be beaten into the metal when the hammer and dolly block are used.

3. Rough out the jam, using the proper dolly block. Follow the crown of the fender when roughing out this jam. Never use a ball peen hammer to rough out a jammed fender or the metal will be full of small "bubbles" and a smooth job will be an impossibility. Selection of the proper dolly block will greatly simplify this operation, because the right block has the same contour as the fender had before it was jammed.

The jam at the rear of the fender shows that the rear skirt has been pulled out and also that the rear corner section is pulled out, making a series of short tight jams. The best method of roughing out short, tight jams is to use two dolly blocks, one held on the bead of the fender to relieve vibrations and the other to rough out the bump.

4. After roughing out these tight jams, bring the skirt back into alignment by holding a dolly block behind the low spot and the skirt and hammering the skirt back.Hot metal shrinkage will draw the skirt of the fender in and make it rigid. Then, in the centre of the stretched part of the crown, at the highest point of the bulge and about 2 inches up from the bead apply hot shrinkage.

Caution: The pressure must be applied to the rear of the fender throughout the entire hot shrinkage process.
If there are any breaks or cracks in the fender they must be welded before the hot shrinkage operation.

5. Bump out the shrunk section, using a dolly block and a bumping hammer or mallet. Hold the dolly block loosely on the low spots underneath the fender and strike the high spots on the outside with the hammer or mallet. This method causes the dolly to spring back against the low spots and readily smooth them out.
If the fender does not set square or is not shrunk enough, apply more pressure and repeat the process. Always heat on the highest part of the bulge.

6. To bring the bead into perfect alignment, hold a dolly block behind the low spots and strike the high spots on the bead with a mallet or bumping hammer.
To show up the high and low spots on the rough bumped sections, use a long piece of chalk and holding it flat on the metal, rub the chalk on these sections. The high spots will show up as being white with chalk while the low spots will be dark or unchalked. Do not file yet.

The metal may now be finished and prepared for painting with a file and disk sander. At the time the file is being used, any small indentations will show up and may be easily tapped out.