Bike Tech

We here at LRB have recently been receiving letters asking us how to do Bondo body filler modifications to customize bike frames. So we paid a visit to Joseph Garcia at the Drag-N-Shop in Santa Fe Springs, California, to see if he would give us a crash course in Bondo Basics 101. Joseph happily agreed to share a little bit of his expertise with our readers.

Joseph took out all of the tools that he was going to need: cardboard, thin-gauge sheet metal, cutting shears, welder, grinder and sanding wheel. When we asked Joseph what were the "basics," he replied, "The basics are knowing how to start off with a simple, basic tank. Once you know how to do a basic tank, customizing a tank will be a cinch."

So in order to help those readers who want to know how to apply Bondo to their bikes, we brought back some pictures from our class taught by Mr. Garcia. When you think that you've learned all that you need to learn, go out there and try slapping on some Bondo yourself.

Here is a stock Aztlan Cruiser frame from Aztlan Bicycle ready to undergo some minor body modifications.		The first thing that Joseph did was make a stencil of the tank shape out of cardboard. He then applied the stencil to some sheet metal and traced the outline, enabling him to cut out an almost perfect tank.		Here Joseph uses metal shears to cut out the shape of the tank.
Here are the pieces after being cut out, note that the center bottom piece has a slight curve in order to fit the shape of the lower supporting bar. Also note that the right and left sides are distinctly marked to avoid confusion.		After all the pieces were cut out, it was then time to move on to the bodywork. Joseph started off by sanding off some of the paint with a sanding wheel. Doing this allows the sheet metal to "stick" onto the frame when it's time to weld.		The next step was to lay the cut-out pattern in place; check it out, it almost fits like a glove.
Once the frame was grounded, it was time to fire up the welder and do some spot welding. You have to spot weld, because if you don't, the heat might warp the frame and make it almost impossible to fix.		Here's a little secret that Joseph shared with us. In order to get the sheet metal tight in this section of the frame, he used some visegrips to pinch the sheet metal to the frame.		Once both sides of the frame were spot welded in place, it was time to do the bottom centerpiece. Once again, Joseph sanded off some of the paint in order to get a better weld.
After spot welding the piece, it was time to do some serious welding. Joseph decided to start off on the bottom center piece since he was already there. Welding can be hazardous to your health, as you can see by the sparks flying everywhere.		Grinding down the weld beads is a must, in order to get the sheet metal as tight as possible to the frame without breaking the weld. And make sure to clamp down the frame to something; you don't want that thing flying around.		After we took a quick snack break, it was time to move on to the right side of the tank. The master metal arts man followed the same steps that he took for the bottom centerpiece.
Once again, Joseph grabbed his grinder and ground the weld beads down to the frame.		With all of the welding out of the way, we quickly prepped the frame for Bondo. Joseph once again used his sanding wheel on the sheet metal to allow the plastic body filler to stick to the frame. Avoiding this step might cause your Bondo to not stick to the frame or, worse, crack and fall off after you've painted your frame.		Slap some plastic filler onto a piece of cardboard or better yet a mixing tray.
Using a keen eye for this step, Joseph added just the right amount of hardener to the filler. Don't use too much! If you do, the filler won't harden.		Joseph mixes the filler and hardener with his palm-size spatula. Joseph does this until the two components turn a pinkish color.		Don't be afraid to get the filler all over the place. Unless your mom or dad are yelling at you, it's okay.
Joseph made sure to spread the filler throughout the tank thickly and evenly.		Joseph was on the home stretch; he used 40-grip paper (left side) and 80-grip paper (on the right) to sand down the filler.		After big Joe got his arm in motion there was no stopping him. Taking down all of the lumps and smoothing out the frame was his primary goal for the day.
Check it out the frame; looks pretty custom, doesn't it?		The last step that Joseph took was to add some primer. This allowed him to see any imperfections. Looking over the bike very carefully under a magnifying glass, Joseph noticed some minor details that had to be fixed. He then poured a little more filler out onto the mixing tray and quickly fixed the flaws in a matter of minutes. This Bondo Basics class was now over, and our homework for the day was to go home and try this on a spare bike frame.

REMEMBER: Always do any work like this one under adult supervision and always wear safety equipment.