Bicycle and motorcycle frames are made from welded tube steel or metal alloy. Aggressive riding and spills can result in cracks at any of the welded joins. Most cracks occur where the frame joins the steering headset or the seat tubes. Cracks where the frame connects to a bottom bracket are common with bicycles. With the exception of carbon fiber bicycle frames that require epoxy, cracks can be fixed and the structural integrity of the frame restored. Those who have mechanical aptitude and knowledge of welding equipment can fix cracks in a bicycle or motorcycle frame.
Bicycle Frames
Step 1
Stabilize the bicycle on a stand or on wood blocks. If the frame is cracked where it meets the steering headset, disconnect the cables from the hand levers and shifter, remove the handlebars and drop the front forks out of the headset. For cracks at the bottom bracket, remove the crank arms, front sprocket, the bottom bracket and derailleur. Remove the seat and rear wheel when fixing cracks at the seat tube.
Step 2
Put on safety glasses and work gloves. Chip away thin and broken portions of the cracked weld with the point of a welding hammer.
Step 3
Set up a power drill with a fine wire wheel attachment. Using moderate pressure on the wire wheel, remove the paint at the weld and the adjacent portion of the headset, seat tube or the bottom bracket.
Step 4
Put a welding mask and protective gear on and ignite the welding torch. Make a single, continuous weld to fix the crack. Puddle the weld as evenly as possible and allow it to cool completely. Touch up the weld using a round file before repainting or reassembling the bike.
Motorcycle Frames
Step 1
Stabilize the bike on a stand or the center kickstand. Remove the seat and disconnect the battery cables. Remove the battery. Disconnect the fuel lines and remove the gas tank, carburetor and the fuel pump. Remove the handlebars and drop the front forts to fix a crack at the steering headset. Remove the rear wheel to fix a crack at the base of a rear frame section.
Step 2
Disconnect and move any wires, hoses and vent tubes away from the area of the repair. Use a welding blanket to protect any adjacent electrical ignition components.
Step 3
Put on your safety glasses and work gloves. Chip away thin and broken portions of the cracked weld using a welding hammer.
Step 4
Set up a power drill with a fine wire wheel attachment. Remove the paint at the weld and the adjacent portion of the headset or frame using moderate pressure on the wire wheel.
Step 5
Don a welding mask and protective gear and ignite the welding torch. To fix a complete disconnection, spot-weld the connection at three places. Make a single, continuous weld to fix the crack. Puddle the weld as evenly as possible and allow it to cool completely. Touch up the weld using a round file before repainting or reassembling the motorcycle.
Tips and Warnings
- Refer to your service manual regarding procedures for removing components, if necessary.
- Do not attempt to straighten steel, aluminum or titanium frames. Enlist a qualified frame builder who has jigs and equipment needed to straighten bent frames.
Things You'll Need
- Safety glasses
- Work gloves
- Metric tools
- Power drill
- Wire wheel attachment
- Welding mask and protective gear
- Welding blanket
- Welding equipment
- Round file
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