If bicycle handlebars move suddenly, a rider can lose control and fall. There are several ways to prevent this through the use of shims or adhesives. Knurling, or making ridges in the metal for a firmer grip, is not recommended because it can produce defects that may cause the handlebar to crack. The handlebar and stem should be measured carefully before assembling the parts. Each method of securing the handlebar involves more complicated disassembly, if subsequent maintenance is necessary. Please be aware that this pertains to aluminium and steel handlebars and stems. Carbon fibre handlebars must be installed per the manufacturer's specifications.
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Things you need
- Vernier caliper with 0.1mm accuracy
- Soda can
- Metal shears
- Thread locker
Loosen the handlebar binder bolt on a conventional stem, and slide the handlebar out to one side. Inspect it for any black streaks that indicate powdered aluminium from the friction of the parts. Clean both the stem and handlebar with alcohol.
Measure the handlebar and stem with a pair of vernier calipers. The internal diameter of the stem opening should be equal to or just slightly greater than the handlebar. In some cases, like old French handlebars, the gap will be large and the stem simply won't bind on the handlebar. With properly fitting handlebars and stems, it is sometimes necessary to spread the stem slightly with a screwdriver as the bar is inserted.
Cut a shim from a soda can with the metal shears. Cut it slightly narrower than the stem so the edges don't slice your hands. Curl the shim up and slide it between the handlebar and stem. Be careful as the edges are extremely sharp. Tighten the binder bolt and test the handlebar for tightness by putting your full weight on the drops.
Apply a thread locking compound between the handlebar and stem. Dis-assemble the parts and apply a thin film of thread locker to the handlebar. Slide it back into the stem and tighten the binder bolt. Allow the thread locker to cure for 24 hours before testing the assembly for tightness. Be aware that disassembling these parts will require heat and considerable force.
Apply high-strength epoxy -- if all else fails -- and reassemble the parts. Allow the epoxy to cure for 24 to 48 hours. Once it cures, disassembling the parts will be almost impossible, so be certain the bar is in the correct position.
Tips and warnings
- Avoid getting adhesives on the threads of the binder bolt. Apply a thin coat of grease and even epoxy will not stick to it. Grease makes it easier to disassemble the next time.
- Carefully inspect the bars and stem for tiny cracks or scratches that could develop into larger cracks. Look for bends, sags or bulges where the bars enter the stem. If any defects are found, replace the parts.
- If you have a carbon fibre handlebar, install it according to the manufacturer's specifications. Pay special attention to the rated torque for the binder bolts.
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