Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at firstname.lastname@example.org. Today’s column offers tips on eliminating knocking sounds coming from headsets.
Question: I have a carbon road frame with 1.5″ lower bearing and 1-1/8″ upper Campag type internal bearings mated to a fork with a carbon steerer tube. Although the headset is well tensioned and the headset isn’t loose when stationary, I get a knocking sound from the upper bearing under certain loads. It’s not coming from the cables, stem, fork, or bars.
Originally I assembled the headset with some bearing grease around the outside of the cartridge bearing races. I have since cleaned the frame’s 45 degree seat, fork steerer and the outside of the bearing and am trying some carbon paste grease. I am also applying it between stem and steer tube. I am hoping this may help to prevent the bearing from moving on its seat within the frame.
Can you please advise me on this and if it’s the right approach, or is there something else I should know? From: Vlad
Answer: I’ve seen this type of problem arise from headset spacers or stems that are improperly machined, although I suspect that this is not the case on a bike of this caliber. If you are using machined out carbon spacers, like those found on most Specialized bikes, you might try spacers that are a little more robust. On a similar note, instead of using four 5mm spacers, you could try one 20mm spacer. This will eliminate the possibility of rubbing between the spacers. If you have a carbon headset cap (the part that rests on the split ring in the upper assembly), most are very poorly manufactured. Trying an aluminum one could help.
A different split ring could work as well. If the steerer or the split ring is undersized, it might not be clamping down on the steerer with enough force to hold it in place under higher loads.
The carbon paste on the bearing cartridge and steerer is worth a shot, but it might just lead to a crunchy sound when things start moving instead of a knock. I would go with some very thick grease, such as automotive axle grease. This would be my last resort however, because you don’t want to mask an underlying problem that could be fixed with the proper parts.
For any readers out there that want to learn how to adjust or tighten your bike’s headset, check out the video below for instructions.
Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.