2

During a stroke, I encounter one or two (not always in the same pedal position) where the resistance is high. If I spin the crank freely (on the bike, wheel off ground), it will quickly come to a stop at one of these points. So, part of the stroke is fine. At these points, spinning the cranks backwards, the chain seem to collapse at the top. I feel like maybe the back cassette isn't spinning as free as it should.

Does anyone have any idea of what this could be? I feel I take good care of my bike. Cleaning it from dirt about once per week and degreasing/greasing the chain typically twice per month.

I'm fairly new to bike repairs so any help and pointers are appreciated. Note: The bike is fairly new; only about a month old. I've ridden about 2500 km.

  • 2
    We need some more information on the type of bike. If for instance this is a single speed the reason could be an over tensioned chain. – Carel Sep 29 '20 at 10:57
  • It is a Merida Mission Road 300: Casette: Shimano CS-HG500, 12-28 T Drive train: Shimano RS400, 50-34 T - Shimano Pressfit BB71 – Kabel Sep 29 '20 at 11:39
  • Sounds to me like the chain and sprocket are wearing out. Or your indexed derailer needs adjusting. – Daniel R Hicks Sep 29 '20 at 11:48
  • The bike is fairly new. Only about a month. I've ridden about 2500 km. But considering how new and how carefully i ride I still feel wear and tear should not happen yet? Ill look into adjusting the derailleur. Thanks – Kabel Sep 29 '20 at 12:30
  • Kabel, welcome to Stack Exchange. I made a minor edit, because I think you are talking about spinning the cranks (the things that your pedals mount to), rather than just spinning the pedals around their own axles. You can revert the edit if this is actually what you meant. (look for an edit button.) – Weiwen Ng Sep 29 '20 at 13:12
2

Either the rear wheel or the crank bearings are binding at some point in their revolution, or (or possibly there's something going on with the chain). The first thing to do is track down where the problem is.

Check first for obvious stuff, like is the rear wheel out of true and rubbing the brake blocks?

The next easiest thing to do first is take the rear wheel out, remove the quick release skewer and check the bearings. Turn the axle with you fingers, does the axle have a tight spot, do you feel excessive resistance or 'notchiness'? Push and pull the axle about to check for play, if you can feel the axle moving more than a tiny bit there is excessive play.

If the wheel bearings are is OK, check the crank. Most front derailleur cages have a small screw that allow them to be opened and the chain removed. Get the chain out of the cage and off the chainrings (it's awkward but possible). Spin the cranks by hand, again checking for a tight spot, excessive resistance, 'notchiness' and play.

The wheel is the problem fixing it depends on the type of bearings. Some hubs have 'serviceable' bearings that can be disassembled, some have pressed in cartridge bearings. If the crank is the issue, a new bottom bracket is required.

  • Agreed. Another idea is to drop the chain off the chainrings, and either let it rest on the outside of the BB, or let it come off the outside, and will only be through the front mech cage, where OP can simply hold/tape it out of the way while exploring the BB/cranks for play and binding. – Criggie Sep 29 '20 at 12:17
  • I've taken every revolving piece a part and put it back together to test everything in isolation. The rear wheel axle is rubbing against the casette when the release (quick release) is tightened hard (to recommendation). I assume the axle has been slightly bent or the engineering was shit. Is there any adjustment that can be done, or is it straight buying a new one? – Kabel Sep 29 '20 at 14:19
  • @Kabel ok so you traced the issue to the rear wheel hub. The axle cannot rub on the cassette I think that you mean the axle is hitting the free hub body that the cassette mounts on. Either way if the axle end isn’t concentric in the hub the axle is bent or the bearings are severely messed. up. Next step is to discover what kind of hub you have so you can determine how the bearings and axle can be replaced. – Argenti Apparatus Sep 29 '20 at 15:36
  • If the bike is a month old only, you should take it back to the dealer and have the offending part replaced or repaired. It's certainly still covered by warranty. – Carel Sep 29 '20 at 18:23
1

I graciously disagree with the troublshooting approach already mentioned. Not that there is anything wrong with checking the things mentioned, but because the OP described the chain going slack on the top when pedaling backwards, there are other things that should be checked first.

How worn is your chain? probably a lot after 2500km. I have found that a new chain can do wonders even when we don't think it should matter. There are two ways (probably more, but two that I can think of) to measure a chain with out a tool. Method one...use a yard stick. Pin to pin is supposed to be half an inch. Line up a pin with the one inch marker on your yardstick. If, after 20 or 30 inches the pins don't line up any more then you need a new chain. Method 2, use a new chain. Buy a new chain...if you are riding 2500km, you'll need one anyway. Count the links on the old chain and break the new one at the same point. Now hold them next to each other. If you notice more than about half an inch of difference, put the new one on.

If that does not solve your problem, I would take the back wheel out, and spin the cassette backwards. Does it spin OK? If not, that is worthy of a whole new thread. If it spins OK, next check your jockey wheels. Get the chain away from each of them, and make sure they spin freely.

WHile you have the wheel off, it is worth pulling the chain off the crank, and checking to see that it (the crank) spins freely. Because of the chain slack at the top, I think the problem is not here, but it is worth checking.

Another thing to check. With the wheel in, and chain on, pedaling backwards...does the chain come off the the jockey wheel and get wedged in the derailleur?

If you still have this problem, or you want to ask me to clarify something, by all means reach out. I love fixing bikes, even if indirect.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.