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I have a Giant Esprit Twist Power electric bike, which apart from not having nearly enough words in its name also has a problem related to the crank.

When I put a lot of load through the pedals there is a loud clanking sound, once per pedal-press. If, as I cycle, I press with just one foot (and just lightly follow-through with the other) then I get the noise once and then not again until I start pressing with the other foot. This suggests to me that the problem is related to something shifting position in response to the side of the bike on which the pedalling force occurs.

Curiously, although the noise is extremely pronounced, I don't think I can feel anything.

There is no play I can feel in the bottom bracket, and likewise the pedals seem to spin smoothly.

The torque-sensing chainset arrangement seems like a possible source for the noise, I'm just not sure how.

So I guess my questions are...

  1. Can a bottom bracket bearing make this kind of noise without feeling rough or loose?
  2. Does anyone have any advice to offer about this kind of torque plate?

Here is a picture of the dismantled torque-plate:

Giant electric bike torque plate / chainset combo

Thanks in advance!

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  • Is it possible it has a clutch and that is what is making the noise? Can you hold the brakes and have it make the sound from a stand still? If so I would have a friend or set up a camera to watch it and better pinpoint the source of the sound.
    – FreakyDan
    Commented Mar 26, 2015 at 17:37
  • It's not too uncommon for a slightly loose bottom bracket cartridge to slip back and forth as you crank and make such noises. Generally the cartridge it not loose enough that it feels loose on casual examination. But I would be most suspicious of that torque thingie.
    – Daniel R Hicks
    Commented Apr 22, 2015 at 1:42
  • Having taken it apart, I'm certain there is no clutch mechanism within the crank assembly. The suggestion that it could be the bottom-bracket cartridge moving a little sounds very plausible to me, but unfortunately I've hit a dead-end there too because the lock-rings for it don't seem to match up with any standard bike tool. I'll try Giant and see if they can offer any advice. Thanks all for your help.
    – Martin
    Commented Apr 22, 2015 at 17:42
  • How could there be no clutch mechanism? Without a clutch starting and stopping would be extremely abrupt and would likely stall the motor. Those springs in the photo sure look like part of a centrifugal clutch.
    – Carey Gregory
    Commented May 21, 2015 at 17:17
  • @CareyGregory is it not a hub motor? And that torque plate sites under the cranks. The bike motors I've seen tend to use a soft start and they cut out on a switch in the brake levers. Starting in throttle mode and stopping pedaling to coast can be a little jerky but nothing major.
    – Chris H
    Commented May 21, 2015 at 20:35

1 Answer 1

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That crank is unusual and therefore it is hard to give you advice.

It shouldn't be the bearings because they don't usually make a big noise, but rather make the crank harder to move around (you can perfectly feel bad bearings if you try moving it with your hand and feel resistance/side-to-side movement).

Can you install the crank without the clutch mechanism, or simply install another crank, and test if the noise goes away? My bet is it will :)

If the noise goes away, the best is to contact Giant support or a representative and see what they can do for you (send you new pieces, help troubleshooting, etc). If they can't do anything for you, at least ask them to advise on a solution, or to suggest a list of cranks that are compatible with the electric system, in case a normal crank does not work.

While testing keep in mind this can be a malfunction piece which might fail to perform at the worst possible moment, so take it easy. Good luck.

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