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Resistance against cranks, but not to rear wheel.

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Resistance against cranks, but not to rear wheel.

Old 04-07-18, 05:19 PM
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martial
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Resistance against cranks, but not to rear wheel.

Hello, everyone—a bit of a puzzle to offer here, for which I’d greatly appreciate your advice.

The bicycle is a single-speed copy of a Raleigh DL-1, likely from the ’eighties, called a Yongjiu (Forever) PA-17. I have ridden it around 1,500 mi. since I got it last Summer. It seems to have been used minimally before then.

The problem: I recently had both the front and rear wheel trued because of a kink in the front wheel. Now the once silk-smooth pedaling offers some resistance. It is almost imperceptible while actually pedaling, but I now find after each 5-mile leg of my daily commute that I am much more tired. Investigation of the BB has revealed that, as I push the cranks, there is a slight resistance roughly twice every revolution, but it seems that the resistance is not in the same spot each time. But it is difficult to tell.

I have all but eliminated the BB as the problem: I detached the chain and very slowly turned the cranks. It seemed smooth.

Earlier, I adjusted the axle-tensioners to give the chain more slack. No change.

I removed the rear wheel to check the flywheel. It seems to spin smoothly, so far as I can tell spinning it with my fingers.

Strangest of of all is that the rear wheel spins freely when coasting, but I still feel periodic resistance when I move the cranks slower than would propel the already-moving wheel.

Where, then, is the problem?


My hypothesis (which I will test when I have time): The flywheel wobbles a little. Maybe the wheel is sitting askew so that the inside of the flywheel is rubbing against the full chain case.

My questions are, (1) What are some likely causes, and (2) is there anything more I can do than simply to adjust the axle-tensioners and perhaps bend the chain-case To reduce friction with the flywheel?

Thanks in advance!
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Old 04-07-18, 07:05 PM
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McBTC
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Is your tire rubbing against the frame?
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Old 04-07-18, 07:14 PM
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I think your chain is too tight and is tightening and loosening as the slight (normal) eccentricities of the chain wheel and cog interact. The chain should have no tension at the tightest point. You may need to turn the cranks a few times to find this point since the drive is not 1:1.
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Old 04-08-18, 06:40 AM
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...and the part in the back is a freewheel.
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There's no such thing as a routine repair.

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Please respect others by taking the time to post clearly so we can answer quickly. All lowercase and multiple typos makes for a hard read. Thanks!
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Old 04-08-18, 08:20 AM
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As mentioned above, chain tension would be the obvious culprit.
If you've already slackened the chain by moving the rear wheel forward in the dropouts, and there was no improvement, then it's unlikely that chain tension is to blame. Make sure, as dsbrantjr suggested, that the chain is not super-tight at any point through multiple rotations.

Since the problem occurred after having the wheels trued, I suspect that the wheel is deflecting under load, ie: when you're riding, and your weight is on it, and either the rim is rubbing the brake (if you have a rear brake) or the tire is rubbing the frame, as mentioned by McBTC. Look for a shiny spot inside the chainstays, or back off the brake adjustment, accordingly. If the wheel is indeed deflecting, it sounds like spoke tension was decreased in order to help true out a bad spot in the wheel. Look for a couple floppy spokes, and there will be a very tight spoke between them if this is the case.

Btw, the way to check the BB is to pop the crankarms off, and spin the spindle with your fingers. Bad bearings will become very noticeable without the mass of the cranks adding inertia. You will need a crankarm puller if you don't have one.
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Old 04-08-18, 08:45 AM
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OP eliminated the "under load" theory by soft-pedaling, and still feeling the resistance twice per pedal cycle. My money is on an oval chainring, loosen the chain as roadwing suggested. Also check the chain over.
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Old 04-08-18, 09:25 AM
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I should have been more clear- I was suggesting that the issue, if it occurs only while riding, and not in the repair stand, might be due to rider weight. It's possible for the rim of a badly tensioned wheel to move axially.
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Old 04-08-18, 10:24 AM
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Thank you for all your replies.

Well, I was working on it this morning, as here's what I have:~

Per roadwing, it is almost certainly not rider weight. The steel rims do deflect a little, but I am certain that they do not rub the brake shoes. Per MtBCT, the tire is not rubbing the frame anywhere.

I see that it would be better to test the BB by removing the chain and cranks altogether, but as it's a full chain case with cottered cranks, removing them and reinstalling them would be a real pain! Still, by disengaging the chain from the chainring and turning the cranks at the spindle, I can at least tell that there is less resistance, and no unevenness, than when the chain is engaged. So even if the BB were not perfect, it seems it couldn't be the cause of the periodic tension.

That seems to leave us with dsbrantjr's and wphamilton's advice, to check the chain. I've loosened and tightened the axle-tensioners repeatedly, with no result: there's still periodic tension. Does that eliminate the chain as culprit? What more in the chain should be checked?

And if it is not the chain, does that leave just the freewheel, which I only tested by hand? (Apologies about the terminology. It is literally called 'flying wheel' in the language of this bicycle's origin!) Perhaps there is a little unevenness in the chain and a tiny wobble in the freewheel, and together they add up to periodic tension against the chainring?

Thank you again.

Last edited by martial; 04-08-18 at 10:31 AM.
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Old 04-08-18, 12:30 PM
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Originally Posted by martial View Post
That seems to leave us with dsbrantjr's and wphamilton's advice, to check the chain.
I think you left out the most likely culprit: the chain ring being out of round. Slightly oval shaped will increase the tension twice every revolution.

Regarding the chain, I am thinking of a stiff link that doesn't bend freely. It should be easy to spot.
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Old 04-08-18, 02:04 PM
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Originally Posted by martial View Post
Thank you for all your replies.

Well, I was working on it this morning, as here's what I have:~

Per roadwing, it is almost certainly not rider weight. The steel rims do deflect a little, but I am certain that they do not rub the brake shoes. Per MtBCT, the tire is not rubbing the frame anywhere.

I see that it would be better to test the BB by removing the chain and cranks altogether, but as it's a full chain case with cottered cranks, removing them and reinstalling them would be a real pain! Still, by disengaging the chain from the chainring and turning the cranks at the spindle, I can at least tell that there is less resistance, and no unevenness, than when the chain is engaged. So even if the BB were not perfect, it seems it couldn't be the cause of the periodic tension.

That seems to leave us with dsbrantjr's and wphamilton's advice, to check the chain. I've loosened and tightened the axle-tensioners repeatedly, with no result: there's still periodic tension. Does that eliminate the chain as culprit? What more in the chain should be checked?

And if it is not the chain, does that leave just the freewheel, which I only tested by hand? (Apologies about the terminology. It is literally called 'flying wheel' in the language of this bicycle's origin!) Perhaps there is a little unevenness in the chain and a tiny wobble in the freewheel, and together they add up to periodic tension against the chainring?

Thank you again.
Dsbrantjr probably recognizes that you have already slackened the chain some and recommends that you slacken it more -- to the correct amount. You could follow his direction or any directions of many posted in this forum and elsewhere.
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Old 04-08-18, 02:24 PM
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When is the last time you cleaned and greased the bearings in the wheels?
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