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-   -   Cranks moved left? (http://www.bikeforums.net/bicycle-mechanics/936017-cranks-moved-left.html)

Duane Behrens 02-27-14 08:04 PM

Cranks moved left?
 
Hmm. 88 Schwinn World Sport 12-speed. Shimano FD and RD.

I replaced the bottom bracket's caged bearings tonight. No problems, much smoother pedal operation now and with no play. However, upon re-assembly the FD chattered and then sent the chain over the top of the big ring. It's as if the chain rings are now slightly closer to the bottom bracket.

Pretty sure I checked the orientation of the spindle during re-assembly. It appears to be the same length on both sides, the only difference is a raised band inboard of the cone on the drive side. I cleaned it well before re-assembling and applied a bit of grease at all threaded connectors. Did I tighten the right side too much? TIA.

rpenmanparker 02-27-14 08:08 PM

Could you have used bearings larger than what you replaced? That would do it.

hueyhoolihan 02-27-14 08:16 PM

if it is an old style caged bearing BB with a separate spindle, well, some of the spindles are asymmetrical. that would do it, if it were put in backwards, which is easy enough to do.

HillRider 02-27-14 08:32 PM

Quote:

Originally Posted by hueyhoolihan (Post 16533808)
if it is an old style caged bearing BB with a separate spindle, well, some of the spindles are asymmetrical. that would do it, if it were put in backwards, which is easy enough to do.

+1 that's a likely explanation. The usual rule was to install the spindle so that the engraving on it would read correctly from the rider's position if you could see through the bb shell.

However, I had a '92 Trek 7000 MTB that had to have the spindle installed "backwards" (longer side toward the non-drive side) to let the nds crankarm clear it's chainstay. This is very rare.

FBinNY 02-27-14 09:04 PM

Quote:

Originally Posted by Duane Behrens (Post 16533781)
..... However, upon re-assembly the FD chattered and then sent the chain over the top of the big ring. It's as if the chain rings are now slightly closer to the bottom bracket.
.....

Reality check!

From the description it seems that you're talking about a barely noticeable change, evidenced only by overshifting on the FD. So we're talking less than 1mm, maybe only a few 10ths of a millimeter, and there are no other issues.

If that's right, you're greatly over thinking it. The crank may be slightly inboard simply because you pushed it higher on the taper by tightening more than before. So do the normal thing and simply adjust the FD to match the crank. You'll need to adjust the limits, and possibly the chain tension, both of which are minutes of work, and move on.

Duane Behrens 02-27-14 11:38 PM

Double checked the spindle. It was installed correctly. Thanks, though, "Huey," that was my first guess as well.

Checked the bearing size; identical to those removed. Thanks, though "rpen." A good hypothesis.

Went to check the FD. Noticed that each chain ring has a ridge on one side only. (I'd taken them off to clean them.) Went back to the "as purchased" photographs. Realized I had the inside chain ring oriented in reverse; the ridge was on the inboard side. An easy fix and I'll take a bit more care in disassembly next time.

Fortunately, I didn't try to adjust that error out by adjusting the FD. Had I tried that approach, I'd still be out there. Reality check.

Anyway. Thanks for the comments. All appreciated. DB.

shelbyfv 02-28-14 08:12 AM

Your snippy reply to FB is uncalled for. His advice was correct based on the info you gave in your original post. If you recall, you made no mention of having disassembled the crankset. Happy it all worked out for you but don't abandon good manners when you approach the keyboard, you are here asking to learn from others.

rpenmanparker 02-28-14 09:47 AM

Quote:

Originally Posted by shelbyfv (Post 16534778)
Your snippy reply to FB is uncalled for. His advice was correct based on the info you gave in your original post. If you recall, you made no mention of having disassembled the crankset. Happy it all worked out for you but don't abandon good manners when you approach the keyboard, you are here asking to learn from others.

I didn't get that from Duane's reply. I thought he was just being matter of fact. Yes, the disassembly information might have shortened the analysis some, but I didn't sense any lack of gratitude for all the ideas offered.

FBinNY 02-28-14 10:00 AM

Quote:

Originally Posted by shelbyfv (Post 16534778)
Your snippy reply to FB is uncalled for. His advice was correct based on the info you gave in your original post. If you recall, you made no mention of having disassembled the crankset. Happy it all worked out for you but don't abandon good manners when you approach the keyboard, you are here asking to learn from others.

Thanks for the endorsement, but I don't get offended by stuff like this.

My response was based on the fact that the amount of difference was too small to be explained by any change related to a reversed BB or misinstallation. This is why I stated with the reality check reference.

Had the OP mentioned that he also took apart the crank, removing and replacing the rings, probably all responders would have mentioned a reversed ring as a possibility.

One thing is strange though, the OP says the chain overshifted. Since it's very rare to reverse the outer ring, it implies that the outer limit is misadjusted. So either the crank is a hair more inboard, or the limit was slightly off all along.

I cannot repeat enough that the key to getting a decent analysis of a mechanical problem is to provide complete information, which didn't happen here.

HillRider 02-28-14 11:33 AM

Quote:

Originally Posted by FBinNY (Post 16535184)
I cannot repeat enough that the key to getting a decent analysis of a mechanical problem is to provide complete information, which didn't happen here.

This is a very common occurrence here. You get some but not all of the information you need to answer the original question and it takes some real digging to get the rest. This thread wasn't nearly as bad as the ones that start with something like; "My bike won't shift. What should I do?" Fifteen posts later we get the info we should have had at first.

FBinNY 02-28-14 11:47 AM

Quote:

Originally Posted by HillRider (Post 16535550)
This is a very common occurrence here. You get some but not all of the information you need to answer the original question and it takes some real digging to get the rest. This thread wasn't nearly as bad as the ones that start with something like; "My bike won't shift. What should I do?" Fifteen posts later we get the info we should have had at first.

Yes, it's very common which is why I said we cannot say it enough. OTOH, I don't know what's worse. Getting very sketchy info, or getting very detained info that's missing a key bit. The the second is like a magicians slight of hand, focusing attention in the wrong place.

hueyhoolihan 02-28-14 12:59 PM

just goes to show that symmetry, all things being equal, is, in general, a good thing, even lowly chainrings and spindles. simplifies life.

BTW, i confess that even if the OP mentioned that he or she had removed the chainrings, i don't think it would have occurred to me that inadvertently reversing them on reassembly was what was causing the problem.

*scratch head* no i don't. :)

Duane Behrens 03-01-14 09:07 PM

Quote:

Originally Posted by hueyhoolihan (Post 16535895)
just goes to show that symmetry, all things being equal, is, in general, a good thing, even lowly chainrings and spindles. simplifies life.

BTW, i confess that even if the OP mentioned that he or she had removed the chainrings, i don't think it would have occurred to me that inadvertently reversing them on reassembly was what was causing the problem.

*scratch head* no i don't. :)

First off, apologies for any "snippiness." Guess the "REALITY CHECK!" shout struck me as condescending. Silly me.

Second, we were all wrong. Flipping the inside chain ring around didn't help. [insert cuss word here]

Here's more info that should have been included in my first post: a) The bottom bracket spindle was equadistant on both sides. Odd, something I'd never seen. b) the left retaining ring was spinning loose on the left cup threads. The left cup itself was loose as well, which was probably the primary cause of the intermittent chunking I was feeling and hearing down there, and the reason I took it apart.

Okay, now newly armed with a bit more information, I'm in the garage last night trying to correct a chain that, with the new bearings properly adjusted, NOW insists on grinding on the small ring and in the smallest 3 or 4 cogs, getting slightly caught on the large ring before it settled back down onto the small. Unrideable. No adjustment helped. Frustrated, I loaded it up and took it into the LBS with my hat in my hand. As always, the guys at Safety Cycle in Torrance were understanding and helpful, unlike my own insulting bad self (BTW, did I apologize? If not, apologies.)

They called me this morning and I went down for a confab. They'd also tried flipping the rings with no luck. Their proposed fix? They want to order spacers to move the large chain ring farther from the small. What does this have to do with spindle length. :-) I know - nothing. Stay tuned.

hueyhoolihan 03-01-14 09:25 PM

Quote:

Originally Posted by Duane Behrens (Post 16539924)
First off, apologies for any "snippiness." Guess the "REALITY CHECK!" shout struck me as condescending. Silly me.

Second, we were all wrong. Flipping the inside chain ring around didn't help. [insert cuss word here]

Here's more info that should have been included in my first post: a) The bottom bracket spindle was equadistant on both sides. Odd, something I'd never seen. b) the left retaining ring was spinning loose on the left cup threads. The left cup itself was loose as well, which was probably the primary cause of the intermittent chunking I was feeling and hearing down there, and the reason I took it apart.

Okay, now newly armed with a bit more information, I'm in the garage last night trying to correct a chain that, with the new bearings properly adjusted, NOW insists on grinding on the small ring and in the smallest 3 or 4 cogs, getting slightly caught on the large ring before it settled back down onto the small. Unrideable. No adjustment helped. Frustrated, I loaded it up and took it into the LBS with my hat in my hand. As always, the guys at Safety Cycle in Torrance were understanding and helpful, unlike my own insulting bad self (BTW, did I apologize? If not, apologies.)

They called me this morning and I went down for a confab. They'd also tried flipping the rings with no luck. Their proposed fix? They want to order spacers to move the large chain ring farther from the small. What does this have to do with spindle length. :-) I know - nothing. Stay tuned.

the LBS's recommendation strikes me as one kludge on top of another. reminds me of some of the guys i used to work with. instead taking the time to find the root cause, they focused on addressing the symptom, usually introducing additional and more severe problems... this involved software, but the principal is the same. :)

BTW, it sounds like the whole BB, chainring/chainline issue might have been pretty much whacked even before the bearings were replaced.

FBinNY 03-01-14 09:51 PM

Quote:

Originally Posted by hueyhoolihan (Post 16539956)
the LBS's recommendation strikes me as one kludge on top of another. reminds me of some of the guys i used to work with. instead taking the time to find the root cause, they focused on addressing the symptom, usually introducing additional and more severe problems... this involved software, but the principal is the same. :)

+1.

My Reality check, was a reminder that the responses weren't logical based on the report that the chainrings "seemed" to be more inboard than before, and it was time to reconsider the initial premise.

From the description you were talking about too small a change than anything in the BB would produce, and in any case would be addressed by adjusting the FD.

Then you started flipping chainrings, which made as little sense, since most rings have counterbores for the bolt heads and can only be mounted one way.

So, time for another reality check and start from the beginning with ALL the relevant info.

1- did the chain/chainrings and FD work correctly before you started, or are we possibly dealing with something that was this way all along?
2- what is the chainline now? Measure either across to a tube, and add the radius, and/or lay a straightedge (edgewise so there's no flex) against the face of the outer ring on a secant to establish the plane, and carry back to the cassette. Correct for the offset to the centerline between the rings, (usually 8mm or so) and see where it lines up on the cassette.
3- what else did you possibly change? If the system worked before and doesn't now, that is the most important question because stuff doesn't change unless somebody changes it. So the key to the puzzle is what is different now than before? This doesn't apply if the system wasn't working before.
4- what is the distance from the tips of the inner ring teeth and the inside face of the outer ring?
5- what kind of crankset, and what chain?

Increasing chainring separation, may solve a problem you shouldn't have, but unless you did something, or are using a very modern crankset, 6s chainring spacing is already very generous.

Duane Behrens 03-01-14 11:36 PM

1 Attachment(s)
When I get the bike back, I'll check for a countersunk side to the small chain ring. I don't recall seeing one; pretty sure it would have been obvious. Anyway, I eventually sussed out the proper direction by looking at the wear on the teeth. A bit more wear was visible on one side of most teeth, indicating the back side of the rotation. ODDLY, the LBS said I still had it backwards and turned it back the other way. Grinning now. I'll post pictures when I get it back.

The FD and chain rings DID work correctly before I took it apart. However, the BB was clearly loose. Cranks had play and there was an occasional "caChunk" noise from the spindle Which is why I took the BB apart. The bearings were worn - tiny little scars and flattening visible on most of the caged bearings. And as noted, the lock ring was almost off and the lefthand threaded cup was loose.

No other changes, and I didn't try to adjust the RD until after the chainring swap didn't make a difference. Can't take the measurements until the bike comes back. Sugino MP crank. Pic shown is as purchased. Thanks. DB

http://bikeforums.net/attachment.php...hmentid=366710

Duane Behrens 03-09-14 08:40 AM

Want to keep this thread alive.

I picked the bike up from the LBS. The shop foreman said, "It's better, but we're not that happy with it." I took a spin around the shop and immediately understood what he meant. 1) At least it SHIFTS now! :-) Much better than before. Good. (2) And it indexed into all gears properly. (Shimano stem mounted indexed shifter). Good. (3) Unfortunately, it still hesitates when changing the front rings - either way. It's almost as if they're having a noisy committee meeting down there before electing to move the chain onto the desired ring.

"FBinNY" - and all here - thank you again for both your tips and your questions above. I've got both wheels off at the moment - am upgrading the bike with "hand-me-down" wheels and tires from the Nishiki. Once it's cleaned up, I'll take those measurements you've suggested. With gratitude. Best. DB

rpenmanparker 03-09-14 09:09 AM

And FB's advice to just adjust the FD for a ring closer to the BB doesn't work? If that is the case, then sometimes you have to forsake "why" and just do an empirical fix. If a small spacer like 1 mm or less between the fixed cup and the BB shell will take care of your problem after FD re-tuning and not totally screw up your chain line, why not just do it? You can drive yourself crazy trying to figure out the right direction for the rings and other things. No matter how dubious any of us are about woulda, shoulda. or coulda, if a spacer fixes it, isn't that all you care about?

Duane Behrens 03-09-14 06:47 PM

Quote:

Originally Posted by rpenmanparker (Post 16562182)
And FB's advice to just adjust the FD for a ring closer to the BB doesn't work? If that is the case, then sometimes you have to forsake "why" and just do an empirical fix. If a small spacer like 1 mm or less between the fixed cup and the BB shell will take care of your problem after FD re-tuning and not totally screw up your chain line, why not just do it? You can drive yourself crazy trying to figure out the right direction for the rings and other things. No matter how dubious any of us are about woulda, shoulda. or coulda, if a spacer fixes it, isn't that all you care about?

Rather than fix things, tightening everything up seemed to create problems. It's a guess, but the bike as purchased (well-used) was loose at the crank. After re-building the BB, the chain climbed over the big ring and also ground away at the big ring when on the small. My guess - and it's only a guess because I'm clearly not as smart as you - is that the LBS may have backed off on the tightening torques to compensate for a replacement spindle that was too short. I'm not sure. What I KNOW is that the fix was two-fold: (a) A 1 mm spacer at the fixed cup and (b) a 1.5 mm spacer between the chain rings. I did measure the width of the chain - 7.5 mm on the Schwinn vs. 7.2 mm on the somewhat older Nishiki.

Anyway, all is well now, apparently. I've only had it for short rides around my house but will take it out on a long ride - including a 1200 foot, 4 mile climb -tomorrow evening.

"Rpen," sorry if i was an annoyance. :-) To the rest of you, thanks again for your input. As always, I learned a lot.

rpenmanparker 03-09-14 06:50 PM

Quote:

Originally Posted by Duane Behrens (Post 16563482)
Rather than fix things, tightening everything up seemed to create problems. It's a guess, but the bike as purchased was loose at the crank. After re-building the BB, the chain climbed over the big ring and also ground away at the big ring when on the small. My guess - and it's only a guess because I'm clearly not as smart as you - is that the LBS may have backed off on the tightening torques to compensate for a replacement spindle that was too short. I'm not sure. What I KNOW is that the fix was two-fold: (a) A 1 mm spacer at the fixed cup and (b) a 1.5 mm spacer between the chain rings. I did measure the width of the chain - 7.5 mm on the Schwinn vs. 7.2 mm on the somewhat older Nishiki.

Anyway, all is well now, apparently. I've only had it for short rides around my house but will take it out on a long ride - including a 1200 foot, 4 mile climb -tomorrow evening.

"Rpen," sorry if i was an annoyance. :-) To the rest of you, thanks again for your input. As always, I learned a lot.

Excellent.


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