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Old 05-15-09, 12:29 PM   #1
DIYGUY
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Chain rubs against large chain ring

I am trying to solve a very puzzling problem - and need a little advice. The problem is that the chain brushes against the inside of the large chainring when it is riding on the small one - not much but enough so that when I have the bike in a stand and I spin the wheels slowly I can both hear it and watch it happen. This occurs when the chain is on smallest two of the freewheel cogs. It is the rivet heads that are contacting the inside surface of the large chainring.

Here is the setup for my bike:
1972 Peugeot PX10e
* Stronglight cranks 52/40
* Regina freewheel 14-17-20-24-28
* Regina chain 3/32"
* Shimano Deore XT RDR
* Shimano Deore XT FDR
* Normandy HF hubs

I have ridden and maintained this bike since it was new, so I know its history. For all of that I don't recall when, but sometime ago I crashed it and badly. The dropout flange to mount the RDR was bent as was the RDR cage. I have straightened both out fairly well. The axle is fine and I can spin the wheel in my hands and there is no wobble, bearing grinding or slop, nor any noticeable alignment issues.
I have just replaced several spokes that were kinked in the crash and trued and dished the wheel fairly well. the HF hub on the RH side has a distinct "out of true" spin to it, but it has no impact at all on the wheel spin, nor on the freewheel spin - mostly it is from having been pushed in slightly when I crashed. The chainline looks reasonably good to me.

I have tried to puzzle my way out of this and for the life of me cannot see why this is occuring. I ordered a new SRAM PC951 chain hoping that the smaller chain would solve this, and while it is on the way I am open to any and all insights here.

BTW - every part of this bike has just been torn down, cleaned, all bearings and races checked and repacked with new grease. This includes the BB, the hubs, the pedals and the head tube. The RDR has new pulleys as well. The axles were checked for straightness by rolling them on a bench stone and they are as new. So what is going on and what do I do?
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Old 05-15-09, 01:29 PM   #2
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did you put the chainring or BB axle on backwards?
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Old 05-15-09, 01:35 PM   #3
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"I have straightened both out fairly well."
check you rear drop out and dérailleur mounting with a park tools DAG.
then you can eliminated it if that is not the problem.
"This occurs when the chain is on smallest two of the freewheel cogs"
it also seems you are close to cross -chaining in this set up.
remember the old saying:
Patient:"Doctor! it hurts my arm when I move it like this...."
Doctor: "Then don't move your arm like that."

Last edited by cbchess; 05-15-09 at 01:39 PM.
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Old 05-15-09, 01:42 PM   #4
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Quote:
Originally Posted by DIYGUY View Post
.....the chain brushes against the inside of the large chainring when it is riding on the small one .....This occurs when the chain is on smallest two of the freewheel cogs...

What you have there is a classic case of cross chaining. The answer to the problem is don't use such extreme gear combinations.

The big ring should only be used for the first 3 of the smaller cogs in the back. The small ring on the front should only be used with the larger 3 cogs at the rear.

This will avoid the cross chaining issue. Although I have to admit that for a 10 speed you should be able to use 4 cogs per ring without issue. It may be that the bottom bracket spindle was swapped out at some point in the bike's history and replaced with the wrong length spindle. You can check this by laying a long straight edge along the inside of the big ring's face so the straight edge extends to the cogs in the rear. If the edge lines up pretty close with the gap between the middle and next out cog then your spindle is the right length.
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Old 05-15-09, 03:15 PM   #5
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Quote:
Originally Posted by AEO View Post
did you put the chainring or BB axle on backwards?
Thanks for the suggestion,
The BB was not removed - only the LH cup. The RH side was left alone, cleaned and lubed while in the bike. As for the spindle - it was easy to tell which way to insert it - the chainwheel side was quite a longer distance from the race to the end. I actually thought of that and checked to be sure. Dang it, this is a true tough nut to crack ...
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Old 05-15-09, 03:23 PM   #6
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Originally Posted by BCRider View Post
What you have there is a classic case of cross chaining. The answer to the problem is don't use such extreme gear combinations.

The big ring should only be used for the first 3 of the smaller cogs in the back. The small ring on the front should only be used with the larger 3 cogs at the rear.

This will avoid the cross chaining issue. Although I have to admit that for a 10 speed you should be able to use 4 cogs per ring without issue. It may be that the bottom bracket spindle was swapped out at some point in the bike's history and replaced with the wrong length spindle. You can check this by laying a long straight edge along the inside of the big ring's face so the straight edge extends to the cogs in the rear. If the edge lines up pretty close with the gap between the middle and next out cog then your spindle is the right length.
Thanks for the suggestion -
When the bike was new this was the setup that I had installed by the LBS. I rode this bike across the USA and have put many more miles on it since those days without this issue. Now that I am rebuilding it I have discovered it for the first time. I think it was caused either in the crash, or I have introduced it with my tear down and restore. Perhaps it was there all along and I was just DDB to it, but I doubt it. As for the spindle, it is original to the bike I am sure of that. But I may have done something stupid here so I will go over it again. And I will check with the straightedge shortly - good tip and my thanks ...
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Old 05-15-09, 03:27 PM   #7
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Quote:
Originally Posted by cbchess View Post
"I have straightened both out fairly well."
check you rear drop out and dérailleur mounting with a park tools DAG.
then you can eliminated it if that is not the problem.
"This occurs when the chain is on smallest two of the freewheel cogs"
it also seems you are close to cross -chaining in this set up.
remember the old saying:
Patient:"Doctor! it hurts my arm when I move it like this...."
Doctor: "Then don't move your arm like that."
Thank you!
I don't have such a tool critter in the kit. Is there some other way to check this that involves a little bit of old-fashioned engineering?? I can understand why this seems as if it is cross-chaining, but the thing never had this issue that I am aware of until I either caused it in the crash, or in my subsequent rebuilding.
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Old 05-15-09, 04:38 PM   #8
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Now just a minute here: You said it's doing this rubbing when it's on the smallest, outermost cogs on the cassette/freewheel in the rear, and the large ring on the front. Yes? If yes - that is not cross-chaining. If it were large cog on your cassette and large chainring up front - that would be cross-chaining. If you're getting rubbing in the small rear and the large front, the problem is something else.

Is your front-derailleur properly aligned with the chainrings? What I would do is re-install your front-derailleur. This is usually the easiest way to fix these problems. Rather than making adjustments after it's installed. Here are a couple good references - one written with illustrations, the second is a video:

http://www.parktool.com/repair/readhowto.asp?id=75

http://bicycletutor.com/adjust-front-derailer/

Good luck!
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Old 05-15-09, 09:32 PM   #9
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Now just a minute here: You said it's doing this rubbing when it's on the smallest, outermost cogs on the cassette/freewheel in the rear, and the large ring on the front. Yes?[/url]
No that's not what he said.
And the derailleur has nothing to do with the problem.

This is not an unusual problem. What concerns me is that apparently the rubbing started after the wreck or after the tear-down rebuild. This type of chain rub is a function of chainline and chain width, and the OP has already tried a narrower chain. So this leaves the chainline which must have changed after the wreck or rebuild.
Were the chainrings removed from the crankset spider. AEO's question was not fully answered. On earlier Shimano cranksets it is easy to get the inside ring reversed. As far as I know, all Shimano cranksets have the big ring facing outward to the right, and all other rings face toward the frame, to the left.
If the frame is straight a solution could be a 2 mm bottom bracket spacer to move the crankset outward 2mm. This is easily done on conventional bottom brackets and usually stops the rubbing.

Al
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Old 05-16-09, 01:04 AM   #10
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Rather confusing, but I defer. Here's a tech. doc. from Shimano showing what you should consider "normal" for the chain/FD rubbing. Don't blame me - I didn't write it:

(After doing a reinstall - my FD doesn't rub on anything/combination - Good Luck!)

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Old 05-16-09, 07:43 AM   #11
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Okay.... first of ..... DIYGUY should be able to use at least the largest 4, if not all of the cogs while in the 40. In the 52, all but the 28. It depends on how long the chainstays are. I use a 6 speed FW on a '83 Stumpjumper with 26/36/46 and I use all 6 gears in the middle without rub.

You say you crashed, badly. You need the frame alignment checked, the entire frame, front and back. Seek someone with a genuine alignment table, or a shop who has a system mastered that works for them. Someone who has the experience.

Another issue here, in my eyes is he's using the a XT FD where it doesn't belong. You need a double. Preferable and old school one with straight sides. Doubles have more clearance than triples. XT cages are always contoured for shifting performance on a triple, but don't offer the most room without needing adjustment.


Shimano diagrams ..... gotta love 'em . VERY general.
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Old 05-16-09, 01:42 PM   #12
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Read the OP's message. He clearly states that the chain is rubbing the side of the big ring while on the inner ring. This has nothing to do with the derailleur. This is a common problem, usually related to chainline.

Al
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Old 05-16-09, 03:56 PM   #13
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Read the OP's message. He clearly states that the chain is rubbing the side of the big ring while on the inner ring. This has nothing to do with the derailleur. This is a common problem, usually related to chainline.

Al
I gotta 'ya about the FD. His frame needs to be checked though. It's almost a given it's to be out to the left or right when crashed, hence affecting his chainline. A new chain won't help that! LOL
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Old 05-25-09, 03:00 PM   #14
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My sincere thanks to everyone who offered me their insights on this problem - I learned a lot.

I have been away for a week, and my new SRAM PC951 chain arrived. I put it on this AM and now the problem has been minimized. With the bike in a stand and moving the wheels slowly there is just a hint of the rubbing that I had with the original chain. Interestingly enough, when the chain has more tension on it (by spinning the cranks faster) the rubbing seems to be indiscernible. Oh and BTW - the back freewheel is now the SunTour Ultra 6-spd that I picked up. So I am satisfied and happy days! I now have a 12-spd with a good 5-6-7 inch jump between each.

If anyone has a suggestion on a source for a Stronglight 52T chainring (other than FleaBay) I am all ears. The one I have is just about worn to a nub ...
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Old 05-25-09, 03:13 PM   #15
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As I've found when R&Ring square taper cranks, their end position isn't as perfectly defined as the newer systems (ISIS, external bearing). A few times I have needed to adjust the front derailler because the position of the crank relative to the frame changed. Because the crank is sitting on a taper, the amount of torque applied and the friction between the crank and spindle at the time of installation can have a discernable affect on how far down the taper the crank slides. More than likely, when you reinstalled your crank, it slid further down the spindle changing your original chainline and causing the rubbing that previously did not exist.
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Old 05-25-09, 06:00 PM   #16
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Stronglight

http://xxcycle.com/chainrings-and-ki...glight,en.html
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Old 05-25-09, 06:07 PM   #17
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When you reinstalled and retorqued your square taper crank it now sits further inboard on the spindle. The hole enlarged just a little.
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Old 05-26-09, 07:01 AM   #18
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You know that thought occurred to me as well. I wondered if I could somehow shim the crank a little more outward, but then gave up on the thought. One thing I might try is to put a little aluminum flashing (as for example, sold by the BORGs) on one or two flats of the crankshaft, the idea being that the crank itself will not be able to pull down as far when it encounters the "shim." Has anything such as this ever worked for you?

Much thanks again ...
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Old 05-26-09, 07:33 AM   #19
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I wouldn't shim the crank taper. If anything, I'd tweak the adjustment of the bottom bracket cups a bit.
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Old 05-26-09, 07:36 AM   #20
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Me, I would just leave well enough alone. Each time you remove the arm you just might widen the hole a little more. Wait until the next time you have to take it off.

And I've never tried shimming, but I have used a longer spindle on an old crank.
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