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Solutions to a bad chain-line?

7408 Views 20 Replies 8 Participants Last post by  redmr2_man
08 Ironhorse MkIII, upgraded the rear wheel/hub/cassette/chain and came into this problem about six? months ago. Hasn't been an issue at all until now. I'm starting to wrench more and more on my own (or messing stuff up worse and having cool buddies fix it for beer :thumbsup: ) and wanted to know how I can fix this?

My photography isn't the greatest, so bear with me and hopefull these work well to show the problem:

Now my issue is that while grinding up hills in 32t(middle ring)-34t(largest cog on rear cassette), my chain slips off my front ring and drops into 22t-small ring, or between the two. Happened like 25x today! :madman:

-There are no crank spacers on the driveside.
-This issue wasn't here before new hub/wheel/sram 990cass/chain.
-32t front ring isn't bent.

It seems quite obvious, to me at least, that this is purely caused by the bad chainline as seen in the pix above. Seems on slower grinds up a hill at slow cadence, the chain would come into the front rings at an angle to pull it down to the smallest ring. Am I right?

How can I make that chainline straighter, preferably without the use of a tensioner/pulley add on to the cranks. Do they make spacers for the hope pro2 rear hub / 990 cassette to "push" the cassette out further, thus making the chainline straight? Can I tune the derailluer around this whole problem? Any other options?

Help a noob climb some hills, and thanks in advance! :)
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either swap cranks or shift to the 22 ring. outboard cranks ahve 49-51mm chain line. the best you will find in a modern crank is around 47.5 or so
Looking at the picture (and putting a sheet of paper on my screen as a gauge) it appears that your chainline isn't so far out of whack. Ideally your middle chain ring should line up with the middle of the cassette, and yours appears fairly close. Check by putting a straight edge against the chainring on a tangent and carry the line back to the cassette. Allow for the distance from the chainring face to the centerline and see if it comes close.

Now to fixing your problem which is probably caused by chain and chainring wear.

Before starting, check the chain for wear, aka stretch, (do a search here for chain stretch if you need more info on this) as there's no sense wasting time if you need a new chain. If you do replace the chain look for a chain with the inner plates flared outward in the middle creating a wider bellmouth or funnel to pick up the points of the teeth and guide them in.

Now to the chainring. With wear the teeth get thinner, and the points get blunted or chipped, causing them to have more difficulty gliding into the chain when it feeds from an angle. You can improving angular pickup with a file.

Since your chain is falling to the inside you want to move the points of the teeth inboard a bit, so hold the file at a shallow angle and rotate the crank to file more angle on the outside of the teeth. Note, you don't want to blunt the teeth, so keep the file angled as you would to sharpen a knife. Do this by degrees checking for improvement as you go along, and don't get carried away. later, you can do the same with the granny if needed.

Good luck,
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Everything FBinNY said, and just a quick note...

It's almost impossible to cause a chainline problem with a rear wheel switch. There might be a few 10ths of a millimeter different in position of one cassette to the next as various wheels are put in place, but rear chainline is more-or-less governed by rear dropout spacing. Any reputable hub -- and probably most crappy hubs -- are going to fall in line with the middle cog in the 47.5mm position.
Alright sweet, I'll check the chain out tmrw, could definitely be the cause!

Thanks for all the info.

sidenote: This all happened upon first putting on the new wheel/hub/etc with no miles on the drivetrain, but went away or was fixed by ppl messing with my bike.
Yo Red!

You presented this as a chainline issue, so we dealt with it that way. While I don't think it's chainline, there's the possibility that it's only a simple FD trim adjustment problem. Check that the FD is correctly adjusted and the cage is parallel with the chainrings.

There's an equally good chance that the FD isn't the cause, but it's always good practice to check and eliminate the simplest things first, before spending time and money replacing parts.
Ok so I checked the chain last night (finally) and the chain is good. The 32t ring doesn't look bent at all...and no shark teeth so it's looking pretty good as well.

The front D isn't touching the chain at all in that gear combo, not even a that can't be the case.

I'm lost at what to do here..
redmr2_man said:
The front D isn't touching the chain at all in that gear combo, not even a that can't be the case.
Is the inside plate of the front derailleur close enough to the chain to prevent it from dropping down? This a crapshoot suggestion, becauise in theory nothing at this end has changed. But it may be worth your time to reset your front derailleur, ensuring that your inside plate is a gnat's ass off the chain when you're in the 22x34 combo, with the cable unattached.
After changing the chain/cassette I had the same issue, ended up being the chainring was worn. Replaced it and everything is good.
Now that we've eliminated the easy stuff, you need to watch carefully and see exactly what's happening. The chainring should accept the chain from any sprocket on the cassette without the chain running off the side, or needing the FD to help keep it on. (this is what makes 1x9 possible)

Trim the FD so it's well centered and turn the crank slowly with the chain coming from the innermost sprocket (the worst case). Watch from the top so you can look through the chain and see the tips of the teeth engage. You'll probably see that they're hitting on the inner plates rather than slipping nicely between them. It may happen only on the first tooth after the shift gates, (cut-down teeth) or it may be random.

If that's the case, you've found the problem, and the solutions are some or all of the following:

1- use better chain lube, to keep the chain as supple as possible and help the tip of the tooth slide down into the plate without lifting the chain

2-Use a chain with more bellmouth in the middle of the inner plates. This acts like a funnel and improves angular pickup.

3-Replace the ring, possibly with one having no shift gates. (if they're the problem)

4-Use a file to move the points of the teeth, or one tooth after the gate, in the direction that the chain is coming from. Imagine that the following slashes are the tip of the chainring teeth in profile -- /\ -- if you file at a shallow angle on the left side of the point you'll move the point to the right slightly. Since the sides of the teeth keep the chain in place moving the point slightly will help it slide in rather than hitting the edge of the plate.

If you go the filing route, do it by degrees, and check often so you do only as much as necessary.

BTW- there are some who frown on things like filing chainrings, but those who were wrenching back in the Bronze Age, will tell you that chains staying on were the exception and falling off the norm, unless this kind of work was done.
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I'll try trimming the front D a bit next time im in the garage. The chainring is a truvativ and it's pretty new (6mo./under a 1000 mi). It doesn't appear to be bent in any way, but slow circling the cranks around, it does "catch" and "uncatch" the chain in a few spots, but not enough w/o load to drop the chain with it in the stand.

I would not like to file the chainrings, but thanks for the suggestion.

1-I use prolink chainlube, and the chain feels supple and oiled. Should I try something else, if so, what're your thoughts?

2-This is a sram 990/1? chain, what are your suggestions for a chain that might be better? Any downsides to a chain with a wider bellmouth?

3-Thinking I'll try this route first after trimming the front-D. In the past I tried a shimano xt ring, a raceface ring, and a blackburn rings, and neither would work right (all were 10432's). They would cause the chain to skip down between 44t big ring and 32t middle ring no matter what was done to the front D. I'm chalkin it upto a weird truvativ crankset *(firex), as this problem went away with a truvativ ring. I'd love to be able to use an XT ring, heard they're way stronger!

4-won't be doing this, but thanks!

FBinNY, I think I've seen your helpful posts on RBR as well. Thanks for taking the time to be thorough and helping me out. It's appreciated!
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Now that you see the catching, you know what's happening and the cause.

You can trim the FD, using it to help keep the chain from going totally off when it catches. This is what some of the devices that 1x9 riders use are about. I'm not a fan of this approach, which to me is putting a bandaid on the problem rather than actually fixing it.

Don't ask me which chain oil I think might help, you should know what my answer to that question would be. But, a better chain oil would only help marginally, mitigating the problem by reducing the frequency of the chain falling off, but not actually solving it.

Replacing the ring is your best bet for actually solving the problem, but isn't a guaranty.

What I don't understand is why you won't consider the file. This goes to the heart of the problem and is most likely to solve it, and at the lowest cost. If you're willing to replace the ring anyway, you have nothing to lose by trying the file solution first. It isn't difficult, won't cost you a dime, and you'll have the satisfaction of actually fixing something rather than simply spending money.

If you're not comfortable with your own hand skills, look for an experienced mechanic. One who has been around at least 20 years. Print my prior post and ask if he'll try it. Odds are he's already familiar with this procedure, but if not he'll understand what needs to be done, and save you some dough.
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I've actually tried the file method to remedy a very similar problem.
I had never heard of anybody else doing this at that time, but it seemed like the logical thing to do to troubleshoot the problem.
Since the first time i did it about a year ago, I have done it to a few more setups and it really helped.
I often will file down the shifting ramps on some setups.
Like on some 10 speed road setups with a triple up front.
Alot of times if you are in middle front, small back, if the chainline isn't perfect and can't be changed for whatever reason, the chain will catch on the shifting ramps or pins and cause some serious issues. Filing fixes these issues almost everytime.
On some older shimano chainrings, I don't see how they would work without some sort of filing.
I'd give it a shot as Francis suggested.
Truvativ shift pins can really screw stuff up if they are jarred loose from bad shifting. Sometimes they get nicked and need some smoothing.
Honestly because it just sounds easier to replace the ring. They aren't too expensive, and time is money my friend!


I DO appreciate the tips though.
put your old cassette on the new wheel.
redmr2_man said:
Honestly because it just sounds easier to replace the ring. They aren't too expensive, and time is money my friend!


I DO appreciate the tips though.
Makes sense. Time is money. If the price of a new chainring is worth less than 2 minutes of your time, go for it. But I'd venture that it takes more time to replace a chainring, than to re-camber the existing one. If you were in NY I'd offer to race.
Without having read all the above responses, I don't see this as being a chainline issue, but more an issue of the new chain not playing nicely with the old chaining. I would try a new ring. Even if it is not bent, it could just be worn in a way that makes it not work well with a new chain. It could possibly be the chain itself, but I am kind of doubtful that it is.

This may be way off base, but did this problem at all coincide with replacing the rear triangle?
kapusta said: issue of the new chain...
Oh, jeez, how did I miss that little tidbit of info?

Yep, good bet.
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