Solutions to a bad chain-line?

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,

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.

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!

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.