Chain ring orientation?
 

We have had our Trek T1000 tandem for about 2 years now, and it has never shifted properly in and out of the granny ring. We only need this on very steep hills when we're tired, and the chain invariably does one of several things: 1)falls off towards the inside, 2)jams between the granny and the middle gear and gets stuck. I came to the conclusion that the chain rings were never installed correctly, so I started trying different permutations and combinations of chainring orientations:

Original, chain tended to jam between chain rings:

http://bikeforums.net/attachment.php...hmentid=262767

Flipped granny ring around, now chain would suck and jam underneath:

http://bikeforums.net/attachment.php...hmentid=262768

Finally, flipped middle chain ring, and this seems to work, at least on the stand. We'll see when the chain has 600 lbs of tension on it....:

http://bikeforums.net/attachment.php...hmentid=262769

This configuration only works if I install the N-Gear Jump Stop. Otherwise, the chain invariable falls off and jams on the between the granny and the frame. Also, without the chain deflector installed, it is literally impossible for the granny to catch the chain as it shifts down because the angle of the chain is such that it will miss the teeth.

In all of these configurations, the rear derailleur is set to the largest cog.

Is this normal? Are the chain rings in the correct orientation? I'm at a loss here if this latest configuration does not work. We are going out tomorrow to test it.

Thanks for your opinions.

Changing the number of teeth on your ring(s) can cause problems as the shifting ramps/notches are positioned for certain 34X50, 36X50, 42X52, 39X53. etc. if you chnage one you have to get it to match the other size, and change the other size so the ramps match the new replacement. The chanrings need to be oriented to the crankarms rotationallly in a specific way, in most case a protrusion on the inside of the ringm will need to be aligned with the crankarm. Some inner rings have a slight offset to the teeth some don't, changing ring offsets can cause problems as well. For a chain that drops off, sometimes the only "fix" is a "chain keeper", ther are several designs see- http://www.amazon.com/Redline-Cyclo-...e+chain+keeper for simple and cheap option- most shops stock at least one type

The middle ring is most likely countersunk for the chainring nuts which will indicate which way it is intended to be flipped. But just based on the appearance of the pins and profiled teeth on the middle ring, I think you now have it flipped incorrectly.

The inner ring is probably not countersunk. But usually any markings on the granny should face inward.

As far as rotational orientation, there is usually some indicator (perhaps a small triangle stamped into the ring or a tab sticking out on the inside of the ring) to show intended alignment with the crankarm.

Don't shift from the biggest cog. In fact, you probably shouldn't use the biggest cog with the middle ring as the chain deflection is extreme. I recommend performing downshifts to the inner ring from the 3rd largest cog (or smalller). If you're riding the middle ring on the 2nd largest cog, first upshift momentarily to the 3rd largest cog before downshifting to the inner ring.

"We'll see when the chain has 600 lbs of tension on it....:"

You should relieve most of the load on the chain while you are shifting; shifting under a heavy load is hard on the chian and makes for difficult shifts. Ease off the pedal pressure while shifting, shift down early before you get to that big hill.

+1 on the Jump Stop, I install one on my bikes as cheap insurance against dropping the chain.

This is a symptom of a worn-out chainring.
I recently put a new chain on my touring bike. Immediately the middle ring would do this all the time, jamming the chain into the FD. The small ring would make noises as it tried to do it but wasn't quite able to hang on. Replacing the rings eliminated the problem.

Since you have the Braze on band for the FD, a K edge chain catching stop will work,
It uses the bolt that mounts the FD ..

I like the wear of Surly's Stainless steel chainrings, but they are not ramped.
they are flat , and can be flipped over..

Thanks for all of the suggestions. We went out this morning with the latest configuration, and it worked great, the shifts from the front were smoother than I've ever experienced. I still don't know why the cranks were assembled the way they were, but the addition of the chain deflector made all of the difference. Now I need to get a new chain, as some of the links on the existing chain are bent from being jammed so many times.

Thanks...