Tandem Cycling - Chain Hanging Up on Chain Ring Ramps

When I'm in the small chain ring the chain is rubbing against the ramps on the middle chainring. This happens regardless of which cassette cog I'm on. Sometimes the chain hangs up a bit and the rear derailleur arm pulls taunt.

I have recently installed a new middle chain ring and also have new wheels. The chain isn't new but shows little wear with a chain checking tool. I've double checked the installation of the middle chain ring.This problem may have been occurring before the change in parts but was not as noticeable. As a check I put another rear wheel with a different cassette on the bike and the problem is still there. There is a little play in the stoker bottom bracket when I grab the crank arms and try to move them side to side. (none in the captains crank arms)

This is a 2002 Co-Motion Supremo with Shimano Ultegra Octalink cranks. The bike has around 17,000 total miles. If I need to replace the rear bottom bracket, what size do I need?

Thanks

Something is definitely wrong. Can you take a photo that shows the chainrings in detail? Maybe from above, with the chain on the largest cog in the back?

Here's a photo. It's difficult to get the chainrings clearly.

So where is the chain making contact with the middle ring? Maybe you could turn it over to get a picture of the chainrings. It does look like the front is not centered on the freewheel, but that could be an illusion. But the chain should never have a chance of contacting the middle ring when it is on the granny and the largest rear cog.

Just looking at the photo, it appears as though there is a lot space between the big and middle chainring. Did you replace the middle chainring with the exact same brand/model of chainring or does it have a different off-set?

Looked at another way, is there an equal amount of space between the center of the big and the middle chainring as there is between the middle and small chainring, or is the gap bigger on the big/middle and smaller on the middle/small?

Figured out how to put my camera in Macro mode. Sorry the bike is a bit dirty, the roads were wet this morning.

The middle chain ring is an exact replacement for the Ultegra that came on the bike. The spacing appears equal between rings. This is a 9 speed setup with a 9 speed Dura-ace chain.

It's not hanging up on the middle chainring nuts--is it? THey appear to be hanging out a bit beyond the middle chainring instead of being flush.

The pictures are getting better! Now, get us a shot that shows the chain in the position you stated made contact: Small ring in front, large cog in back. And try to get a shot of the point of contact.

Did you replace the granny with a smaller one at any point? That middle ring looks funny to me; but I don't have an Ultegra triple; are they all like that?

The bottom line here is that the chain line I am wanting to see absolutely HAS to be neutral or away from the middle ring, so no way could it hang up on the middle ring unless something is really majorly wrong.

If I need to replace the rear bottom bracket, what size do I need?

Shimano BB-6500, 118.5mm spindle and with 17,000 miles that might not be a bad idea even if it's not the root cause of your chain ring interference.

That middle ring looks funny to me; but I don't have an Ultegra triple; are they all like that?

Yes, that's what they look like...

This is a 9 speed setup with a 9 speed Dura-ace chain.

I'm stumped...

Agree with TandemGeek on replacing the bottom bracket - especially if you can feel the play.

Another thing you may want to check is the small chain ring. Could it be possible that what you're getting is not rub on the middle chain ring but actually chain suck? Different combinations of "stetched" chains and worn chain rings can cause issues. A burr on the small chain ring could also cause issues. I've seen the chain rub on the chain rings in extreme cross-over situations but not "regardless of which cassette cog" you're on.

I believe I've found the problem. The small chain ring appears to be bent slightly. I'm going to replace it along with the bottom bracket.

Thanks for the help.