I have a tandem which has a tensioner/idler pulley. I'd like to get rid of the tensioner, but the standard way of doing that on a tandem, using an eccentric BB, may be cost prohibitive with this frame.

I measured the BBs and they are exactly 25" apart (c-c). It seems like it's got to be possible using the right chainring sizes and possibly a halflink to get a chain that doesn't need a tensioner. Currently there are 40t chainrings on it and the chain has a lot of slack even when made as short as possible

it seems like exactly 140 links should be on the chain.. 50 running on each top and bottom (at 2 links per inch), and another 20 around each the chainrings. but as i said there is a lot of slack.. is there something i'm not taking into account? it's a brand new chain so no chain stretch

Your math is right, but the precision isn't.

A brand new chain is exactly 12" per 24 links, but with the least amount of wear the chain "stretches". Doesn't actually stretch like a rubber band, but wear at the pins allows the links to move apart slightly (think freight train stretching as it starts from a standstill). Likewise the chainrings wear radially so the wrap takes up slightly less chain than theory.

There's no way to reliably have a chain fit right and stay within tolerance for near zero slack, yet no tension without either an idler or an eccentric BB. If you totally object to having an idler, consider a Phil Centric BB in the forward position. (I put them forward because they're not cheap, and the forward BB has lower wear).

yes unfortunately all of the eccentric BB solutions that convert a standard english BB to a eccentric BB seem to use the modern hollow spindle, so I'd have to also buy a new crankset. The Phil BB alone costs more than I spent on the entire tandem, so at that price point i'd rather just save up for a better tandem or learn to deal with the minor issues of the idler. I've asked around about an american BMX BB (what i've got) to English eccentric BB but none seem to exist.

The main thing i dont like about the idler is the noise and the way it makes the chain feel like it's "indexed"/ratcheted.. the indexing feel isn't too bad, mostly noticeable when back pedaling. I reduced the noise by getting the chainline as perfect as possible, but it's still pretty loud. I'm hoping as the pulley wears down it will get a little quieter

You might try emailing these guys and see if they have an eccentric BB that will work.
https://www.precisiontandems.com/catframepart.htm

I had an old cheap tandem I played with as a project for the grandkids I used an old RD I had around for a chain tensioner it actually worked really good and since it was spring loaded it required no adjusting ever.
Here is a photo if it more on my webpage it you want to see.

Depending on your setup, you might be able to replace the pulley with one from TerraCycle: https://t-cycle.com/idlers-chain-mana...idlers-c-41_9/ . These are quite common on recumbents, and TerraCycle is the class of the field. Mine is perfectly quiet.

Your bike seems to have a 3 piece American BB (similar to a Thompson). One idea would be to switch over to a cartridge BB using an adapter and then use a BB attached Blackspire Stinger tensioner, which should be quite a bit quieter than your current system.



Either that or as Jeff Willis said get yourself a better tension pulley wheel.

There's a simpler way to do what you want. It's called a "ghost chain ring."

1. Make your timing chain as short as you can rejoin.
2. Find a chainring that will snugly fit between the upper and lower chainruns halfway between the cranksets.
3. Done.

The only hard part is finding a chainring that fits snugly.

having worked on a tandem eccentric last week, it seems that the OPs original idea my work. get the chain as tight as possible and there is a certain amount of slack permissable in tandems, perhaps 1/2 to 3/4 inch as it wears in.

i have never tried this, but i am able to pull the timing chain gears off my tandem when it is fully tight and then slide them back on. maybe if your timing chain slacks too much, use a half line for adjustment.

again: don't know if this would work, but would seem too.

How to convert an old freewheel into a robust, quiet idler. Does your solo bicycle freewheel make noise when you are pedaling? This won't either. I have built two of these, and they both work perfectly. https://sheldo

nbrown.com/idlers.html

In honor of this thread's reawakening after nearly 12 years . . . .