Bicycle Mechanics - upgrading an older Schwinn tandem

I'm trying to upgrade an older Schwinn tandem that I found in very good condition but with not so great components. I'm presently occupied with installing new cranks, replacing the old, steel cottered cranks. I've successfully swapped out the stoker cranks, but the captain's is proving to be problematical. It has a cast aluminum eccentric that fits into the front b/b hanger, secured by two pinch bolts on the bottom of the shell. The shell is 73 mm wide. The eccentric fits flush on the left side, but protrudes 5 mm on the right side to provide a tab with which to rotate the eccentric for adjusting timing chain tension. I've tried fitting a 73x122 mtb cartridge b/b, but the extra 5 mm on the right side of the eccentric moves the spindle too far to the right. Does anybody have a suggestion as to how to deal with this...?
Thanx!

I'm trying to upgrade an older Schwinn tandem that I found in very good condition but with not so great components. I'm presently occupied with installing new cranks, replacing the old, steel cottered cranks. I've successfully swapped out the stoker cranks, but the captain's is proving to be problematical. It has a cast aluminum eccentric that fits into the front b/b hanger, secured by two pinch bolts on the bottom of the shell. The shell is 73 mm wide. The eccentric fits flush on the left side, but protrudes 5 mm on the right side to provide a tab with which to rotate the eccentric for adjusting timing chain tension. I've tried fitting a 73x122 mtb cartridge b/b, but the extra 5 mm on the right side of the eccentric moves the spindle too far to the right. Does anybody have a suggestion as to how to deal with this...?
Thanx!

How very strange. Could you post pictures?

If it's from the era of cottered cranks, then I suspect it will accept English threaded 68mm width bottom brackets without a problem. That would allow you to use any width BB you require.

I too would like to see pics. with all due respect Prof Honeydew, if the BB shell is 73 the OP needs a 73mm bottom bracket like a older MTB may have. I suspect the issue is that it inserts from the rightside and therefore the flang rest a bit too fat to the left.

is this it? can you flip the eccentric over so the adjuster is.... OH sorry that wont work then your spindle will be backwards PICS!!

Have you pulled the eccentric out of the frame? the more common use of setscrews means they make divots,

the divots may make it hard to shift over ..

Get a Phil wood BB they are adjustable in 2 ways,
lock rings are able to be tightened in a bit of lateral adjustments,
and the Axle can be pressed thru the bearings
to shift it sideways too..

The cast aluminum eccentric slides in from the right side----a raised lip bears 'gainst the hanger. The fixed cup screws in 'gainst the lip, which positions it 5 mm from the frame. I'll take some snaps and post 'em. That should help illustrate my quandry. Right now I'm thinking along the lines of replacing the orig. eccentric with a Phil eccentrik, assuming I can get one for the 73 mm wide shell.

I too would like to see pics. with all due respect Prof Honeydew, if the BB shell is 73 the OP needs a 73mm bottom bracket like a older MTB may have. I suspect the issue is that it inserts from the rightside and therefore the flang rest a bit too fat to the left.

is this it? can you flip the eccentric over so the adjuster is.... OH sorry that wont work then your spindle will be backwards PICS!!

I've seen Schwinn tandems with cottered cranks- they were all from the '50's, possibly the '60's. If this is so, they'd predate the MTB 73mm width bottom bracket by 25-ish years.

At least I'm pretty sure- it's a rare beast in any case.

Found the solution to this prob in my parts bin. A PHil Woods b/b. The lock rings allow me to shift the spindle leftward in the eccentric to where it's centered on the frame. Simple!




I'm trying to upgrade an older Schwinn tandem that I found in very good condition but with not so great components. I'm presently occupied with installing new cranks, replacing the old, steel cottered cranks. I've successfully swapped out the stoker cranks, but the captain's is proving to be problematical. It has a cast aluminum eccentric that fits into the front b/b hanger, secured by two pinch bolts on the bottom of the shell. The shell is 73 mm wide. The eccentric fits flush on the left side, but protrudes 5 mm on the right side to provide a tab with which to rotate the eccentric for adjusting timing chain tension. I've tried fitting a 73x122 mtb cartridge b/b, but the extra 5 mm on the right side of the eccentric moves the spindle too far to the right. Does anybody have a suggestion as to how to deal with this...?
Thanx!