[teachndad]

Hi,

I recently bought a used inexpensive-brand tandem with a missing idler pulley. The pulley sits on a mount halfway between the two front cranksets. I now have a pulley, but now the question is: How much tension should there be in the chain? I assume you check the tension with the chain length running on the top of the chain loop from the Captains crankset(not sure if terminology is correct) to the stoker crankset. There is currently @1/2" available movement in the chain when I pull it up.

Thanks.

Rod Wylie

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[TandemGeek]

The sync chain that connects the front (captain) and rear (stoker) timing ring / cranks should have about .5" to .75" of slack on a tandem that uses an adjustable eccentric bottom bracket for the captain's crankset. Chain tension needs to be checked throughout the entire rotation of the cranks to ensure that any non-concentric timing ring orientation that could create highly unequal chain tension is discovered and minimized by loosening and recentering the timing rings on the crank spiders.

For a tandem that uses fixed, non-adjustable bottom brackets and a fixed idler wheel, not more than .5" of chain tension is more appropriate to ensure the chain can't jump off the idler wheel when the tandem travels over rough pavement or terrain. The idler wheel's position should also be periodically checked to ensure it that remains in line with the front & rear timing rings. If the idler arm gets bumped and knocked out of plumb from the timing rings chain drops become more likely.