Tandem Cycling - loose chain on tandem?

Hello experts,

I am new to tandeming, and just got my used burley duet back from the shop where the front end was fitted to me. it seems like the chain which connects the two cranks (timing chain?) has more sag in it than it used to. what's normal, and how is it adjusted?
i am very psyched for a summer of two-up riding, and am taking my 9 yr old on the GOBA in Ohio.

thanks in advance,

Pat

It is an eccentric on the captain's bb. If the chain can come off, it is too lose. Guideline is half-inch vertical deflection at mid-span.

Thanks for the prompt reply. so the bb rotates and is tightened it looks like by a set-screw? i wonder how it loosened while my front end was being adjusted...

This previous posting contains a collection of links to other posts I've made that discuss the eccentric and timing chains: http://www.bikeforums.net/showpost.php?p=1790025&postcount=31

You'd need to ask the shop what they did to your eccentric and why, as there could be a number of different answers.

thanks, maybe i'll keep an eye on it this weekend.

As noted above, if you've got more than about 1/2 inch play in the middle of the chain rings it probably should be adjusted, but because the spider arms on your cranks may not be perfectly centered, the chain slack may be different at different pedal positions.

If you need to adjust the eccentric bottom bracket, the easiest way to do it is with a Park Tool Pin Spanner (the green one). It slips into the two pinholes on the side of the eccentric and gives you a nice handle to rotate it. You will need to loosen both set screws and gently rotate the eccentric until the chain is at the proper tension, then re-tighten the two set screws. While you have the set screws loose, be careful that you don't push the entire bottom bracket off center as it will just be sitting in it's tube at that point.

After you've got it tightened back down, check the tension with the pedals in several positions. If it varies, you may need to center the crank arms...there are instructions out on Sheldon Brown's website and probably at TheTandemLink.com for doing that.

Don't over tighten the chain tension. If you do, it will cause drag (and probably excessive wear and tear) as you pedal. If you remove the rear chain so the cranks rotate freely, you can easily tell the difference between a timing chain that is properly adjusted versus one that is too tight.

Good luck and happy riding.

Do you need to have two pin tools to adjust the eccentric or will one do the job?

David

Do you need to have two pin tools to adjust the eccentric or will one do the job?

David

Hey David, I think we have about the same bike: After loosening the two allen bolts under the eccentric, I've always been able to make the adjustments with my hands...I'm not exceptionally strong, or anything, so you should be able to do the same.

To answer your question, you would only need one pin spanner (with two prongs) to make the adjustment, if you were using a pin spanner.

Do you need to have two pin tools to adjust the eccentric or will one do the job?

One is all you need (Green/SPA-1, Red/SPA-2 Park Pin Spanners or similar from others will work), if even that. If the eccentric is well-maintained... which is to say that you take it out of the shell, clean, and lubricate it at least once a year which is also a good idea for bottom brackets and headsets ... you can often times rotate them with your fingers.

Anecdotal maintenance tidbit: We have some friends who went to replace a 10 year old rear bottom bracket (UN72) installed in a steel frame. No luck, so it went to a shop where they worked on it for two days before giving up for fear they'd do some permanent damage to the frame. It will most likely go back to the frame builder who will have the tools needed to hopefully extract the old cups and then chase the threads so that it can accept a new BB.

So yesterday i rode to my baby-momma house to pick up my daughter (stoker), and heard some creaking under foot. the eccentric was so lose it was sliding out the starboard side of the bike! obviously, i didn't need a pin wrench, just rotated it by hand and retightened the set-screws. i bet the shop adjusted the chain, and forgot to retighten the screws. the lil stoker and i found that 15-18mph is a great pace for the two of us. the bike is certainly unwieldy with an empty back seat. while riding solo, i told a little kid at a stoplight that i was riding with a ghost (see, he's pedaling back there!).