Originally Posted by
SvdSinner
Oddly enough, the chain that is sagging most is the front timing chain, not the back.
Ever hear the expression, "She's not pedalling?" Seriously, it's hard to know exactly why one chain may have more sag than the other: lots of variables at play. But, if your stokers aren't putting forth at least enough effort to pull their own weight, the captain can find they're pushing their stoker's feet. Tat puts more load on the front sync chain than you'd normally get with stokers who have an efficient pedal stroke and contribute to the total power transmitted by the second sync chain that connects to the rear crank axle.
As for your original question, how to deal with chain slack on THIS bike, there are a couple options.
1. Just let the chains do their thing and when they have stretched by 1/8" measured with a chain check or ruler (see link in previous post), just make-up replacement sync chains using the exact same number of links as the original ones. Replacing them requires pulling one crank for each sync chain (
i.e., the captain's and the rear-most are the easiet on a triplet) and then manually re-aligning the crank arm phasing just as you did when you changed out the front cranks. No big deal. You'll get a couple thousand miles out of the chains this way without damaging the rings.
2. You can also use the run them until they're worn-out approach to the sync chain and timing rings. To take up the slack in the chain you can do one of two things:
a. You can buy a 1/2 link and use it to replace a full-link to take up 1/2" of slack, or wait until the chain has stretched enough to allow you to remove a full link. You can do this until the chain ring teeth look like saw blades and then get four new rings and new chains; begin again.
b. You can install a 'ghost ring' in the sync chain to take up the slack (
see photo below, which shows a tandem with a ghost ring... as well as out-of-phase cranks and what appears to be an unusual kiddie crank installation). A ghost ring is a chain ring that has a few more teeth than your timing rings that just 'floats" there as a tension adjuster. As your chains wear you stick in a larger ring to take up the slack. Again, like removing links, you can do this until the timing rings need to be replaced.
There are a number of variations in between that can extend the life of your timing rings as well. Again, as noted in an earlier post, you usually flip your chain rings around on the spiders which effectively restores your timing rings to the original pitch so that a new chain can be installed, but to make this work you must make that decision before they've been completely worn out on the opposite side.