We've got about 800 miles on our Triplet, and I'm noticing that the timing chains that used to be snug are a beginning to slightly sag. Not causing any issues, but they are sagging a bit.

How long should we expect the timing chains to last? Any recommendations on replacement brand when it is time? What is a good way to test if the timing chain is still good/needs replacement?

(FWIW, the triplet is a cheap Micargi that I've replaced most of the junk parts on. It does not have adjustable eccentric bottom brackets, so I can't adjust the tension. The timing chains are original, which means the cheapest available Chinese chains.)

We've got about 400 training miles left, and then we'll be taking the Triplet on RAGBRAI (442miles over 7 days.) I want to make sure that it is either feasible the timing chains will last until 1800ish miles (the end of RAGBRAI) or I'd like to replace them before RAGBRAI begins. We don't want to be stuck in the middle of Iowa with a broken timing chain.

Have you measured the chain for wear? Seems more likely that the eccentric may have rotated slightly causing the sag in the chain.

Definitely check the eccentric. A timing chain should last a very long time, easily in the 5,000-10,000 mile range, since it doesn't flex or have to jump cogs or anything.
-Gene-

A sync chain wears just like any other chain, through mechanical wear of the bushingless pins that hold the links together... so chain elongation (aka, stretch) is checked the same way that it is for a drive chain. On your triplet, the rear sync chain connecting your two stoker's cranks will wear more quickly than the chain that connects your cranks to the middle stoker's, noting that each successive sync chain on a multiseat tandem will carry more load than the one ahead of it.

New sync chains will always show some early wear and sag a bit. In most cases you simply take it up with the eccentrics, adjusting the middle eccentric first and then the front one on a triplet: not sure what the Micargi uses to accomplish this.

Unlike a drive chain, you can basically run a sync chain on the same chain rings until the chain rings look like buzz-saw blades without much of a detremental effect. You can even double the life of your chain rings by flipping them around or rotating them 90* on the crank spiders at their half life when you throw on a new chain. Or, you can make a point of checking your chains for wear using a chain checker tool or a 12" ruler (do a Google search on "sheldon brown chain stretch") to preserve your timing rings. It all depends on how much wear and tear you put into your drive train as to how long they will last and, frankly, inexpensive chains last just as long as expensive ones on a direct drive like a tandem's sync chain.

My mountain bike took bag contains a quick link and chain tool that's part of my multi-tool.

Excuse my ignorance, but if you don't have eccentric bottom brackets, how did you install the chains without sag? I guess with help you could pull the chains tight enough to push a pin through with a chain tool?

Usually on an tandem sans-eccentric, a tensioner is used. It's kinda clunky, but effective.
-Gene-

But not, apparently, on the Micargi.

https://www.micargibicycles.com/produ...ail.asp?id=169

There was a previous thread in which the question was posed of just how this was handled, as there is no idler, but it appears there is not room for an eccentric in either of the front BBs. And it was left unresolved.

They came from the factory that way. I just assumed that when they need to be replaced that I'd ask you guys and you'd know

Oddly enough, the chain that is sagging most is the front timing chain, not the back. I'm wondering if the new chain ring I put on the new cranks is possibly part of the issue. (I switched to 175 cranks in front with Sugino XD600 cranks, and bought a 40T/110mm "BMX" chain ring for the timing chain.) I had assumed that all 40T/110mm chain rings were the same, except for weight and looks. Was that a safe assumption or is a "BMX" chain ring a bad choice for some reason?

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:
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.

Hey, wait, have you been stalking us? How could you possibly know that?
(In my head, when I look at the comparative chain sag of the two timing chains, I assume that it is a good measure of how much harder I am peddling than she is.)
So, we should be reasonably safe waiting to replace the chains until after RAGBRAI (<1800 miles)?

Decades ago we did the 'ghost chainring' thing as an experiment and it worked great.
Of course you'll get comments from other riders . . .
We were told once: 'But you can't do that . . .' Our reply "Yes, we know!'

Micargi saves $$ without eccentrics or tensioners and cheap components . . .
Another possible solution: replace 1/2 of each set of crossover chains with new chain; that would take up some of the chain stretch slack.
Pedal on!
Rudy and Kay/zonatandem

I'd have to see a photo of the bike as it sits today to see how much chain sag you've got to even hazard a guess.

However, that said... as already mentioned, if you can carry a pair of half links, perhaps a spare chain, etc., some re-useable chain links and a chain tool you'll have everything you need to keep you going so long as you're not worried about chain ring wear and tear.

So, I got out the digital calipers last night, and found that 6 full links (that should be 6.00") were 6.025", and using Sheldon Brown's rule of replace when the chain is stretched 1/16" in 12 links, that means I'm 80% to the point of needing a new timing chain. Even at this level of stretch, it isn't stretched enough to shrink it with a half-link. And, on our ride this morning, the bike threw the timing chain for no particular reason on a flat stretch of road.

Any recommendations on new timing chain brands? (Or sources to order them from?) Looks like its time to order one soon. FWIW, I'm more interested in cheap, solid and durable than low-weight, fast and pretty. OEM is 154 links and uses 40T sprockets.

I've had a similar weird timing chain experience on our triple this week. Just got back from a trip to Europe where we took our coupled triplet. Timing chains were tight when I disassembled for packing (I pulled the cranks for packing). I put it back together this weekend, and the rear-most timing chain is now noticeably slack. First, I swapped the two timing chains (which have the same amount of links and are same vintage/brand). Same deal. Then I thought the eccentric(s) must have moved somehow. But, I put an alignment mark on the eccentric and frame (using a Sharpie) before we first packed the bike, and they are still perfectly aligned.

It's easy enough to fix, I'll just adjust the eccentrics. But the *why/how* it happened escapes me. Any thoughts?

There are two schools of thought:

1) use the same chain as for your drive chain, so if anything breaks on your timing chain you can steal a link or two from the drive chain to replace it. And you only need on master link. This approach is a way to save a little hassle, but spend a little more money.
2) use any 6- or 7-speed chain, as they are stronger and more durable, and generally cheaper.

Given your interest in cheap, solid and durable. Go with 2). You should be able to go to your LBS, and combine two inexpensive chains to form the timing chain.

Also some shops stock big rolls of chain (I think KMC sells this way?) and can sell you just the length you need. Kind of rare, though. Maybe a tandem dealer might have access to this?

I did this, it worked great. I think I discovered the issues with why my timing chain died so fast: Our average speed jumped by 10%ish first ride with the new timing chain, and the chain is noticeably quieter than the old one. I'm guessing the old chain got some grit in it that I didn't realize and it just ate itself away while adding tons of friction to the drive line.

Live and learn. I didn't really notice any problems until I noticed that they were missing after the timing chain upgrade.

any opinions on dura ace cn 7801 chains being used for timing chain?

i have a bunch of extras for my regular road bike and planned on using 'em for the tandem (both drivetrain and timing).

A variant of #2 - just use a single speed chain, like SRAM PC-1. You can find these on sale for less than $15.

That what I'm using on the drive side currently and when I run out of 7700 chains for the timing side I plan on using the 7801 or 7900 chains.
My take on it is if it can handle the drive side where the power of 2 is being carried the timing side is only the captains power so not an issue.
I think this was mentioned last year on another thread.

That's what I do. Have to keep replacing drive-side chains, but the timing chain just keeps on going and going and ...