Broke the Timing Chain
 

First time we've done that. We were launching from a stop sign, seated, but I was maybe pushing a bit hard, and the chain just snapped. It's a Nashbar chain made for long-chain uses such as timing chains and recumbents. I think maybe I was trying to get too much use out of the chain, assuming that a timing chain would last over three drive chains. I checked my records to see when it was last replaced, and I was quite surprised to see that I had over 9,000 km on it (I usually replace the drive chain at between 3- and 4,000 km).

I would think that a timing chain would not get a great deal of stress due to its simple, direct run. But thinking about it, perhaps the strength differential between my stoker (female casual rider age 69) and me (male ex-racer age 59) may have had some effect. That, plus some chainline misalignment - the front timing ring (Shimano) sticks out a bit further than the rear (Sugino), but not noticeably. Still, there would be some bend to the timing chain.

I will have to rethink timing chain replacement, start getting serious and checking it with the measuring tool instead of waiting every n drive chains to replace.

L.

How did the chain actually break? Did a side plate separate from a rivet, did a side plate fail (split in half) at a rivet, or....???

I don't really know. It happened at a residential intersection with a 4-way stop, so traffic was fairly continuous at 6:30pm on a Friday evening. I spent a good five minutes hunched over like a fool on the corner looking for the broken link, but wasn't able to locate it. A side plate obviously came off because I had two inner links at the ends of the broken chain, but whether it was separation or failure can't be determined without the evidence!

Once I install a chain, I never remove it except to replace it. However, I did un-rivet this particular timing chain maybe 4500 km ago because the frame needed to be repaired (one of the tabs holding the bolts that tightens the eccentric was starting to crack), so re-riveting is pretty suspect. However, this is not a 9- or 10-spd chain, this is a cheap chain more in line with 5- or 6-spd use, so there's more tolerance for inexact riveting. That said, it's probably a good idea never to re-rivet a chain, as this always weakens the platess, or widens the hole for the rivet. Especially when there are connector link products out there that do a much faster and easier job.

The other alternative is to use a 1/8" track chain, which is not designed to bend sideways, works with 3/32 rings, and which comes with a master link that can be removed as often as you like. Except that we're likely looking at combining two chains with two master links.

L.

Is there anything wrong with doing that?

No. There isn't.

Chain wear is not a matter of mileage : how many watts does the team put on the chains, how well it is maintained, is the bike ridden in the rain, etc. The timing will have a longer wear then the back chain but there is no way to tell how much longer without measuring it.

One should always measure his chains and replace them when they are worn out. By doing so you make sure 1° the chain won't break, 2° it will work better : with wear, the fits less and less on the chainrings and cogs and wears them. This wear is caused by friction and this means degradation of the bike's riding qualities.

lhbernhardt, you are quite right to say it's bad to re-rivet a chain -- unless a quick-link (such as Sram's PowerLink) or a connecting pin (such as Shimano's) is used. Your 5-6 spd chain will not sit properly on your 8-9 spd chainrings -- I presume this is what your bike is equiped with).

The only time I've broken the timing chain was when I had it too tight.

Have broken maybe 4 timing chains in our 225,000+ miles of pedaling TWOgether.
Majority of the time stoker 'powered up' and got us home; another time it happened on a 5-day tour and chain broke in motel parking lot and had spare links/tool in our luggage..
However on my single (9-speed) utilized a chaintool and broke about 4 chains in a matter of months.
Never used to happen with 5 - 6- or 7 speed chains.
Get around 3 times the wear out of a crossover than drivechain on the tandem; but then we' are quite picky about keeping chains clean/waxed.
Pedal on!
Rudy and Kay/zonatandem

clearly need to upgrade to a belt.;)

The cost of the belt is more than his Kuwahara. Too much bling bling may cause it to pull to the left,

^ I was being faceteous.

There's also a bit of irony in my post, given that we broke the belt.

Hey, here's a side note to this whole timing chain thing: I was examining the wear on the timing chainrings (they were made for 5-6-7spd systems) and noticed that they were worn on the leading edge on the front timing chainring and on the trailing edge on the rear chainring. This clearly indicates that the pilote was doing most of the work most of the time!

This might be something fellow pilotes may want to check if you ever get any flack from your stokers! The wear on the rings will clearly show who does most of the work!

L.

I know, so was I.

And with that proof you will no longer have any issues with your stoker since you will not have one. Someone mentioned that the stoker is always right, maybe they are not but I am not the one to tell.

Does it? I am not sure. I think that would be the case even if the stoker did most of the work...

[QUOTE=lhbernhardt;10771655]Hey, here's a side note to this whole timing chain thing: I was examining the wear on the timing chainrings (they were made for 5-6-7spd systems) and noticed that they were worn on the leading edge on the front timing chainring and on the trailing edge on the rear chainring. This clearly indicates that the pilote was doing most of the work most of the time!

This is discussed by Sheldon Brown, who notes that this wear pattern in the timing chain
wheels is normal. If you think about where the CW under torque hits the chain it will be
obvious. This has the side effect that timing CW life can be extended by swapping the
stoker CW for the pilot CW now and then, of course best done perhaps at each drive
chain swap.