# Timing Chain replacement



## ds2199 (Sep 16, 2008)

Does anyone keep track of how many miles they get out of a timing chain? 

Do your replace your timing chain at any particular frequency?

Do you use the same chain as drive side? 

This seems to make the most sense from a compatibility standpoint. Not sure if the longevity makes a difference to use an 8sp or single speed chain on for timing.

I'm just curious while doing some winter maintenance and realized that I have never changed the timing chain on our ECDM 29. I'll have to see how a new chain might work on those rings...


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## Okayfine (Sep 7, 2010)

I don't keep track, but it's an every-couple-years kind of thing - I measure pin-to-pin over 12 inches and change when there's a 32nd, and it's still a years' replacement schedule. I use 8-sp chains. Thinking about it, I'm not even sure when I last had to adjust tension for the sync chain...


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## switchbacktrog (May 10, 2013)

I seem to get about 300 miles from a normal 9 speed chain and 1000 miles from a KMC X1 singlespeed.KMC CHAINS Tandem Crossover Chain Nickel Plated 160 Link KMC X1 - £40.00 - Components - Chains & Spares - JD Tandems.

This is to 0.75% "stretch" on a chain checker.


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## ki5ka (Dec 17, 2006)

Wow, that's interesting data, quite a difference! We have about 500 miles on the 8 speed chain I have on now. Since putting on the wide-narrow chainrings, never had a skip or drop. As best I can remember, have only adjusted tension once.


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## TandemBear (Aug 18, 2013)

ds2199 said:


> Does anyone keep track of how many miles they get out of a timing chain?
> 
> Do your replace your timing chain at any particular frequency?
> 
> ...


I don't keep track of miles, but I was surprised to find my mtn. timing chain wore out WAY before the drive chain. Strange I thought because only half the power is being transferred through the timing chain, whereas the drive train has twice the power acting on it.

I happened to meet a Dumond Tech guy at Interbike one year and I brought this issue up. He agreed that they'd seen the same thing - timing chains wear FASTER. How on earth could that be the case?

He surmised that since the timing chain's going through the same radius arc every single time around that the rollers are being worn in the exact same place every time. A drive chain goes through rings and cogs of varying size, plus the tiny derailleur pulleys, so the chain's constantly being rotated different amounts with each revolution through the drivetrain.

Makes sense to me.

That said, I really need to look at my road tandem chains. They're original Sedis Silver chains that have lasted forever. But no chain lasts forever!!!


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## ki5ka (Dec 17, 2006)

Thing is, the timing chain doesn't have to shift, so I'm inclined to think that if it isn't slipping teeth, no reason to sweat it.


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## ds2199 (Sep 16, 2008)

ki5ka said:


> Thing is, the timing chain doesn't have to shift, so I'm inclined to think that if it isn't slipping teeth, no reason to sweat it.


That is kind of my thinking. I tend to neglect it. But by the time I get around to doing something, I may need to get new rings in addition to the chains. I think I have 3000 miles on my timing chain/rings now. I just checked it and it and the park chain checker would say it is nearly 100% worn out.

Can you put a new chain on without replacing the rings if it is worn this much?


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## Okayfine (Sep 7, 2010)

If you haven't swapped the timing rings, you can get another life out of them by swapping them front to rear. On worn sets, you should be able to see the worn face on the front ring is opposite from the worn face on the rear ring. 

Now, whether the wear you have is to the point that a new chain won't mesh, I dunno. But I did the swap on our last set of Middleburn rings and had no issues.


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## Iowagriz (Jan 14, 2008)

Just back into tandems after 15yrs out. How do you measure the timing chain tension? Is this part of the equation on why some are wearing out faster than others? I think that I remember that you want about 1/4 to 3/8" deflection when moved by hand. Wouldn't too tight cause premature wear?


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## TandemBear (Aug 18, 2013)

No, timing chain tension probably wouldn't be the culprit, unless it were extraordinarily high. Timing chain tension is low compared to tensions created under pedaling loads. And then think of the drive chain - it's seeing twice the force input at the pedals, so it's under even higher tension. And as we've been discussing, timing chains seem to wear faster then main chains (even though they're longer and distribute wear through a longer chain run per tire revolution as well).

I've noticed that when I load the front pedals with the rear wheel locked, the lower chain tension drops significantly; as in I see the chain slack as I load the pedals. So to reduce the chance of errantly dropping a chain due to chain slack in the bottom, I brought my timing chain tension up a little bit more.


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