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Broke old but lightly used chain: what to do?

Old 09-11-12, 07:09 AM
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Broke old but lightly used chain: what to do?

I am a novice, but getting a crash course. Have done a bunch of reading in the last couple days. Your help would be appreciated.

Started riding my ~30 year old, 10sp, mountain bike in lieu of running till an injury healed. Bike manufacture unknown, as I stripped and painted it as a kid. Busted the chain and not certain what to do. Measured stretch of no more than 1/32” over 10”, so I would guess this chain is still GTG if I can put it back together “properly”. I believe this is the original chain on Shimano cogs and SunTour derailers. It is a bushing-type chain. Width of pins is 7.8mm. Width between inner links is 2.5mm. There are markings on some of the chain outer links, but not all: “W S”, “TAIWAN”, and “4-3” on a single link. There is a single “master link” on the chain already, one side only. LBS sold me a clip-type master link to repair this chain, but it is too wide for the rear derailer, if not the cog spacing.

Some posters indicated in threads I read these older chains suffer little weakening by reusing pins and links. Should I straighten the bent outer links and simply reassemble? Purchase a proper “master link”/PowerLink/Missing Link/etc? If so, not certain which one. Advice? Thanks.



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Old 09-11-12, 07:51 AM
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Chains are disposable items. Why risk another failure when a new chain would work?
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Old 09-11-12, 07:59 AM
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This type of chain can be respliced with a chain tool, and reused. But you have to address the cause of breakage, which is possibly the result of a bad splice, but more likely because of aggressive shifting under load. When you shift under load the chain is flexed sideways as it tries to engage the new sprocket before coming off the old one. This pries the plates apart, moving them to and eventually beyond the ends of the pins. Once a plate is hanging half off the end of a pin, all it takes is aded tension, like when you climb a hill to have it fall off and the chain to snap.

Before reusing the chain examine it carefully for any other pins that don't stick out as much as the rest. If you see any, scrap the chain. If not, it bolsters the bad splice theory, and you can reuse it. Don't forget that it'll now be 1" shorter, so make sure it can loop the big/big combination with another 1" to spare. If so, all you need is a chain tool and you're good to go.
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Old 09-11-12, 08:51 AM
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The second photo shows what appears to be a master link in the chain. You could remove the failed link and replace it with another master link, which would result in a chain which was the same length as the original. If you should instead decide to replace the chain (which might be a prudent course) I always recommend closing it with a master link for ease of future maintenance.
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Old 09-11-12, 09:48 AM
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Originally Posted by dsbrantjr View Post
The second photo shows what appears to be a master link in the chain. You could remove the failed link and replace it with another master link, which would result in a chain which was the same length as the original. If you should instead decide to replace the chain (which might be a prudent course) I always recommend closing it with a master link for ease of future maintenance.
Weird. Derailleur chains of that era did not have master links. I would guess that the chain has been replaced already.

A new "8-speed" chain would be a suitable replacement, complete with master link if you so choose: https://www.nashbar.com/bikes/Product...oductId=200391

IMO, the existing chain probably has rust inside from sitting around. I bet other links are in similar condition and ready to let go.
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Old 09-11-12, 11:49 AM
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Appreciate the comments. Will consider my options.

Yeh, I know nothing about cycling. Chain blew apart coming out of a steep turn and on an incline. On the pedals a bit and I probably have been a bit harsh with the shifting under load since I started riding it a couple weeks ago.

Not certain how much riding I will do if my legs stay healthy for running. Ended up doing unscheduled run back to truck after chain break, and I am feeling ok, so bike is not priority.

Pulled crank assembly apart chasing down squeal, and left cone is badly pitted, so I have one on order. Not certain how much money I want to put into this thing.

SRAM PC850 (8 speed) is 114 links. My chain is 118. Problem?
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Old 09-11-12, 12:07 PM
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Derailleur chains of that era did not have master links.
Yes that puts a premium on the attention to detail of the person who re joined the chain.

I'm guessing the OP did not put that chain on 30 years ago, themselves.
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Old 09-11-12, 02:31 PM
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Don't overthink this. 8 speed chains are cheap.
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Old 09-11-12, 02:52 PM
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Originally Posted by Jeff Wills View Post
IMO, the existing chain probably has rust inside from sitting around. I bet other links are in similar condition and ready to let go.
From looking at that chain, I'd say probably not. The chain looks in good if not pristine order.
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Old 09-11-12, 03:00 PM
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Originally Posted by wroomwroomoops View Post
From looking at that chain, I'd say probably not. The chain looks in good if not pristine order.
"Pristine" as in "early"? There's rust on the side plates and pins -- pitch it!
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Old 09-11-12, 04:27 PM
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Originally Posted by ThermionicScott View Post
"Pristine" as in "early"? There's rust on the side plates and pins -- pitch it!
+1 Chains are cheap, pitch it and replace.
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Old 09-11-12, 06:18 PM
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Ok. I guess I should temporarily reassemble the crank and figure out what length chain I need. I have no idea if this old chain is of proper length or if I can even safely remove a couple links. I also do not know if a single, new 8sp chain would be long enough.

Thanks everyone.
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Old 09-11-12, 06:27 PM
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Originally Posted by bsf View Post
\... I also do not know if a single, new 8sp chain would be long enough.

.
New chains are sold longer than most riders need, so it's a matter of cutting extra off. The chain has to be long enough to loop the big/big + 1" to spare, and short enough that when on the small/small the RD can take up the slack. On most bikes there's an inch or two between these, and you have some latitude. I prefer to us the longest chain possible, others the shortest, and Goldilocks uses something in between.
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Old 09-11-12, 06:40 PM
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Originally Posted by FBinNY View Post
New chains are sold longer than most riders need, so it's a matter of cutting extra off. The chain has to be long enough to loop the big/big + 1" to spare, and short enough that when on the small/small the RD can take up the slack. On most bikes there's an inch or two between these, and you have some latitude. I prefer to us the longest chain possible, others the shortest, and Goldilocks uses something in between.
Yeh, I got that in my reading over the last couple days. SRAM PC850 is advertised as only 114 links. My old chain is 118, though. Unless my current chain is excessively long, I am thinking I will need to splice 2 new chains. Am I missing something?
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Old 09-11-12, 06:44 PM
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Originally Posted by bsf View Post
Yeh, I got that in my reading over the last couple days. SRAM PC850 is advertised as only 114 links. My old chain is 118, though. Unless my current chain is excessively long, I am thinking I will need to splice 2 new chains. Am I missing something?
118 is very long. Even 40 years ago, before they started pinching pennies, chains sold with more than 116 links were rare. Before buying, put your crank back on, and loop your chain over the big/big combination to see how much room you have to spare, or if you really do need all 118 links. Then decide accordingly. If you do need all 118 links go on the recumbent forum and commiserate, those guys need 2-3 chains per bike.
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Old 09-11-12, 06:48 PM
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Ok. Seems I have all the info I need. Very helpful forum and people. Thanks.
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Old 09-11-12, 10:45 PM
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Originally Posted by FBinNY View Post
118 is very long. Even 40 years ago, before they started pinching pennies, chains sold with more than 116 links were rare. Before buying, put your crank back on, and loop your chain over the big/big combination to see how much room you have to spare, or if you really do need all 118 links. Then decide accordingly. If you do need all 118 links go on the recumbent forum and commiserate, those guys need 2-3 chains per bike.
That would be me. My recumbents use 2 1/2 to 3 1/2 "normal" chains, each. The upside is that they last 2 to 3 times as long.
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Old 09-12-12, 02:43 AM
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Originally Posted by ThermionicScott View Post
"Pristine" as in "early"? There's rust on the side plates and pins -- pitch it!
There's some, but overall, that chain is fine. The elongation measured by the OP is small. I'd totally use that chain.
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Old 09-12-12, 09:09 AM
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Originally Posted by wroomwroomoops View Post
There's some, but overall, that chain is fine. The elongation measured by the OP is small. I'd totally use that chain.
My concern is the rust that we can't see from the outside -- if there is corrosion between the side plates and the pins, the chain may "let go" in another place. As I do a lot of standing when climbing or starting from a stop, there's no way in hell I'd keep using this chain.
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Old 09-12-12, 09:34 AM
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Originally Posted by ThermionicScott View Post
My concern is the rust that we can't see from the outside -- if there is corrosion between the side plates and the pins, the chain may "let go" in another place. As I do a lot of standing when climbing or starting from a stop, there's no way in hell I'd keep using this chain.
Well, we at least can see one pin, and it looks fine.

Originally Posted by bsf View Post
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Old 09-12-12, 09:43 AM
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Originally Posted by ThermionicScott View Post
My concern is the rust that we can't see from the outside -- if there is corrosion between the side plates and the pins, the chain may "let go" in another place. As I do a lot of standing when climbing or starting from a stop, there's no way in hell I'd keep using this chain.
The chain failed via the basic plate pushed off the pin mechanism, not due to rust. IME I've never seen a chain break because of rust (wear faster, yes, break no) except where the rust was severe enough to weaken plates to the point of failure (cracking, not being pushed off).

Rust shouldn't be the main concern, plates pushed out elsewhere on the chain should be. That and preventing the problem by not shifting under load.
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Old 09-12-12, 09:51 AM
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Ah, okay. I've never had a chain break by any mechanism, but I had read that rusty chains were more likely to. Perhaps the real reason was that they'd been abused in general -- like shifting under heavy load.
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