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what causes chain and cog wear?(15 posts)

what causes chain and cog wear?DougSloan
Aug 1, 2003 7:06 AM
Despite Sheldon Browns' information, I'm not understanding what causes chain and cog wear. I assume there are two potential causes: 1. friction; 2. tension.

I can understand friction wearing the tiny pins within a chain as it curves and straightens about the cogs and pulleys. With such limited movement at relatively slow speeds, though, it doesn't seem that it would be signficant. Another type of friction would be the chain pulling on the sides of the cog teeth.

In either event, I could see lack of lubrication or contamination causing increased wear. However, I'm questioning whether friction is the main culprit, or whether it is the tension from pedaling. Tension pulling the chain and putting pressue on the cog teeth, over time, and to varying degree, depending up your power, what gears you typically use, and cadence.

What do you all think? What is the real cause for chain and cog wear?

Doug
My impression, from some old study I read,OldEdScott
Aug 1, 2003 7:52 AM
is that dirt's the main cause. Don't remember where I read that, but I must have taken it as gospel since I've sort of maintained that belief. Was it some study that said you don't even really need to lube a chain, because the metal-metal contact isn't a serious cause of wear?
I though it wasovertrained
Aug 1, 2003 8:35 AM
tension stretches the chain and the longer chain causes friction when running over the cogset which wears them down. I heard that in motorcycle test a clean and well lubed chain is about 10% more efficient.
No, no, no!!!Alexx
Aug 1, 2003 12:52 PM
Nothing in a chain actually stretches. The ELONGATION is caused by wear in the pin bearing surfaces. If you actually STRETCH any part of a link, it will break very, very quickly.
no!C-40
Aug 2, 2003 6:23 AM
Tension does not stretch the chain. A chain gradually becomes longer do to wear on the pins and rollers.
follow-up questionsDougSloan
Aug 2, 2003 9:30 AM
The clearance between a pin (which wears, I understand) and the link must be very, very small. Can grit really get in there to accellerate the wear?

Also, wouldn't greater tension cause greater friction on the pin, resulting in accellerated wear (which we see as "stretch")?

Thanks.

Doug
follow-up questionsJimP
Aug 2, 2003 12:47 PM
Doug,

Have you been caught in the riding in the rain after a dry spell? After a while you can hear the grit in the chain and gears grinding and squeeking away. I have had that happen and then run the chain through a chain box cleaner and found an amazing amount of junk in the bottom of the box. A little road dust is just a very fine sand. That seems to be able to work itself between the plates very easily and then it is where the pin rides on the plate causing the wear.

Jim
follow-up questionsLC
Aug 3, 2003 8:03 AM
If oil can get in, then so can dirt. That is why in the home brew you mix in the mineral oil; it helps to flush out the dirt.

Greater tension does cause more wear, but then so does higher rpms. Eccentric loads (i.e. cross chaining) also increase the forces one one side of the chain and causes more wear.
metal-metal contact isn't a serious cause of wear...innergel
Aug 1, 2003 12:32 PM
You also lube the chain to keep the links moving freely. If all those links and pins are stiff, pedaling will be more difficult and thus less efficient.

Wear is only one reason to lube up.
Changes in tension?Dave Hickey
Aug 1, 2003 9:02 AM
I'm not sure other than to say the chains on my single speeds last a lot longer than than my nine speed bikes. My single speeds both run 8 speed chains. In a multi-geared bike, maybe the changes in tension cause the bushings to wear faster.
re: what causes chain and cog wear?MR_GRUMPY
Aug 1, 2003 10:50 AM
A chain elongates because of the wear at the pin bushing interface. The pins wear down to a smaller dia, so that the distance between links gets larger.
The more worn a chain is, the more in wears down the Aluminum teeth on the chainrings. The chain engages the teeth higher and higher as it wears.
The solution is to keep your chain well lubed, and change it when your Park Chain Checker says to.
Ps. Stainless Steel chains will always wear faster than carbon steel chains. The only purpose of stainless chains, is either because of highly corrosive enviroments or because you can't lube them.
It's simple really - grinding compoundKerry Irons
Aug 1, 2003 4:32 PM
While there will be a small amount of wear by metal to metal contact, wear is essentially caused by the "grinding compound" that is formed from dirt and metal shavings/flakes. It's sort of due to friction - the friction between the grinding compound and the metal surfaces. Held in place by the lube, this stuff wears away the metal surfaces in the pins and bushings of the chain and on the faces of the cogs. If you could run your drive train in a sealed compartment, wear would be significantly reduced as the only source of abrasive would be the metal itself. If you ran the drivetrain in a sealed compartment with a flush of fresh lube to continuously remove any solids, things would last a lonnnnnng time. As it is, you can maximize drive train life by keeping things lubed and clean.
It's simple really - grinding compoundJimP
Aug 1, 2003 6:09 PM
Kerry has stated the cause quite well. I just wanted to add that just .005 in ( that's 5 thousandths of an inch) wear in each link will create a "stretch" of 1/8 inch in a foot of chain - the measure that says your chain is junk. Many auto engines use timing chains that are in a sealed, continuously lubed with fresh, filtered oil that last over 100,000 miles. A recent article stated that the author was going to replace a timing chain on an engine with 125,000 miles but it measured as a new chain because the owner had changed the oil & filter every 3000 miles. A clean, lubed chain lasts longer.

Jim
re: what causes chain and cog wear?M_Currie
Aug 1, 2003 6:32 PM
I think dirt and abrasive slurry are the main culprits, as stated here, but wonder too if shifting is a factor. Industrial and non-derailleur chains don't have to flex sideways, so they can also be sealed better, but I would expect the flexing under load to accelerate wear. A 3-speed with a fully enclosed chain can go just about forever.

Another thing to remember, though, is that non-derailleur cogs are shaped differently, so that an elongated chain will still track on them without jumping. An industrial chain can ride further out from the center as it wears, without rolling over the tops of the teeth. Even if they wore at the same rate, derailleur cogs would be less tolerant because of their stubby teeth.
re: what causes chain and cog wear?John Ryder
Aug 1, 2003 7:17 PM
Installation. If you don't put the chain on.... it will never wear.