Roller chain stretch

I've looked and Googled but can't find any real information. The argument is that a #40 chain will stretch as it's run. Speed is slow. It will
stretch more under heavier load but I say it will stretch under almost no load, it will just "Settle in". My antagonist maintains that it won't stretch measurably, if it is kept lubed, under extremely light load. Who's right?
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Settle in = wear.
Roller chains are metal-on-metal moving parts. They will wear unless stationary. How much wear are you talking about? Say each link wears 0.0001 inch. Multiply that by, say, 100 links. Your chain just grew a hundredth of an inch.
This is why they invented cam chain tensioners. And why motorcycle drive chains, and sprockets too, are considered disposable wear items.
You can't settle the discussion unless you put numbers on the assertions. He has to say, it will wear *less* than X, you have to say, it will wear more than that.
Jim
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On Fri, 18 Aug 2006 02:22:59 GMT, "Tom Gardner"

Hey Tom,
ALL chain stretches. Quality, speed, load, and turning radius, along with lube will have a definite effect as to how much. Running in a "loop" (endless) it will stretch equally per link. Rocking over, it will wear more on the portion that is rocking.
Roller chain stretch leads to sprocket wear, and that wear is non-correctable.
Take care.
Brian Lawson, Bothwell, Ontario.
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I think the "stretch" is wear of the pins, bushings, rollers and sprockets so is occuring whenever there is motion. Speed, load, lubrication, materials, and grit all obviously determine how rapidly. There is an initial "wear-in" at a higher rate. How long it would take to be measureable would of coursse depend on the measurement sensitivity available. I suspect that the chain manufacturere might be able to quantify the rate and then you would have to decide the acceptable limit. I have seen a few short, low speed drives where no adjustment is provided, but they are very much in the minority. Adjustment could be needed just to accomodate initial tolerances.
Perhaps you could design so that adjustment could be easily retrofitted if found to be needed.
Don Young
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My FMC weight sizer (apple packing line) uses A LOT of #40 chain. I've not had to tighten a single chain in 18 years of operation. I give it a serious lubing before each season. It runs 400 - 500 hours a year. Low speeds and loads, way below the stress limit of the chain. There's at least six very short chains where no adjustment is possible
Just one data point.
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My experience from motorcycles is: There are _huge_ differences in quality. DID chains were crap, JWIS were bad. The best chains (O-ring chains) come from Regina. Just breaking in and then they didn't change length. They kept for one season of MX-riding. I always sold the bike after a year. :-) Just light oiling with a chain lube. Oiling doesn't help that much on O-ring chains anyhow. But with conventional chains, you realy need eiter a chain lube spray, or even better cook them in MoS2 grease. Castrol has (had?) that stuff. Great!
Nick
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