# Chain checkers not accurate?



## aBicycle (Jun 13, 2012)

So, according to the ruler I probably have less than a 32nd of an inch of wear, but for some reason I can cram my park chain checker's .75 dongle through my chain.

Is it normal for the chain checkers to be this inaccurate? I mean, I should have at least a 16th of an inch of wear according to that checker, but that is not the case.


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## customfab (Jun 8, 2008)

Are you using the park checker with the moveable end? Those aren't very accurate. I much prefer the plate style which park, rohloff, shimano and a handfull of others make. Unless you're in the business of selling chains that is.


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## mitzikatzi (Sep 9, 2008)

Here is one view on it. 

Chain Wear Measuring Toolsl

I just use a 12" steel ruler.


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## epic (Apr 16, 2005)

Measuring pin to pin doesn't tell you the whole story because there is wear on the bushings also.


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## jimPacNW (Feb 26, 2013)

If you use the Metric side of a 12"/30.5cm metal ruler ($4? at the local cheap tool place), it's very easy to fit within the frame using the 25.4 (good/new) 25.5 (ok) 25.6mm (replace) measurements.


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## nov0798 (Nov 27, 2005)

Just replace it every season or 6 months if you can ride year round, and dont worry about it. Chains are cheap.


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## bad mechanic (Jun 21, 2006)

epic said:


> Measuring pin to pin doesn't tell you the whole story because there is wear on the bushings also.


Do you mean the bushing or roller? If you mean bushing, then measuring pin to pin will tell you the bushing wear as well. If you mean roller, then roller wear doesn't really matter.


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## bad mechanic (Jun 21, 2006)

Trust your ruler.


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## epic (Apr 16, 2005)

bad mechanic said:


> Do you mean the bushing or roller? If you mean bushing, then measuring pin to pin will tell you the bushing wear as well. If you mean roller, then roller wear doesn't really matter.


Bushing and roller actually. When they wear it allows the chain to sink deeper onto the cog which effectively changes the diameter of the cog so that the spacing is wrong. The Shimano CN41 tool measures this.


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## thickfog (Oct 29, 2010)

epic said:


> Bushing and roller actually. When they wear it allows the chain to sink deeper onto the cog which effectively changes the diameter of the cog so that the spacing is wrong. The Shimano CN41 tool measures this.


Not really. Roller wear does not matter. http://pardo.net/bike/pic/fail-004/000.html


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## bad mechanic (Jun 21, 2006)

epic said:


> Bushing and roller actually. When they wear it allows the chain to sink deeper onto the cog which effectively changes the diameter of the cog so that the spacing is wrong. The Shimano CN41 tool measures this.


Sorry, but roller wear doesn't matter and doesn't change the pitch of the chain.

Please note that a chain bushing and a chain roller are not the same thing.


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## Varaxis (Mar 16, 2010)

epic said:


> Bushing and roller actually. When they wear it allows the chain to sink deeper onto the cog which effectively changes the diameter of the cog so that the spacing is wrong. The Shimano CN41 tool measures this.


I believe the reason why the ruler works is because the inner links will appear "elongated". Of course the plates don't get stretched, but the inner links are connected to the outer links through the pins, "bushing", and roller, and that wear will show, _if you measure with the chain in tension_.

The reason why the OP's chain checker is criticized is because it spreads the rollers out in opposite direction, when it should be measuring the distance between rollers as if the chain were in tension.

When people say roller wear does not matter, are they saying the abrasion from their outer circumference? Technically, roller wear where it meets the bushing, the inner circumference, most definitely matters, as long as you don't presume that chains wear evenly/uniformly.

This topic reminds me that I should lube the new connecting pin (Shimano) or quick link the next time I install a new chain. I forgot to do that last time, when I decided to see how long the original factory lube would last and had to lube the chain earlier due to an annoying squeak.

That pardo article is really good. If you can't be bothered to read through the whole thing, these illustrations basically sum up why the OP's chain checker isn't the most accurate:









^ OP's chain checker: bad way to measure









^ More accurate way to measure, since it gauges the distance between links as if the chain were in tension, rather than spreading the chain out.


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## bad mechanic (Jun 21, 2006)

Varaxis said:


> Technically, roller wear where it meets the bushing, the inner circumference, most definitely matters, as long as you don't presume that chains wear evenly/uniformly.


No. It doesn't. So long as they wear evenly (and there's no reason they don't) the roller wear _does not matter_.


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## Varaxis (Mar 16, 2010)

bad mechanic said:


> No. It doesn't. So long as they wear evenly (and there's no reason they don't) the roller wear _does not matter_.


Different torque loads (mashing vs spinning), shifting, cross chaining, jolts from hub engagement and ratcheting, uneven lubrication, abrasives from filth getting in there (mud), vibrations, chain slap, chain suck, lubrication getting washed out from puddles or whatever... hmm what else could possibly affect wear rates when actually mountain biking... all these small inconsistencies add up. Not uncommon to test chain wear in 2+ different spots in the chain and get 2+ different results.


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## bad mechanic (Jun 21, 2006)

Not to any reasonable extent.


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## thomllama (Oct 3, 2007)

bad mechanic said:


> Not to any reasonable extent.


I know there are many who think that way but, 
Sorry, but I have to hardily disagree with ya as I kinda just did a test over the coarse of 3 yrs on chains and drivetrains...

I can go into all kinds of details but summing it up.. I had a 1 yr old chain (quality KMC chain) that measured pin to pin less than 1/16th of an inch out,... but the bearings/bushings were so worn it hopped on a brand new chain ring and cassette so bad that just pedaling on a flat area it would do it, didn't even have to mash/climb to get it to slip/hop.

"stretch" is only one of the many wear point of a chain on your bike, checking the interface between where the chain interacts with the cassette/chain ring is as, if not more important than just checking pin to pin stretch.

As was stated before, really the best thing is to just replace your chain ever 6 months (more if you are a highly frequent rider, less if just a weekend/summer rider) this will prevent more expensive issues and make your cassette/rings last longer.


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## DennisF (Nov 4, 2011)

> ...I can cram my park chain checker's .75 dongle through my chain.


Don't cram it. Just let it drop in if it will. If you are using one of those flat go/no go checkers, you are probably flexing it slightly and making it "fit".


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## bing! (Jul 8, 2010)

This is my solution that I made a prototype. Its a simple clear ruler with a chain stretcher.

The marking are simplified to simply pass/fail.





You position the chain checker on the chain and the bar stretches it over a ruler. Making sure the right marked line is centered on a pin (it self centers), the left line has two marked lines. If the first line is centered, pass. If the second line is centered on the pin, fail. If its in between, its ok.


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## aBicycle (Jun 13, 2012)

The problem with that is that the plastic will not expand and contract at the same rate as the metal of the chain. Which is why they say to use a metal ruler.


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## bing! (Jul 8, 2010)

aBicycle said:


> The problem with that is that the plastic will not expand and contract at the same rate as the metal of the chain. Which is why they say to use a metal ruler.


huh?


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## AZmike (Jul 1, 2010)

Differing coefficients of thermal expansion.

Most metal rulers are stainless steel though.
Stainless steel is about 17 um/m-Kelvin
The steel used to make most chains is not. It's thermal expansion coefficient is 11-13 um/m-Kelvin. 

I'm not sure what the linear coefficient of thermal expansion is for the wood and plastic measuring device.

It probably doesn't matter though unless you're measuring the chain at temperatures very different that those that the tool was designed for. A 10 C temperature change (18 F) barely changes the length of the chain: 12*10*1e-6 = 0.00012 = 0.012%.


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## DennisF (Nov 4, 2011)

Good design and craftsmanship, Bing.

I did some quick web searches on thermal expansion and apparently plastic expands about 18 times more than metal.
Thermal Expansion Coefficients - Plastics - Engineer's Handbook
So multiplying AZMike's figure of .012% by 18, you get .22%. In practice, designing it and using it at room temperature probably puts you close enough.

However, glass is in the same ballpark as steel.
Coefficient of expansion for common glasses and metals
That would make a really classy tool. Not prone to scratching etc like plastic.

I know a little about wooden model airplane building. Wood expands and contracts based on humidity more than anything. (You leave a wooden airplane in a dry room a few days before covering it so that it will expand and keep the covering tight when taken outdoors. And ideally you use wood to connect the servos located at the front of the plane to the control surfaces in the tail, so that everything expands and contracts at more-or-less the same rate.)

The amount of expansion is going to vary with species and even the individual piece of wood. How much it actually expands, I don't have a good feel for.

It looks like you anchored the plastic closest to the zero-point with a round hole, and used a slot at the measuring end to allow for expansion and contraction of the wood without warping the plastic & vice versa. Good thinking. If you mount the fixed end of plastic or glass as close as possible to the zero-point, you will probably be OK. I haven't researched this either, but soaking the wood in an oil finish, and/or covering it with polyurethane would probably lessen expansion due to humidity.

Or just use a piece of light angle iron instead of wood.

Keep me and AZ in mind for a free unit if you go commercial


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## Ratt (Dec 22, 2003)

I actually find the Park cc2 to be highly accurate. When I lay down the new chain next to the old one for shortening the link is exactly one off like the checker says. Yes I can see how people would screw up using a cc2 and once you overtorque the tool its bent and useless. That being said the best way is to check is to use a caliper between the rollers. There is thread somewhere in this forum about the link count and the numbers you should see on the calipers. Yes harborfreight suks but for this purpose their $9 digital caliper is good enough.


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## mitzikatzi (Sep 9, 2008)

Ratt said:


> I actually find the Park cc2 to be highly accurate. When I lay down the new chain next to the old one for shortening the link is exactly one off like the checker says. Yes I can see how people would screw up using a cc2 and once you overtorque the tool its bent and useless. That being said the best way is to check is to use a caliper between the rollers. There is thread somewhere in this forum about the link count and the numbers you should see on the calipers. Yes harborfreight suks but for this purpose their $9 digital caliper is good enough.


according to this article they are not accurate.



thickfog said:


> ...snipp.. http://pardo.net/bike/pic/fail-004/000.html


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## DennisF (Nov 4, 2011)

> There is thread somewhere in this forum about the link count and the numbers you should see on the calipers.


http://forums.mtbr.com/drivetrain-s...ain-stretch-using-vernier-caliper-564317.html


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## Ratt (Dec 22, 2003)

mitzikatzi said:


> according to this article they are not accurate.


Harborfreight or the new chain


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## mitzikatzi (Sep 9, 2008)

The Park CC2 tool measures with an error according to that link.


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