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Old 08-23-2019, 11:32 AM
batman3n1 batman3n1 is offline
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Default Question

Quote:
Originally Posted by turboimark View Post
Understanding chain elongation and how to predict failure

Hey guys,

So I have been riding around the woods for a while now and it's time to change my drive chain and I figured I would give a brief walk through on understanding when/how your chain wears and how to predict failure.

I see a lot of guys seem to be in one of two camps. Either they a) run the chain until it snaps or they b) change it every -x- amount of hours regardless of condition.

In short, there IS a way to predict chain failure and it can help save you a ton of downtime and also a lot of money on unnecessary chain replacement.

And the best part of it? It's FREE. That's right, all you need is a tape measure and your eyeballs!

CHAIN PITCH

"Pitch" is the measurement of the chain from center of pin to center of pin of one link. This is the standard way every chain is measured. There are 4 main standards for chain measurement: ANSI, BS, Motorcycle, and "Engineered". For the sake of this, we will focus on "ANSI" standard chain.

ANSI standard chain is the most commonly used chain in the world and extremely common in go karts and pocket bike applications. You normally will see these chain sizes written as #35, #40, #41, #50, etc. which is the ANSI standard for chain.



All ANSI chains are based as a fraction of the number 80. So a #35 chain is 35/80 = .4375 pitch

#40 chain is 40/80 = 1/2" pitch chain.
#50 chain is 50/80 = 5/8" pitch chain
#80 chain is 80/80 = 1" pitch chain

And this goes all the way up to #240 chain which is 240/80 = 3" pitch chain.
So, how does this help me?


HOW TO PREDICT FAILURE


Well, we know now what the STARTING LENGTH of the chain is new out of the box.

So with that logic, we can measure the used chain and use the percent difference to determine when it will fail.

EXAMPLE

So for example if we have a brand new section of #40 chain and we measure 10 links of it, then:

10 links x 1/2" per link = 5" total length (NEW IN BOX)

So if we ride this kart for a little while, then re-measure, we may find the 10 links to now be 5.10" total length.

NEW IN BOX LENGTH = 5.00"
USED CHAIN LENGTH = 5.10"

If we take the percent difference (old-new / new) *100 = ((5.1-5)/5) *100 = 2% elongation.



So in this case, you should start looking at replacing the chain.

As a rule of thumb, chain should be replaced between 2.5-3.0% elongation.

The reason behind it being that chain wear is linear from 0-3% but after 3% the hardness generally has been worn off of the chain and the chain will snap unpredictably. I've seen guys run them further than that, even up to the 7% range but it's very obvious there is stretch in the chain at 3% and that will be evident through slapping, rattling, etc. Also, being out of axle adjustment (takeup) is a big indicator as well.

tl:dr

Measure your chain regularly. If it has grown 2-3% then it's time to replace it or else you will find yourself stuck out in the woods.
(Disclaimer) I'm new here. my CT200u-EX uses a 420 chain which wasn't on the table. How do I compute stretch.