Chain "Stretch" - Part 3 (diagrams)

After talking to a few friends trying to explain "chain stretch" I have decided a picture is worth a thousand words... so I built a few illustrations showing chain wear.

The pin, showing in black, wears away by rubbing the (orange) housing. This creates a looseness that increases its length.

When the chain is longer it rides up on the teeth of the gear reducing the contact, allowing it to "skip" under hard pedaling.  It will also wear the tooth away when it rides the incorrect location of the tooth, effectively eating it away.

So keep your chain clean and lubricated. And replace it when it gets "stretched."

Part 1: Measuring Chain Stretch
Part 2: Free Wheel Removal
Part 3 (this post): Chain Stretch Diagrams

Chain "Stretch" - Part 2 (freewheel removal)

I recently did a post about measuring chain "stretch" and found my son's drivetrain was indeed worn. This Saturday I was finally was near a local bike shop during open hours to pick up the needed tools.

Because the part needing replacement is the freewheel I needed to get a special tool. When choosing the tool you will need to know the brand freewheel and the number of splines inside (grab a flashlight, look down into the slot, and count). In our case, the freewheel was made by Shimano and has 12 splines. So we picked up a FR-1 from Park Tools. If you are not sure which tool you need, go to this page on Sheldon's site or take your wheel to the bike shop and they will tell which you need.

The FR-1 fits into the freewheel and using a big 1" wrench turn it counterclockwise. In theory. Because it is self tightening, it is very difficult to turn. The longer the wrench, the better the chances of getting it loose. Ours was not budging.

Just I was headed out to the garage to look for a "cheater bar" (another tool added to the end of the original wrench to lengthen it), I remembered another trick I had recently heard. If you mount the FR-1 into a vise, you can use the wheel itself to loosen it.

First step is drop in the tool. Then put the nut or quick-release back on the wheel. This holds the tool on for you (a good idea when using a wrench also).

 Next mount the tool in the vise TIGHTLY. Grab the wheel and twist counterclockwise. With enough struggle, it will come loose.

Once it was loosened, it easily came off with a lot of turning.

The install of the new freewheel is much easier. Simply spin it on finger tight. The pedaling motion will tighten it to the "correct" torque.

The old freewheel is clearly worn. Most areas between the teeth are no longer perfect half circles as a new one would. This is great time to replace the chain and front chainring also as they will also be worn too.

We will be paying more attention to keeping it lubricated and checking the chain in the future.

How to Measure a Bike Chain for "Stretch"

I always go over my son's bike after a long offroad rides, cleaning, looking for anything broken, etc. This time I realized I had never checked his chain for wear. So, out came my trusty ruler. I know the bike was not well taken care of before we purchased it so I was not too surprised with what we found: it was clearly "stretched." It is time for a new chain and more than likely a freewheel.

How did I know it was no longer good? Let's measure the "stretch." Using an inch ruler, put the "0" in the center of one of the chain pins and go down to the 12" mark. When the chain was new, the 12" would be exactly in the center of a chain pin.

In our case the chain pin center was more than 1/16" past the 12" line.

Stretched chain? Well, not really. What is happening is the tolerances between the parts are getting looser. More space, the longer or "stretched" the chain becomes.  With any wear item determining how much wear is too much is the difficult part. According to every biker's favorite info website (Sheldon Brown's Bicycle Tech Information Site):

• Less than 1/16" past the mark, all is well.
• If the rivet is 1/16" past the mark, replace the chain, but the freewheel/cassette sprockets are probably undamaged.
• If the rivet is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.

Clearly we have waited too long. We plan to get a new chain. And though we might get away without changing anything else, we plan to use a "parts bin" freewheel I have.

Watch for an update soon, after I gather parts and tools, showing how to change the chain and freewheel.