Pot hole causes chain to loosen

On my way to work, on a dark and drizzly morning, I hit a new, but nasty pothole, while doing about 90 kph. All seemed fine until I got close to work, where at the slower speed and shifting gears, I noticed a scary clunking noise. It turned out that my chain had become slack. I know it was fine, before the incident, because I'm anal when it comes to doing the pre-ride inspections.

The pinch bolt was found to be quite secure, when I readjusted the chain. After it was adjusted, everything was good on the return trip.

Has anyone every heard of this happening before?

 

You would think it would just the opposite, with the force of the hit driving the rear wheel back, making chain tighter. Or, with the single side arm, chain adjustment is by rotating eccentric hub, so maybe the force cause hub to rotate in the loosening direction. Chains don't stretch, they wear, I would double check everything in the rear suspension.

 

This is not a 100% true statement. Yes chains do wear, the rollers do wear over time causing slack. But the links also stretch causing excess length in the link and is cumulative over many links. Also the sprockets wear causing greater distance between the teeth. All of these things together are why chains need adjusting.

If you don't believe that chains stretch measure your new chain with tension on it from end to end. At 10,000 miles measure the same chain under the same tension and you will have a difference in their lengths. This is normal. New chain technology has reduced the chain wear and stretch but it the nature of the beast.

Well maintained chains wear and stretch less, But constant slamming of the throttle will increase chain wear and stretch even if maintained well.

Why your chain appeared to stretch when hitting a pot hole is unknown. There are many factors that may have cause and adjustment movement. I highly doubt that the chain actually stretch because of the impact.

 

You think that maybe your chain appears to stretch could be that the holes in the pivot points may have worn and become elongated. I doubt the links stretched. But same end result I guess. A discussion that no one will win. Just like oil.

Does not make sense to me why your chain would become loose. Then again, which way do you crank your spanner to tighten the chain. If the pot hole was that sharp, I guess the cinch bolt may have given way.

 

I don't know whether a link will stretch or not but has anyone measured a single link on a worn chain vs a new chain?

 

That would be interesting to see. I may keep that on mind when a new chain is needed which may not be that far away. I think the measurements would need to be do e with a measuring device far more accurate than my Stanley tape measure and probably better done averaging several links. But nothing that can't be overcome.

 

I think the best way to put the chain stretch debate to bed would to measure the chain end to end and then measure the space between the links and the link plate themselves when the chain is new and prior to putting it on the bike. Then when you replace the chain, retake these same measurements and see what the difference is. I'm not due for a new chain for sometime, at least that's the way it looks right now, but I would willing to do this for my next chain replacement. Of course waiting for the data to come in could take sometime!

In the mean time see if this will help dispel the myth...
https://www.facebook.com/notes/klim/busting-motorcycle-chain-myths/416157056989

 

perhaps you need a new chain-is it stock? I am running the best 520 chain made

 

Chains DO NOT STRETCH, period. They wear at the pins where each link is connected. The pins wear in the thousands. You have a chain with 110 links, each pin wears .005" your chain is now .550 longer, a little more than 1/2". If each pin wears .010" then your chain is over one inch longer. The side plates do not stretch, elongate or magically get longer. Measure a new chain and an old one's side plates, you'll find they are the same size. It's the pins that hold the inside plates together that get smaller/compressed. Just grind some out and take a look at them.

Just like wear and tear on an engine. You can't tear an engine cause it's a big iron block. I seen one once...............

 

Thanks Grey for saving me the time to type out the same things. And sprocket wear is usually faster than the pins wear making people think there chain stretched. Keep you shit clean and it will last a long time.

 

Again another argument that won't be won because someone read an article on the internet.

 

No arguments here, pins wear in holes and sprockets wear down. That fact has been know for a very long time.

 

So, than what your saying, is that it is possible my chain is stretching. I knew it!

 

Since I had a chain replacement to today's to do list, I took some pictures and measurements, comparing the old and new chains. With one end held in place, I first stretched them as long as they'd go, then pushed them together to as short as possible while still straight and flat.




The old chain is about an inch longer than the new one (same link count), and has about the same amount of additional "slop" between the links.

No internet research went into this post, but you're reading it on the internet, so you know it's true.

 

All this talk about chains stretching (or not ) is fascinating, but I don't believe that karazy's chain magically, evenly stretched when he hit the bump. The logical explanation is that the eccentric rotated a little and gave him slack. I'd be investigating that before worrying about whether the chain is wearing. I've read that if you are missing a washer on the pinchbolt, the bolt shoulder can "bottom out" without applying full tension to the eccentric. If that is in place, I would check the torque on that bolt.

 

One of scenarios I put forth in post #2, but everybody jumped on the chain stretching.

 

With apologies for having gone OT, I agree. There is virtually zero chance that "stretching" of the kind associated with wear/usage would happen suddenly. An instantaneous load sufficient to make it that much longer would certainly have broken the chain.

 

I didn't notice a washer there and the parts list doesn't show one. It has been years since I've had to adjust it and it has held just fine. As stated earlier, the bolt was tight and there have been no problems since fixing it. I'm not sure what freak set of circumstances aligned to cause this to happen, but we'll have to assume that the bearing holder rotated.

With that much stress put on the chain, I guess Ill be changing it out this winter. I'll check for scoring while I'm in there.

Chain stretch, who's crazy now. bahahaha

 

I think from the data, I'm going to swap my Oring chain for a non-Oring to make my bike lighter so I can go faster. A couple of ounces is a couple of ounces or if going metric, a couple of ounces is a shitload of milligrams.

 

That right there is smart thinking Billy. When I did a sales course years ago, we were trained to express costs in the biggest unit, and savings in the smallest. So I only weigh 0.085 tonnes, but I could save as much as 2300 grams by fitting a Shorai battery.