Chain Skip Woes -- Help!
 

I put on a new chain, and I am getting skipping. The cassette only has 2,100 miles on it, and has never been used with a "stretched" chain. The chain I just replaced had not yet reached the ".75" limit as measured by my Bike Hand gauge. I think the skipping is occurring on the chainring, but it's hard to tell.

Here are the symptoms:

1. It only skips when on the small chainring. I've tried pretty hard to get it to skip when on the big ring, but have been unsuccessful. The small chainring also has 2,100 miles on it, although I bought it new. It doesn't seem worn (see photos). I have to push quite hard to get it to skip.

2. It skips most when on one of the smallest four cogs, but going up a long hill, standing up I had it skip once on the largest, and once on the second largest.

3. Twice today it skipped when starting from a standstill, and the chain dropped off despite my dog's tooth chain catcher.

4. I used the same number of links in the new chain as in the old. If I cross-chain to big-big, it jams (I don't think it ever jammed before).

5. I checked every link, and there are no frozen or sticky links.

6. I never had any skipping

Below are photos.

What do I need to do to fix this? Thanks!

http://i.imgur.com/BriSdWu.jpg
http://i.imgur.com/2I8W4w5.jpg
http://i.imgur.com/o35moKH.jpg
http://i.imgur.com/cjwLWiD.jpg

Hmm, chainrings look fine. Is there any rattle when you're just riding along?

I wonder if the pawls in your freehub are on their way out... got another wheel you can try temporarily?

No. Everything is smooth and quiet otherwise.

Doesn't feel like that. And remember, this went from zero problems to skipping with the new chain.

Ah, right. Hmm, same chain brand/model?

This is classic for new chain old cassette mix. The chain wear guidelines are only that - guidelines, but there are a number of other variables such as sprocket use mix, and the ratio of roller wear to pin wear. Stretch measures pin wear, but roller wear is just as important, maybe more so.

I don't know how bad the skip is, but if it's manageable on flat ground you might try living it for a while. Often with a bit of break in the new chain will run OK and the skipping resolve.

For future reference, consider alternating 2-3 chains on the same cassette. This keeps all the chains matched for wear with the cassette. and you can take the whole set well beyond the typical wear guideline. Also platooning the chains allows you to properly wash them while they're off the bike. You can rotate at any interval you're comfortable with, maybe based on how dirty the chain gets, or the service life of your chain lube. One advantage of rotating based on oil service life is that you won't be oiling a dirty chain.

I agree, but have you ever heard of a cassette wearing out before the chain does?

No, a very different brand and model. The last one was this one. I can't figure out how that would cause this, though, can you?

Yes and no. Chains and sprockets generally wear together. But as I said in the prior post, measuring stretch is only an indicator of chain wear, not a true measurement of that wear. Roller wear, which doesn't show up properly in the stretch measurement is just as important. In fact the best measurement of wear is how the chain actually meshes on the sprocket, but that's difficult to do reliably.

The best evidence that your sprockets are worn is that an older chain runs on them and a new one doesn't. You can confirm that with a new cassette of the same brand (don't toss the old stuff yet), and if your new chain runs on a new cassette of the same brand than you know for sure that your problem is sprocket wear.

At one AM I woke up and thought I had the solution: Due to item 4 I thought I'd routed the chain incorrectly through the pulleys. I couldn't go back to sleep until I knew, so I went down the garage, but no, the routing is fine.

It's very annoying, and even life-threatening. Yesterday I made a left from a stop in front of an oncoming truck and it skipped. Not a close call, but if the chain had come off...

I pulled the old chain out of the garbage, and I'll test out some things.

A little research is showing me that cassettes can indeed wear out in 2,000 miles, so maybe it's as simple as that.

But wouldn't I be able to make it skip when in the big chainring??

I use paraffin lubing -- perhaps that's rougher on cassettes, since the lube is likely to wear off faster on the outside??

OK, I missed the part about it skipping only on the small ring. That might be torque (chain tension) related, or it could be good evidence that the sprockets are OK (which is why I always suggest saving old parts replaced because of suspected wear).

The upper pulley for each sprocket is different depending on the chainring. I'd reconfirm hanger alignment, and bring the B screw in to push the RD down about 5mm and see if anything changes.

I saw that you're running a 38T small ring, the smallest you can put on a 130BCD crank. I had this mental image of a chain with slightly-taller sideplates riding up on the crank spider and causing the chain to skip over the teeth if everything was just "right" with enough torque. (One of my bikes also has a 38T on a 130BCD crank, and I can see marks on the spider where the chain makes contact, but I've never had any trouble with skipping.)

That's all very speculative, but I can't see how cassette or chain could have worn enough in 2100 miles to cause the skipping in the usual way, especially since you were careful to change the old chain at a prudent time.

IOW, the new chain is different enough such that problems with RD alignment or having a 38T small chainring now cause skipping.

Alternatives:

1. Buy a new chain of the same type as the old one.
2. Buy a new 45North chain, but get a 9 speed even though I have an 8-speed cassette.
3. Buy a 39T small chainring
4. Adjust the RD position.

BTW, here are the old and new chains lined up together. Note the lack of stretch.

http://i.imgur.com/RY0XGE3.jpg

I discarded the old one, because my attempt to remove some rust with OSPHO made it freeze up. I'm trying to rehabilitate it now.

Al,

Don't spend money before eliminating possibilities.

Since you report skipping on multiple rear sprockets, but only one chainring, there's a strong possibility that the skipping is happening up front, and not in the back as you report.

Possibly the chain coming from the outside is snagging on a pickup pin of the outer ring, and lifting off the inner momentarily, or as Scott says, riding the face of the outer and tips of the inner.

Or it could be that the new chain is marginally narrower between the inner plates, and sticking on small sprockets as it spools on. Then possibly the lube is enough to stiffen the plates just enough that a bent link comes off the jockey wheel and doesn't spool properly. This is happening only in the slackest chain positions (small.small) and the slightly higher RD cage tension in other combinations is enough to make a difference.

I still say you should experiment with the B screw and push the RD down. If nothing else, it will slightly increase chain tension.

In any case, if you do buy anything else, don't discard what may very well be good parts.

That's my (farfetched) theory, anyhow. You might look at the ends of the crank spider to see if the chain plates are leaving any impressions in the aluminum. Rather than replacing the chainring with a 39T or bigger (which would rule out my theory if you've got one lying around), you might then use a Dremel or similar tool to take a tiny amount of material off the spider to allow the chain to settle fully.

I took the 39 tooth chainring off my daughter's bike, and put it on mine, and that seems to have fixed the problem. I did testing up and down my street, putting the chain on cogs 2-4, respectively, and really mashed down on the pedal. I did some more testing on a seven mile trip. Couldn't get it to skip.

So, for now, until I feel like experimenting more, I'll go with that. I could tell that my lowest gear wasn't as low as before. Perhaps I'll put the 38T ring on again when I buy a new, narrower chain.

Scott, I didn't quite understand what you were saying about the spider...

http://sheldonbrown.com/images/crank-forged.jpg

Thanks for the help.

As for the mystery of why the new chain jammed on Big/Big: It rides up such that the plates on the side of the chain are on the top of the teeth of the biggest cog.

Not the greatest picture, but here's my 38T ring on a 105 (6-speed era) crank. You can see a smudgy spot where the chain is able to contact the tab on the crank spider.

http://i36.photobucket.com/albums/e2..._unrotated.jpg

My mental image is that of the chain not being able to settle completely at these spots, so it's a little more likely to get pulled out of position when under tension. One wouldn't compromise the integrity of the crank by Dremeling off a tiny bit of material at these contact points, methinks.

You mean this smudge?

http://i.imgur.com/OG3ZIjn.jpg

I sure didn't see any indentations there.

Yep, hmm... I can't think of any other reasons why an 8-speed chain might skip on a chainring or 8-speed cassette, given your care and mileage. Will have to get back to you if something comes to mind! Have you since tried going back to a regular oil lube?