Bicycle Mechanics - Chain Skip -- Running out of options
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11-29-04, 04:20 PM
I recently did a fairly significant, much needed rebuild of my wife's IF Crown Jewel with Campy Chorus components -- new bottom bracket, new chainrings, new cassette, new chain, new Ergo shifters, cables, and cable housing.
My wife is elated with the improved performance of her bike, but there is one problem that remains - chain skip. It is a pre- and post-rebuild problem. The skipping occurs when the chain is on the small chainring and on the larger cassette sprockets (she has an 11-29 10 speed setup), and only when there is a lot of tension on the drivetrain, particularly when climbing. She thinks (but is not certain) that the chain both skips without changing gears and skips while dropping to a smaller sprocket.
I have ruled out the following - chain size, chain wear, cassette wear, chainring wear, (all these are new), and indexing adjustment. As well, there is no indication that the derailleur mount has been bent out of alignment.
When I reviewed the Campy RD adjustment instructions, they said that the B Tension setting should be at full stiff, and so I set it that way. While shifting the gears on the stand, everything appeared OK and I did not make any adjustment to that setting. However, when we rode yesterday (first time with new ergo shifters) with the B tention at full stiff, the chain skip was more pronounced and occurred on even the third and fourth largest sprockets.
I am thinking that this chain skip problem may be related to the B tension setting, and possibly a worn-out spring in the derailleur (I cannot detect any movement of the top pulley when I adjust the tension screw).
If it is not the B tension setting, is there anything inside the freehub (I'm not sure about that nomenclature) that could be worn out and causing this skip? There's probably 10k miles on this bike and I haven't taught myself to dig into the hubs yet, so that is all original equipment.
Sorry for the long post. Any thoughts, advice, ideas would be quite welcome. Thanks in advance.
p.s. One other idea - what are the symptoms of worn-out RD pulleys?
11-29-04, 04:58 PM
Okay, here's one thing I've had that you might check: my chain only skipped on the smallest cog and I didn't know why. I eventually figured out that I had a slightly stiff link in the chain. Because the derailer is wrapping the most chain up when it's on the smaller sprockets, the chain is at the sharpest angles on the derailer pulleys. So if a link is slightly stiff it won't bend fully as it goes around the pulley, and this will cause the derailer to jerk forward and momentarily change the chain tension, which feels just like chain skip. The solution was to find the stiff link and really really loosen it up.
You should be able to detect this problem by turning the cranks slowly by hand and watching each link as it goes around the derailer pulleys.
Anyway, I hope this helps you. It's the only time I've ever had chain skip other than with a worn out drivetrain.
Your problem may be chainline related. It sounds like the chain angle has become too severe and causes the sideplates of the chain to catch on cog ramps and derail.
Ideally, when the chain is on the 5th largest cog and the small chainring, there should be little deflection in the chain. The same goes for the 6th largest cog and large chainring combination. If it is deflecting noticeably to the inside the centre of the freame in either of these two combinations, then there is a chainline problem.
Normally, a chainline problem results when new bottom bracket spindle is installed and has moved the chainrings further out from the bottom bracket. A new crankset can cause similar problems. However, in your case the problem existed prior to the component changeout, lesening the probability of a crankset/spindle issue. More likely, the rear triangle has been knocked out of alignment, affecting the chainline. Check this may running a string from one dropout, around the headtube , to the other dropout. The gap between the string and seat tube, should measure the same on both sides.
I also wouldn't rule out a bent derailleur, unless you have the shop tool to verify it.
11-29-04, 07:16 PM
As well, there is no indication that the derailleur mount has been bent out of alignment.
Well, the derailleur hanger is the first thing that I would check. Whenever you have a shifting problem that doesn't respond to the common fixes, the first thing to do is to make sure that everything is at the default setting. That means the derailleur hanger has to be straight. It doesn't have to be very badly misaligned to screw things up. Checking it isn't a big deal, but it takes a special gauge to do it.
11-29-04, 07:20 PM
I third the bent derailleur hanger
11-29-04, 09:30 PM
I forth the hanger. Also, did you use a quick/master link? Some of them I have seen cause skipping in the smallest cog only. It quit by just flipping the link 180 degrees fron to back. A just a little bit tight high limit screw can cause this problem as well as a link that is just a little to tight (Usually where the chain was joined) The B screw is probably contributing as well. I like to set it to where the chain runs smooth in the small front big rear combo. In theory the tension the der puts on the chain should make no difference. Going back to tech school days: The tooth, at the top of the cog in the pulling direction, takes almost all of the load. with the teeth behind it taking the slack if this first tooth is deficient. This makes me think chain problem as there are so few teeth running back up in that small cog.
it could also be the master link getting caught on something... it happened to me when the master link would hit the bash ring.
12-06-04, 11:43 AM
Turns out the RD was shot -- at least one of the internal springs is worn out and the pinion drive for the B setting was broken. I snagged a new '04 Chorus RD and installed it yesterday morning. The difference in shift quality is truly remarkable - and no more gear skipping under load!
Unless it turns out to be cost prohibitive I will try to rebuild the old one for a spare.
Thanks again to all for your suggestions.
Hmmmm... double or triple? Chainring sizes? Long cage rear der, I assume?
I ask because Campa do not offer an 11-29 cassette, though I had considered doing the same thing.
12-07-04, 04:42 PM
You are quite right regarding the cassette. My wife's bike frame is too small (the chain hits the seat stay)to accomodate a sprocket any bigger than an 11 on the outside, so I have to replace the 12 (IIRC -- might have been a 13) with an 11. This is mated with a medium cage Chorus RD and 53/39 chain rings up front. Works just fine that way. The bike is a tiny (custom) Crown Jewel with a pretty short chainstay, so the chain line is somewhat challenging with a 10-speed. In any case, I've manged to get it dialed in with the new RD.
Diagnosing these problems has been fascinating because of the earlier condition of the bicycle. My wife put at least 10k miles on this bike and did very little maintenance. When I took up riding earlier this year and took on the job of rehabilitating her I.F., it was the perfect bike repair project because everything was worn out! -- BB shot, index ratchet in the shifter broken, chain completely worn out, cassette destroyed by wornout chain, chainrings worn -- you name it.
I'm almost done rebuilding the bike (I have to choose rainy days to work because my wife doesn't want to give up and riding) and Sharon couldn't be happier. She says it rides like a new bike.
All the above are valid suggestions. I like the bent derralieur hanger theory. You can't whether or not if it's in alignment by just looking. The Park derralieur hanger alignment tool will take care of the checking and the alignment. Any decent shop can do it, or you could buy one for about $45. BTW, hangers are often and easily bent in crashes, if the bike is layed down on the derraileur side, transportation, etc.
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