Chain slap
 

I've got a bit of a problem with chain slap on my commuter. It's a 2010 Jamis Aurora Elite, with a Tiagra FD, and a Shimano Deore XT RD, and a SRAM 991 chain. It has a 50/39/30 on the front and an 11-32 on the rear. I recently had the drive train overhauled (new chain, new cassette, etc) at a LBS, but in less than 200 kilometers after getting the bike back, the chain broke on me while commuting in to work. I took the chain (sans bike) into the bike store to complain and they repaired it. I took the chain home and put it back on my bike using a SRAM PowerLink. After installing the chain on my bike, I re-oiled it. In the process of removing the excess oil from the chain (i.e holding a rag against the chain while moving the pedals in reverse) I noticed a lot of chain slap. To be clear, I found that the chain between the front derailler and the cassette (e.g. top chain) was becoming extremely slack and slapping against the chainstay). I initially thought that this may be due to my wiping up excess oil causing too much drag against the chain, so that the cassette wasn't able to wind it up quickly enough. So I stopped holding the rag in place and continued to move the pedals in reverse- but the chain slap persisted. For sake of comparison, I tried moving the pedals on my other bike also in reverse at a much higher speed and observed no chain slap; however, in that case it is a 53/39 on the front and a 12-23 on the reverse and a 10 speed. Also note that there seems to be some rubbing between the FD and the chain, which makes me wonder if the LBS did a lousy job of adjusting the FD.

It seems like excessive chain slap to me, but what do I know. So my questions are 1) is this a potential problem? 2) How do I fix it?

Thanks,
Brad

Chain slap is very common. The small sprockets have the chain passing pretty low over the chainstay, so it doesn't take much for slap to happen. The only thing that prevents it upper loop chain tension when you pedal. However when you coast, the tension provided by the RD cage spring isn't enough to prevent slap, which is by design because more spring tension would increase power loss.

Don't worry about preventing slap, instead focus on managing it. I use a length of split vinyl tubing strapped to the chainstay at three points with tie wraps. It's not fancy but works well, not only protecting the chainstay (who cares anyway) but muffling the noise of impact very well.

Just to be sure we're on the same page, I'm not talking about the lower chain slapping; it's the upper chain, which goes through the FD, and it happens when I move the pedals in reverse. It's almost like the cassette can't keep up. I don't normally back pedal very often, and if/when I do, I don't normally do it quickly, but I've never noticed anything like this happening before on this bike. Given that the chain broke less than 200 kilometers after it and a brand new cassette were installed brand new by the LBS, I wonder if they've screwed something up and this is just another indication of mistakes.

Yes, we're on the same page. The tension in the upper loop is high when you're pedaling hard. Coasting it's equal to that of the lower loop, and when back pedaling it's equal to the lower loop less the resistance offered by the freehub.

If the upper loop sags significantly when you coast it means that there's excess drag in the freehub which is trying to push the chain forward, spooling slack into the upper loop. If it doesn't sag coasting, but does when backpedaling than the drag may be in the RD pulleys.

You can do a quick test of the freehub by removing the rear wheel, and spinning it forward in your hands. Put a finger against the cassette and it should take near zero force to stop and hold it. If the cassette feels like it wants to turn with the wheel, it may need to be serviced (cleaned and lubed). BTW- sticky freehubs are very common in bikes ridden in wet conditions.

Going back to your earlier post. I doubt this problem was caused by the shop, and was more likely something developing over time. It might be related to whatever caused you to replace the chain the first time though, and it's disappointing that the shop didn't notice. Even if the shop is 100% blameless you might consider taking your future work elsewhere. There's nothing worse than having to depend on a mechanic you don't have confidence in. It isn't about his skill, it's about your comfort.

I would check the jockey wheels for dirt and drag.

They mow the sides of the MUP's all the time and
I get grass clippings in mine from time to time.

Thanks for the input. I looked at the jockey wheel, and there seemed to be some dirt in there so I tried to clean it out. That helped a bit, but it's not perfect. On my ride in to work this morning, the chain slap was still there. With the chain still attached, I spun the rear wheel and it moved the pedals, I believe that's also an indicator that the free hub may need to be cleaned and lubed too.

At what point should I worry about getting the free hub serviced? I live in the Pacific Northwest, where it is pretty wet and the roads can get pretty gritty with run off from the hills.

Thanks!
Brad

if the freehub is pushing the chain forward when you coast, I'd service it at my first convenience. It isn't critical, but could be an indicator of rust starting. Cleaning and oiling sooner can save you a costly replacement later. Ride it as it is, but don't put it off forever.

Your freehub 's servicing time depend on a lot of things, like how much time riding in bad weather , or dirt and dust . For myself I service my once a year . Try flushing your freehub with something like WD-40 then re-lube it with something like TRIFLOW or another light oil . Spin the freehub as you put in the oil and the WD-40 .

I've never serviced a freehub before, so I'll go and look for a youtube video and I'll get that done this weekend. I'll also have to buy some WD-40 and some Triflow oil- I have chain oil, but I need to buy some more of that anyway.

On the topic of rust- this bike has a steel frame (Reynolds 631). It fell over in my garage a few months ago and dinged the top tube. I've been advised that it isn't structural, so I don't need to replace the frame, but I noticed this morning that there is some rust starting where the paint was broken. Any suggestions? The options I've been contemplating are covering it with clear nail polish, but I'm not sure if that's the best approach. There is a local frame builder that I can take it to, and he said he'd take the ding out (fill it with brass), prime and repaint the affected it for me- I think he said it'd cost between $150 - $250. Another option he gave me was to take out the ding, fill in and fix other dings and dents (if they exist), strip the old paint off the whole bike, and repaint the bike in my colour of choice (about $450 all in). I'm not sure if that price included reassembling the bike or not. At $450 it seemed like it might make just as much sense to ride the bike until it became a problem and then just replace the frame with a new one, but I could also get a custom paint job that way (I'd probably go barbeque black if available).

I really appreciate your help guys.
Brad

Chain slap: Based on what's above, it sounds like a sluggish freehub is the culprit. I'd clean and relube it. It's not difficult if you've serviced cup-and-cone bearings before. A chain that's too long can also make chain slap excessive combined with a weak RD spring. I know you didn't install the chain, but if you ever take it off check it with the big/big +1 method: http://sheldonbrown.com/derailer-adjustment.html#chain

Frame rust: a small spot I wouldn't worry about. It's just a surface ding, they don't usually get worse over time. I have frames that are 30-40 years old and covered in rust that are completely fine. Except cosmetically of course...

for rust ,just sanded the area and touch up with paint . as far the paint goes any fingernail polish will be fine or go to a hobby shop and pick up some model paint . they all come in many colors so one should match . For servicing the freehub you'll need a chainwhip tool and a cassette locking tool to remove the cassette from the body . Cost of the tools around 25 - 30 at your LBS .

Thanks for the info. I've never done any work on any of my bikes before, and I don't have the tools either. I'm not against doing it, and I'm at least somewhat mechanically inclined. I'll try and find some youtube videos of how to do it before deciding if I will try it. I don't think the chain is too long- when I re-installed the chain last night, it didn't seem like I had excess slack. The system seems pretty tight when it's on the big chain ring and the largest cog- I think it is the freehub.

By the way, not that I've been to Oshkosh, but I love Wisconsin! (Okay, maybe not as much as Minnesota, but still).

Thanks, I'll do that. I am somewhat bothered by the ding and the marked up paint. I've got between $250 and $500 of fun money to spend in the next few months. I was debating spending it on repairing a headphone amplifier I built (but never got fully working) and buying a set of bib shorts, a road bike style helmet, and a jersey (I don't have any of those things, I use running tights, an old MTB style helmet, and a running shirt)- but getting the frame stripped, repaired, and repainted for $400-$450 sounds somewhat interesting to me. I don't know why- this is essentially my commuter / winter bike, but it's also my first road bike and I really love it. I'd get the frame repainted in matte barbeque black with silver accents. It's totally unnecessary, but it appeals to me. Common sense will probably get the better of me, and I won't do it- but I'd like to.

we all been there and know where you are coming from . to paint or not to paint ? that is the question and only you are the one who know.

Sounds like you have the itch to paint something. Rather than repainting your frame with one ding, I'd find a bike in poor/rusty shape and go nuts. Strip it and spray paint it yourself. Just make sure the frame will fit you, then it will be a fun project to paint and rebuilt. When all is done you'll have another bike! Nothing wrong with that.

Minnesota? How many Super Bowl wins do the Vikings have again?? :)