CoyDawg

When I shift from the smaller chain ring to the bigger the front deraileur rubs the crank arm. I have to stop, get off and push it in to stop the rub.

Is there an adjustment I can make so it doesn't get out of alignment when going from the smaller to bigger chain ring?

TIA

Crankycrank

Here you go. Sounds like just a "limit screw" and possibly a cable adjustment. Front Derailleur Adjustment | Park Tool

79pmooney

Sick joke here - the rub is only temporary. Won't tale long to wear a groove in either aluminum or carbon fiber cranks.

And seriously - you know you can adjust how far the derailleur cage moves outboard with the limit screw. There are two screws on the top or front of the FD, side by side, that limit how far the derailleur swings in and out. It isn't always obvious which screw does which. (Some derailleurs mark them with H (high) and L (low) but not all.) You can look at the derailleur from the rear and see a little arm that rocks when you move the cage in or out. The screw it hits when moved out is the one. Tighten it until the cage clears your crank.

You may now have issues getting the derailleur to shift to the big ring. If so, welcome to the world of front derailleurs! Report back here, with pictures if possible. In my bike shop days of a past millennium, we used to cal FDs bumblebees; that like bumblebees, they theoretically shouldn't work but somehow do. They are not a precise mechanism like almost everything else on the bike.

cyccommute 

Limit screw adjustment should be the very last thing done to solve problems…like before you throw it in the recycle bin last thing. Unless someone grabbed a screwdriver and started adjusting the limit screws as the first level of problem solving, limit screws never need adjusting.

It sounds like you could have a couple of issues. First, you shouldn’t have have to push the derailer in for any reason. That sounds like your cables are sticky. The spring on the derailer should enough strength to pull the derailer back to the end of the cable tension.

You can check the cable without removing it by shifting to the large chainring and then downshifting without pedaling. This releases cable tension and allows you to slip the cable out of the frame stop. Look and see if the cable is rusted or has any corrosion on it. You might run a bit of grease down the wire between your thumb and forefinger. Then slide the cable back into the stop.

Before you go grabbing that screwdriver, do another check first. Look at your derailer in the highest gear. “C” in the picture below illustrates how your front derailer should be aligned. The outer plate should be parallel to the chainwheel. If the derailer clamp is loose, it can allow the derailer to twist and cause the tail to hit the crank arm. If the arm is not aligned, loosen the clamp, and straighten it out. You only need to loosen the clamp enough to move the derailer. You don’t want it loose enough to move downward.

Crankycrank

Limit screws never need adjusting??? They can go out of adjustment for any number of reasons such as someone tried to do some misguided adjusting at some time. OP mentioned a problem that sounds like it could be the limit screw and he has the Park Tool tutorial to check everything else but let's not tell the OP that it will never go out of adjustment.

Trakhak

Funny that, although you say that limit screws "can go out of adjustment for any number of reasons," the only example you give of a front derailleur limit screw needing to be adjusted is precisely the example given in the post to which you responded.

Yes, for a particular combination of drive train parts, correctly set limit screws never need adjusting, unless one or more of those parts are replaced or damaged.

3alarmer 

.
...I find it ineffably sad, that the mechanical advice forum has degenerated to this extent. The first instinct in here now seems to be making declarative pronouncements on what should never be done, instead of asking a few simple questions to elicit more information, in order to provide a more helpful response, to someone who is a little less knowledgeable. I am reluctant to participate any more. The "my wrench is bigger than your wrench" trolls have won.

Enjoy.

ridelikeaturtle

It's why I only log in to bikeforums once every few weeks/months. Due to a lack of regulation, then moderators often siding with "deplorables", and finally realizing I was giving a lot more than I was getting back...

3alarmer 

.
...

79pmooney

If the crankset has been removed and reinstalled just touch more snugly and the FD was set up properly to begin with, the OP might see a rub; a rub that is quite properly fixed with just the limiting screw. Now, needing to push the cage in suggests another issue like cable/housing/lube but that's a separate issue in this case.

OP, I've had bikes where the FD cage and crank were very close. (The old cranksets had much straighter arms in the days when the outer FD cage plate was dead flat. Cages were narrower and it was expected you might have to play with FD shifter a touch to not rub the chain depending on the cog used in back. I seek out those cranksets for their very low Q-factors (the distance the pedals are apart). On some of those setups I have to live with rub as I shift on to the big ring. I then move the (downtube) shift lever forward touch to eliminate repeated rubbing. (Aluminum cranks and as I joked in my first post, the rub is lessening with usage. Yes, yes, all "wrong" but so much cheaper than replacement knees.)

shelbyfv

Maybe the mods could step in and remove posts that are irrelevant to this OP....

cxwrench

I think it's funny when people get super upset about the way others post. It's the internet, it'll never be 100% nice. Just deal with it, it's not like there's someone actually in your face being a dick. If it bothers someone that much just put the 'bad guy' on the ole ignore list.
ETA: I agree that if not touched by someone trying to be a mechanic limit screws will NEVER go out of adjustment by themselves. I will admit that there are some things that can happen that often end up in them being adjusted for the wrong reason.

cyccommute 

I can think of no situation where a crank that is undamaged would go on “more snugly” than the original installation. Even for square taper, there is a limit to how much the crank arm can slide onto the spindle. If someone over tightened (and damaged) the arm, that would change but just removing and reinstalling a crank will not change the location of the chainwheels.

I’ve removed and installed thousands of crank arms without needing to change the limit screw settings as long as the same crank is used.

cyrano138

Just another plus one on this post. Well said. There's no reason in the world this forum can't be a nice place -- other than that some people seem incapable of regulating their own behavior, and those are always the same people that will tell you that there's just nothing that can be done about it. Well, there is: don't be a dick.

For whatever it's worth, I don't think what cycocommute said was necessarily all that bad, and it did seem like a helpful response regardless of the tone, but the fact is there are at least a few people whose purpose in logging on to this forum just seems to be antagonistic. I know I've had a few respond to my questions that way.

Anyway, this guy's bike could be new to him and have come from someone who messed with the screws. Maybe while he was poking around he turned one a quarter turn not realizing what he'd done. And it doesn't seem hard to believe that if you were constantly banging on the derailleur or pushing it or trying to mess with it that you could have backed out a limit screw ever so slightly. There are plausible scenario wherein the limit screws are the first thing that need to be adjusted. Lord knows I've done it.

I'm not an experienced enough bike mechanic to be cocky or to have lost my sense of humility about the whole enterprise, but I am experienced in other things in my private life, and I find it helps to take three deep breaths and, above all, be nice.

cyccommute 

The person you are responding to and I have a “history”. He seems to assume that anything I post is wrong because I’m stupid.

Frankly, I don’t see a “tone” to what I posted. I’m really trying to save CoyDawg some hassle down the road by addressing the most likely issues before the least likely ones. In 10 years of co-op experience (and laying hands on north of 15,000 bikes), a large percentage of what I have to fix (actually refix) is due to some one thinking that those two screws on a derailer are meant to “fix” shifting problems. The vast majority of solutions to rubbing, jumping gears, bad shifting, etc. are due to cable issues. Close to zero are due to a misadjusted limit screw. And, in the instances where it was the limit screw, it was user caused.

Sorry but no amount of banging on a derailer is going to cause the limit screws to go out of adjustment. The screws in every derailer I’ve worked on have locking compound on them and/or are tight. They don’t rattle loose in thousands of miles of riding where the vibration is more likely to make them move than any amount of banging.

As for starting with limit screws to solve problems, the only time that it would be the first place to start is if someone told you that they had “adjusted” them. Even then, that’s on the operator because they started there.

I’m not being “cocky”. I’m trying to help and to share a lot of experience and I try to be nice about it. There are, of course, people who can get under my skin be even then I try to be civil and not fall into the trap of hurling insults.

JohnDThompson 

We have no reason to believe that the bike was properly set up in the first place. It could have come into the OP's possession with the limit screws set wrong, the outer cage plate misaligned, etc. Given the information we have, any of the previous responses could be appropriate.

cyrano138

For whatever it's worth, cyco, you seem helpful enough, and you've offered some helpful responses to some of my questions in the past.

The broader point I was trying to make was about the general tenor of maybe 5% of responses on this forum (in my experience).

The specific point of my comment is that we don't know what the situation is (op didn't offer too much info), and it seems less than constructive to be so self-assured about what the solution would be. The reason I say that is because I fixed the exact same issue on my wife's Peugeot (after installing a replacement front derailleur that didn't fit well), by adjusting the limit screw to keep it from rubbing the crank.

I haven't fixed 15,000 bikes so maybe it was a stupid thing to do, but the bike works fine now and that was a solution.

3alarmer 

...+1

3alarmer 

...not at all. I think you often mean well, but seem to often respond in a manner that is remarkably insecure.



...none of us knows enough to help the poor OP yet, with his issue. Which was my original point.



...this is where you continue to go astray, if your real purpose is assistance.

...again, not enough information, but nonetheless doubling down on the absolute.



...oh please, Stewart. Tell me again about the thousands of crank arms you have pulled and reinstalled at your co-op.

See, the idea that you might have pulled them to install a new or different sealed unit BB, with the resulting minor differences possible in crank position, because many of the spindle lengths and tapers are not standardized...well that never occurs to you. At least, not before you've dictated another absolute.

If you've ever worked in a paid position in the mechanical trades, I'd like to hear about it. Otherwise, I have plenty of experience riding herd on a bunch of volunteer mechanics on Saturdays, at the bike co-op here. I know that some of them I had to watch more closely than others. And I know what it is to do mechanical repairs for money...in an environment where "bringbacks" were logged and recorded. And if you got enough of them, someone spoke to you about it.


It's not asking too much to request that you temper your sharing of wisdom here with some humility. And to approach your responses in a manner that is not an attempt to remedy your own insecurities, by choosing someone else to single out for your absolute mechanical wisdom. You'd suffer less embarrassment in the long run, and it would make it easier to address the problems that people are asking about. Try to think of it as playing for the team, instead of swinging for the fences.

Andrew R Stewart 

"...oh please, Stewart" 3alarmer

Miss spelling Stuart's name on purpose? I hope it's not a reach out to me, for whatever reason). At least both of us bother to sing off with our real names.

To the OP's questions. Limit screws can become loose for a few reasons. Other then a reason that has a screw driver in their hand, the loosening will generally take some time and shoddy maintenance. Low grade hardware, poor thread cutting in the der body, missing nylok or thread locking compound all are valid happenings. I've even seen rocks and such picked up by the tire to whack the der. The other rarely mentioned reason that limit screws might need readjusting from the correct first set up is that the contact points on the der links, that the screws get pressed against, can wear and some small impression can result. But in general I agree that with a well adjusted front der any future limit screw adjustments will be very small if at all, excepting incidents.

My own experiences suggest that cage condition is a common cause of poor shifting. I've seen so many ft ders with a bent cage that checking cage realignment before further adjustments is part of my approach. The cage can be twisted/bent up in it's tail from a pant leg. The outer plate can be bent outward and up in the front from jamming an upshift and the chain acts as the pry tool. These days cages are usually well sculpted with shapes to help lift/push/clear the chain as needed. But the cheaper units and all the old examples (usually with the over used words "classic" "vintage") of my youth had cages with straight/flat plates. We often would bent in the front ends of the cage to better move the chain and then catch the chain from going too far. So checking the cage's condition is in my blood.

Besides cable friction there's also the der pivots that can bind up. Here in the rust belt we see more then a few ft ders that are frozen from corrosion, road salt and/or sweat and put away wet. I have to say that cable friction is far less an issue with bikes that don't have a section of housing curving around the BB, and acting like a catch basin for water dripping down the exposed inner cable. Bikes that get left out in the elements will sometimes even show corrosion inside the housing leading to the levers.

I also agree that we would need more info on the OP's bike to do more then talk generalities. Andy.

3alarmer 

...spelling critiques are now fair game in the mechanics forum ? O tempora, o mores !!
If you are singing your name, though, every time you post in here, I approve.

3alarmer 

.
...we could use more singing in the mechanics forum. More singing would eventually lead to less bickering. Except for the inevitable critiques over quality and choice of material. Everyone's a critic.

cyccommute 

How is my post “insecure”? That word you are using doesn’t mean what you think it means.

No, we can’t know exactly what the problem is because we don’t have the bike in front of us. That’s why I named a number of options starting from most likely to least likely based on my years of experience. You, on the other hand, have offered nothing other than trying to troll me…to which I seemed to have risen again. Shame on me for that.

Again, I at least offered something rather than just toss bombs. Do you have experience that shows banging on derailers can cause the limit screws to unscrew? Or that they will unscrew from road vibration which is far more likely…but still very unlikely…than “banging on the derailer”?

Please try to keep up. That response was to another poster and not in response to CoyDawg’s post. As for the “absolute”, do you start with the limit screws when addressing shifting problems? Unless someone else “adjusted” them, there is never a reason to do an adjustment after set up to fix a shifting problem.

So I’m a liar?

Again, try to keep up. I was not talking about replacing a bottom bracket. Pulling a crank off the bottom bracket and reinstalling it on the same bottom bracket won’t result in any change in position of the crank unless the arms are way over tightened. And that only applies to tapered bottom brackets.

I know you think I’m a liar but I really have worked for 10 years at my local co-op doing exactly what you describe. If I have volunteers, I ride herd on them as well as paying attention to 6 repair stations. We limit stand time to 90 minutes at a time and our stands are filled every hour of every shift all year long. If everyone takes 90 minutes (which they don’t) that 24 clients per Saturday but we often run closer to 30 per shift. We often don’t have any volunteers and I’m the only person working the shop. At the end of any given Saturday, I hate my name because I hear it so much.


No one has had to “speak to me” about the quality of my repairs because I’m the one who checks the other volunteers’ work. The paid mechanics at the co-op often consult with me because they are unfamiliar with a bit of old tech. I know you think I’m an incompetent boob but they trust me enough to allow me to teach wheel building and the 6 week Master Mechanic’s class about 6 times per year (do the math). Not only do they allow me to teach the class but I redesigned the curriculum and developed a very comprehensive series of handouts that the other classes also use (we have 3 classes running at the same time). These are classes that people actually pay for (about $250 a student).

Perhaps you should follow your own advice. I’m not embarrassed. I stand behind my responses and even put my very own name to them. See the sig line down below? That’s my name. I stand behind it and don’t hide in anonymity. I also offer advice as opposed to just come here to cast aspersions.

Where have you posted any advice to CoyDawg on his problem? All you’ve done is to drag this thread into your own twisted vendetta against me. You’ve done far more to degenerate the mechanical advice forum than I have ever done. How about doing something productive for a change rather then just chase me around telling me (and everyone) how much of a stupid liar I am?

shelbyfv

Seems as if your post #7 was the one that derailed this thread. Not sure why you are posting in "Mechanics" anyway.

3alarmer 

... not sure how I managed to attract your attention, but probably when I mentioned that the trolls were winning, you thought "All right !!"
Glad to see your suggestion about removing stuff. Maybe someone can work on getting rid of the elephant in the room.