Compact crank issue

[rayhuang]

First off-sorry for another compact crank thread, but this involves a weird issue that Ive never encountered before.

When in my 50/11 I cannot back peddle. As soons as I do, the chain comes off from the bottom of the chainring towards the outside. Luckily forward peddling brings it right back onto the chainring.

Could there be somethng wrong with the teeth on the chainring (I dont see anything, but the teeth have so many varied shapes, its hard to tell) or could it be the rear derailleur, the chain???

The bike is a CF Fuji team pro, 10 sp rear derailler is Dura ace, cranks are Truvativ GPX and shifters and chain are Ultegra 10sp.

all of it is new-only 400 or so miles on it.

Thanks in advance for any ideas,
Ray

 

[capwater]

Don't back pedal, seriously........

 

[rayhuang]

Don't back pedal, seriously........

So are you saying that this is an inherent problem with 10sp drivetrains or compact cranks or just not to backpedal because it poses the risk of taking the chain off?

I am NOT arguing., this is my first 10 sp drivetran and I want to know what I am dealing with here (manufacturers defect, set-up, etc.)!!!

 

[DiabloScott]

So are you saying that this is an inherent problem with 10sp drivetrains or compact cranks or just not to backpedal because it poses the risk of taking the chain off?

I am NOT arguing., this is my first 10 sp drivetran and I want to know what I am dealing with here (manufacturers defect, set-up, etc.)!!!

It's just a derailleur adjustment issue. Probably need to adjust the angle relative to the chainring, nothing specific to 10-speed. You should be able to backpedal slowly in any gear without throwing the chain.

 

[rayhuang]

It's just a derailleur adjustment issue. Probably need to adjust the angle relative to the chainring, nothing specific to 10-speed. You should be able to backpedal slowly in any gear without throwing the chain.

diablo-the problem is-the front derailleurs not touching the chain when this happens. The chains comng off from the bottom first. When I watch it-it gets lifted up and off a tooth so smoothly its like its meant to do that, which we know is not true.

Ray

 

[Retro Grouch]

diablo-the problem is-the front derailleurs not touching the chain when this happens. The chains comng off from the bottom first. When I watch it-it gets lifted up and off a tooth so smoothly its like its meant to do that, which we know is not true.

I agree with Diablo. I think that it's a REAR derailleur adjustment issue. If it happens to be bound up just a touch in that gear combination, the bottom chain run will go slack when you try to back pedal and the chain will come off the chainring.

 

[DiabloScott]

diablo-the problem is-the front derailleurs not touching the chain when this happens. The chains comng off from the bottom first. When I watch it-it gets lifted up and off a tooth so smoothly its like its meant to do that, which we know is not true.

Ray

AH - Well my main point stands, it shouldn't happen in the typical scenario of backpedalling a couple turns.

OK, other things it could be:
1. Rear derailleur hanger slightly bent or RD itself bent such that the idler pulley is outboard too far
2. Spacer problem or spindle length problem on the bottom bracket causing the chainring to be too far inboard
3. Chainring bent or warped.

 

[John M]

diablo-the problem is-the front derailleurs not touching the chain when this happens. The chains comng off from the bottom first. When I watch it-it gets lifted up and off a tooth so smoothly its like its meant to do that, which we know is not true.

Ray

Another vote agreeing with DS and Retro that it is likely a RD adjustment issue.

 

[rayhuang]

Another vote agreeing with DS and Retro that it is likely a RD adjustment issue.

Thank you to you all.

I will now add that gettng the rear derailleur to shift properly all the time has been an issue!! I think its hanging up because sometimes it will shift OK-then all of a sudden-it wont shift during a ride. Putting teflon lube on all moving surfaces as well as the guide on the BB seems to have alleveated that, but the chain coming off is still an issue. Mind you I still dont think it shifts crisp at all and I and my LBS have been fiddling with it for weeks.

Ray

 

[rayhuang]

Heres a quick picture of one of three teeth that appears to be causing the problem. One makes the chain go bump over the top and two will do what you see in this picture. Allthough I wont rule anything out, the culprit right now appears to be the chainring.

 

[gclark8]

Three things,
Measure the chainline.
Is the big ring a 10 speed? Check it physically!
Is the chain genuine 10 speed, check it also,
make sure it is fitted correctly, manufacturers mark up.

 

[kopride]

Heres a quick picture of one of three teeth that appears to be causing the problem. One makes the chain go bump over the top and two will do what you see in this picture. Allthough I wont rule anything out, the culprit right now appears to be the chainring.

There is a similar problem with the initial run of FSA cranksets. You are using a non shimano chainring with a shimano chain? and apparently the issue with FSA was with a variance between its chainring width and Shimano's chain width. The chain was tighter and the "push" off the tighter ring could cause the chain to drop. Apparently FSA has now corrected it by narrowing the ring slightly and I don't have a real problem with my newer FSA crankset, but Truvatix may have the same issue. Either that or the chainring itself is just defective, and you may have a few damaged teeth.

The typical issue with compact cranksets is usually dropping a chain on shifts between the large and small chainring (16 teeth difference versus 14 on a 39/53 setup) and the chain and chainring better work well together or you will drop it if there is a big push by the front derrailler

 

[rayhuang]

Everything appears to be kosher except the teeth that are causing the hopping/dropping are very close to one side of the chain when viewed form the top compared to other teeth. as a whole-the chainring appears to be running very true. I wonder if they are offset to aid in picking up the chain? Tomorrow I will attemp to contact truvativ as well as drop my bike off again at my lbs.

I also wonder if they did get damaged because my front derailleur was not well set by the lbs when brand new and a few times on rides I went for the big chainring and it wouldnt shift up and when it did finally get lifted up-it went with a crunch. Playing with the end stops of course fixed the problem and it shifts smoothly up and down now.

 

[kopride]

Everything appears to be kosher except the teeth that are causing the hopping/dropping are very close to one side of the chain when viewed form the top compared to other teeth. as a whole-the chainring appears to be running very true. I wonder if they are offset to aid in picking up the chain? Tomorrow I will attemp to contact truvativ as well as drop my bike off again at my lbs.

I also wonder if they did get damaged because my front derailleur was not well set by the lbs when brand new and a few times on rides I went for the big chainring and it wouldnt shift up and when it did finally get lifted up-it went with a crunch. Playing with the end stops of course fixed the problem and it shifts smoothly up and down now.

What did you find out??

 

[rayhuang]

What did you find out??

nothing yet. been so busy tryng to get ready for an out of town trip. I'll drop my bike off at the lbs before leaving town and first thing they said they will do is replace the chainring. If that doesnt fix it then I dont know yet.

Ray

 

[gclark8]

May I suggest a TA brand 10 speed big chain ring.

 

[Felt_Rider]

I had the same problem, but I got my bike back today for the front and rear derailleur adjustment and I hope that it will be good to go for tomorrow's ride. I have heard from others in my group ride that a certain LBS could get it adjusted right, whereas, the shop I purchased from told me they could do nothing about it.

 

[alfeng]

Heres a quick picture of one of three teeth that appears to be causing the problem. One makes the chain go bump over the top and two will do what you see in this picture. Allthough I wont rule anything out, the culprit right now appears to be the chainring.

Honestly, from the picture, it looks as though the ring is mounted inside-out ... but, I don't know how the ramps look on Truvativ rings.

Why does it look as though the ring bends inward?

 

[rayhuang]

hey guys,


Sorry for not updating this thread. My LBS which I bought the bike from is trying to get Fuji to send me new chainrings as the alignment all seems kosher on the frame, rear derailler and hanger. I can tell you that the drivetrain in the small chainring is getting louder and the teeth look awful for a new bike of only 500 miles. The chainrings are steel with chrome and in the spots that the chain comes off when backpeddling, the chrome is gone as is a some material as well. They look awful-like theyve been without lube and a chain made out of sandpaper. But of course its all being well maintained, cleaned and lubed by me.

anyways-this weekend my chain popped off both small and large chainrings while shifting. I havent played with derailleur adjustments lately to cause this. Crazy.

Very frustrating on a new $2200 bike. Worse I think my LBS owner is just swamped, understaffed in his little bike shop so its hard for him to be very active on this matter.

Ray

 

[rayhuang]

alright-I just got off the phone with SRAM. It was a funny conversation as the tech guy was talking like a well healed politician. I ask directly as he was "suggesting" that there is an easy solution, but it needed to be done between the LBS and SRAM, not through me the consumer.


Anyways I asked directly as I told him I needed to know whats going on with my bikes shifting "So are you saying there is a problem with these style chainrings?".

His answer was something like this and that was that Shimano often makes changes to there parts without telliing them and that makes there platforms they provide for the bikes incompatible. He also said they have a new chainring design that will help the shifting of my shimano drivtrain. He refused to give me a part number for them and kept saying-have your LBS call us. I told him its not that easy to just get my LBS to call.

Ray