# Help! New chain "slips" on front chainring!



## Oxtone (Jul 13, 2005)

Help!

I just had my old Trek 400T bike overhauled at a good shop in town. They replaced my
rear Freewheel, and installed a new Chain. 

After I picked it up, on a ride the chain came off near the spokes, and sliced through six spokes like butter! The shop re-built my rear wheel for free, and adjusted the Derailer. 

Since then the chain keeps slipping, but now I think it's slipping on the middle *front*
Chainring, which I use most of the time. The three front chainrings were not replaced in the overhaul. This usually happens *when I apply torque **on the drivetrain after stopping*. This is really frustrating, and I'm afraid to get up out of the saddle to climb a hill with the chain slipping like that. I didn't have this problem ever before in the 15+ years I've been riding the bike. I use Crank Bros pedals and Sidi shoes. 

*Any idea's what the fix might be?* I looked at the teeth on the middle ring, and I don't see any broken teeth.


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## C-40 (Feb 4, 2004)

*simple...*

Look for worn teetn on the middle ring. They will become quite pointed (sharkfin), compared to new ones and the space between the teeth becomes much wider and dished out. A new chainring is probably the solution.

Worn chainring teeth are more likely to cause chain suck rather than skipping, but I'll bet it's just a worn ring.

http://www.fagan.co.za/Bikes/Csuck/


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## RMXCKSU (May 15, 2007)

How old/many miles are on those chainrings? I'd have to think your middle ring is a bit worn. My perspective is comes from the fact that my mountain bike suffered the same ailment once upon a time. I was certain it couldn't be that since I didn't think I rode in that ring that often but upon close inspection with a shop, it was obvious. I understand the reluctance to stand on it and crank.

Check those rings...


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## slidecontrol (Feb 18, 2007)

oxtone, i have had the exact same symptom on my last bike, the only fix is replace the ring.

i used a tiagra ring as the replacement ( I rode in the middle ring lots too) th tiagra is a tad heavier, but it is made of steel, and will last for almost ever.

middle rings wear faster because of the ramping required to make it shift in two directions, thus leaving a reduced tooth shape to absorb the chain forces.


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## Oxtone (Jul 13, 2005)

All,

Thanks for your help. I think I will replace the middle ring, if not all three. They are 
pretty old rings, and have thousands of miles on them, but mostly the middle ring. 
But, I didn't have this problem with the old chain and freewheel until both were replaced
recently during the overhaul. 

I suppose a new chain just doesn't mesh well with the old, worn chainrings. I haven't had it slip on the smallest or largest ring, but just the middle which I use the most. 

So, I'll see how the replacement of at least the middle ring does.


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## Oxtone (Jul 13, 2005)

C-40 said:


> Look for worn teetn on the middle ring. They will become quite pointed (sharkfin), compared to new ones and the space between the teeth becomes much wider and dished out. A new chainring is probably the solution.
> 
> Worn chainring teeth are more likely to cause chain suck rather than skipping, but I'll bet it's just a worn ring.
> 
> http://www.fagan.co.za/Bikes/Csuck/


C-40,

Well, I just discovered the obvious! I closely inspected the front Chainrings, and sure enough, *the middle ring teeth look just like Sharks Teeth*! Most are very pointed, and I found at least one tooth that was shorter than the others. Compared to my small and large rings, the teeth on the middle ring are very small. Now the question: should I just replace the middle ring, or just get it over with and replace the entire Crankset? I called the shop that did the Overhaul, and they said a whole new Crankset would run around $100.00 and replacing just the middle ring would run about $30.00. The mechanic said since they did the Overhaul, and missed this problem, that he would wave the labor charge for this. I think I'll bring the Bike down tomorrow and discuss the fix with them.


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## Oxtone (Jul 13, 2005)

Well, I just got back from getting a new Sugino Triple Crank installed, and a new BB. I decided it was time to just replace the whole thing, and the previous Crank had thousands
of miles on it. 

I'll try it out this evening, and see how she works. Hopefully this will solve the Chain skipping issue.


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## Touch0Gray (May 29, 2003)

Oxtone said:


> Well, I just got back from getting a new Sugino Triple Crank installed, and a new BB. I decided it was time to just replace the whole thing, and the previous Crank had thousands
> of miles on it.
> 
> I'll try it out this evening, and see how she works. Hopefully this will solve the Chain skipping issue.


let us know....I'm curious


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## rochrunner (Jul 11, 2006)

Back in my motorcycling days, we always said to replace the chain and sprockets at the same time if both are worn because a worn sprocket could damage a new chain and vice versa.


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## iliveonnitro (Feb 19, 2006)

Theoretically, that is what you should do.

Also, watch out for the crappy FSA Gossamer crank/chainrings. Brand new they wouldn't grab onto the chain. Eventually the rings were switched to FSA Pros and a slightly wider chain was ordered.


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## Oxtone (Jul 13, 2005)

All,

Problem solved! Last night I put 20 miles on the Bike, and the new Triple Crank
and BB performed perfectly! The chain did not skip at all, and the whole new drive train
feels really solid. It's also very quiet, since it's adjusted very well right now. The middle chain ring has shifting ramps on the inside for smoother shifting, and it works very well. 

My new chainrings are two teeth smaller than what I had, but, so far, so good. 

So, thanks to all of you for your input - it is much appreciated!


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## Oldteen (Sep 7, 2005)

Oxtone said:


> C-40,
> 
> Well, I just discovered the obvious! I closely inspected the front Chainrings, and sure enough, *the middle ring teeth look just like Sharks Teeth*! Most are very pointed, and I found at least one tooth that was shorter than the others. Compared to my small and large rings, the teeth on the middle ring are very small. Now the question: should I just replace the middle ring, or just get it over with and replace the entire Crankset? I called the shop that did the Overhaul, and they said a whole new Crankset would run around $100.00 and replacing just the middle ring would run about $30.00. The mechanic said since they did the Overhaul, and missed this problem, that he would wave the labor charge for this. I think I'll bring the Bike down tomorrow and discuss the fix with them.


Sounds like an honest shop. Too many bike shops I know would have tried to hit you for another labor charge to swap the crankset.


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