Elric

So, I've been experiencing chronic chain loss on my 2007 Orbea Onix TDF and no matter what I try or what any LBS mechanics do, it just can't seem to stay fixed for more than a few hundred miles. I've had this problem for almost the entire time I've owned the bike, about 5000 miles now. The chain drops when I shift from the big ring to the small; this happens when I'm not in the biggest cog, and it happens whether I'm climbing, coasting, or pedaling easily on the flats. I have an FSA SLK compact double crank (50-34) with an Ultegra FD clamp-on. The cassette is a 105 12-25 10 speed, and the rest of the drivetrain is Ultegra.

I've been talking to as many bike mechanics as I can, and two courses of action seem the most recommended. The first is to get a chain drop guard, aka a dog tooth. The problem with this is that the lug around the BB on my Onix is too thick and makes it impossible to mount the chain guard where it would fit on just about any other frame. Do any of you know of any chain guards that might be specific to Orbeas or at least fit around a really thick BB area?

The second thing some mechanics have said is that the front derailleur might not be the right kind for a compact crank. Apparently Shimano says their FDs will work properly with both standard and compact doubles but many people seem to believe otherwise. I've searched on some of the online retailers but can't find any compact-specific FDs made by Shimano. Do any of you know about this?

I'd appreciate any light anyone could shed on this. I was able to live with this problem before but recently the chain dropped during a race and I ended up causing a mini crash, so it's something I really want to get solved as soon as I can.

Thanks for your help!

sfrider 

Your chain might be too short. What happens is if you're on the big cog(s) back and front it gets harder for the derailer to move the chain off the big ring, and it tends to come off with more snap. The pulley and cross chain in effect helps pull the chain inwards and the derailer gives, letting it come off the small ring. Even if the derailer can prevent it, chances are if it's not clamped on really tight that that over time this chain snap will cause it to rotate inwards. (Tail pointing towards frame rather than close to parallel.) It might not be enough to eyeball though. You might also have grit in the pulley, adding to the tension, making the chain come off the big ring with more force.

KevinF

I used a regular front derailleur (i.e., one meant for a 53/39) with my compact crankset for a while, and it worked well. The derailleur did have to be positioned carefully -- i.e, very little clearance (one penny width) between the bottom of the derailleur cage and the top of the big chainring.

Retro Grouch 

I've encountered that problem a couple of times before. When I've run into it the cause was a high limit screw that was set too close causing the derailleur to bind on the big ring. 1/8 turn CCW on the high limit screw was all that it took to fix it.

Elric

Thanks for all the suggestions, guys, I'll try them all out. Upon further discussion with people, it seems that the problems I'm encountering come with compact cranks in general and there's really no silver bullet solution to any of them. I guess when I get stronger I'll move up to a regular double.

Cheers

bucketheadmn

I have been riding a compact crank on my 2008 Onix TDF with the Ultegra SL 50/34 crank. First couple of rides I threw the chain inside going from big ring to small. Stopped at lbs and they made a quick adjustment and over the last 500 miles I have not thrown the chain a single time. My point here is that I would not lump all compact cranks into the same category as there are a lot of people riding one without any problems.