bokes

First off, I have a Surly XCheck which is not made for a triple crank, yet i want really low gearing, so I put a triple on anyway and i'm only using the small and middle rings. With that i'm using a double front derailleur. (a triple derailleur wouldn't work, cage was too long and would bang into the chain stay)

I've had 2 bike shops adjust the derailleur the best they could. Yet when shifting to the smaller ring, it falls off once every 20 shifts (shifting from the small ring to middle works flawlessly). I'm guessing this is not normal, because i don't see Tour de France racers getting off their bikes several times to place the chain back on the rings!

Actually, I have 2 questions:
1) What should one expect, a chain falling off once per 500 shifts? Once per 5000 shifts?

2) Should I get a frame made to take a triple? (And no, please don't tell me to get stronger and go to a compact crank! - have a bad back)

thanks in advance

MrCjolsen

It should never fall off if it's properly adjusted and any frame should work with a triple.

I have a Surly Crosscheck and it works fine with a triple. I'm using a Tiagra front derailleur with a 48-36-26 crankset.

Front derailleurs are spec'd to work with specific ranges of crankset sizes. And they are very touchy to adjust. Not just the derailleur but also the height and angle. But a bike shop should know this, so I think that you need to try a third shop.

Bill Kapaun

Examine your chain for any stiff links. If they don't pivot easily, they could be trying to "run off into space" instead of dropping on the small ring. Lubing the chain might help?

What happens if you turn the L Limit screw in about 1/32 turn? IF it still shifts OK to the small ring, try repeating.....back off when it doesn't.

I probably drop my chain about once a month? Rare enough that it suprises me when it happens. When I first got this bike it had a lot of stiff links because the DRs were so maladjusted, it would throw the chain every direction (front & back) except into the spokes (thank God!) It had been jammed so many times, I probably didn't have a run of chain longer than 6 links before it had a stiff one. It was actually too long, so I was able to remove about3 of the worst offending linksets and with some side bending and working them back & forth, get the rest "functional".
From Sheldons pages-
" The easiest way to spot stiff/damaged links is to shift the bike into the small/small gear (the gear you should never actually ride in.) This gear has the chain at its slackest, and flexes it farther than any other gear, as it goes around the small rear sprocket and the derailer pulleys. Slowly backpedal while watching the chain as it feeds through the rear derailer, and you will usually be able to see the bad link jump."

BTW, what's the size differnce between the 2 smaller rings. Anything out of the ordinary.

captainnemo

The problem with the crosscheck frame shows up with smaller ratio 44/32/22 cranks

see my post which sank without trace

https://www.bikeforums.net/showthread...ght=crosscheck

I should have the xt der by monday( have a shop/there you go third shop ) and will let you know if this works otherwise the above option of the 48-36-26 might be the only solution as it lifts the der mech away from the chainstay. The problem with this is you lose the very low gearing you are chasing.

You could also try the sram dual drive hub system with compact on the front which would give really low gearing ( it would be a shame to give up a crosscheck )

Retro Grouch 

Quick, dirty answer is a "Third Eye Chain Watcher" or similar product. It's a $10.00 plastic gizmo that attaches to your seat post and positively prevents the chain from overshooting the granny.

captainnemo

Ok update to my previous post.

To answer neither of your questions Bokes, get a FD-M761 FRONT DERAILLEUR XT HI-CLAMP 63-66
Installed one today on my Crosscheck and clears the chainstay comfortably and shifts perfectly. Much cheaper than a new frame and if you also follow retrogrouch's advice the answer to your first question is never.

Just checked Shimano's online system and you can also get it at LX level.

bokes

thanks for your thoughts folks, and RetroGrouch i'm going to get that gizmo. great suggestion.