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Throwing my chain - Flexible Chainrings?
Last Post 01/26/2016 10:55 AM by 79 pmooney. 26 Replies.
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Jimmy

Posts:33

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01/11/2016 04:39 PM
I have a Wilier Zero.9 which has FSA SL-K compact cranks with a 50T big ring.  It's a FSA BB386 bottom bracket and a new chain.  Chain line appears to be correct and has also been checked by a mechanic.

When I go into a sprint at speed, and then wind up the power, I am fairly consistently throwing the chain over the top of the big ring.  As you might imagine, this is fairly disconcerting.  I am at speed, under very high load and I throw my chain.  It makes me not want to sprint, which is bad, because that's my primary area of strength. 

I used to race as a Cat 2, then Master's, and often won crit's.  The point being, I used to have a lot more power than I do now, and this has never happened before on a variety of other bikes.  This is my first time sprinting on a compact crank.  I just can't figure out what is going on.  My only thought is that the SL-K big ring is twisting.  But I have used FSA rings before with no problem.  I need help before I end up stacking it.  Thanks!
Nick A

Posts:525

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01/11/2016 05:33 PM
Assuming everything is adjusted correctly, as it sounds like it is, could it be flexibility in the frame?

When I was younger and stronger, back when they had stiff steel frames, but downtube friction shifters, if the shifter was a little loose, and you flexed the frame enough, you could change a gear in back.

N
ChinookPass

Posts:809

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01/11/2016 06:45 PM
Can you make it happen in a stationary trainer? Might be able to video it or have someone watch. In high-def, might be able to see what is flexing.

Thinking about throwing a chain in a sprint gives me the shivers.
Jimmy

Posts:33

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01/11/2016 09:47 PM
I can't seem to get it to happen on a trainer. I am not sure if its because the stress is different or simply because i don't have the same ramp up of torque and rpm as on the road. It could be the BB, but it's a pretty stout BB. And while not exactly a scientific measure, it's the same frame Marcotte won the crit championship on. And that boy generates some big numbers.

Thinking about throwing a chain in a sprint..a true sprint..gives me the shivers too. I snapped a crank doing an uphill sprint workout several years ago, and went down like a ton of bricks. So I am extra fearful. (Crank had to have been defective, not as impressive as it sounds,)
Cosmic Kid

Posts:2187

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01/11/2016 10:01 PM
I would doubt it is the CR....100bcd and a 50T is pretty stiff. Maybe I could see it happening if it was a 52T, but even then it would be a stretch.

My gut reaction was frame flex....and chance you have a crack somewhere?
Just say "NO!" to WCP!!!!
79pmooney

Posts:1759

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01/12/2016 12:27 AM
A trick I used to do when I ran the super quick shifting (for its era) Shimano Uniglide chain (circa 1978) was to narrow the FD stops until the chain just rubbed in the big front - small rear and small front - big rear combos. You might try that. I only used the Uniglide chain for big races, using the much longer lasting Sedis chains with my training wheels. In your case, you might try narrowing the stops only for races. If that works, perhaps you could document how much you need to tighten the stop screws (say 1/3 turn) then it would be a brain dead operation to tighten and return the stops. (And I know, brain dead both before and after a race is good because that was often where I was.)

Ben
Nick A

Posts:525

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01/12/2016 10:16 AM
Even though a mechanic checked it... there's up and down adjustment of the front derailleur. There's rotational adjustment, etc., there's a lot to tweak...

I've had slightly loose bottom brackets, slightly loose chain ring bolts, crank arms, rear hub cones, a little loose rear cassette, just weird stuff that isn't obvious at slow speeds or on a work stand, that present problems under more extreme conditions.

Could all be stuff you've checked, but just throwing it out there.

N

Nick A

Posts:525

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01/12/2016 10:19 AM
79,

I miss those Sedis chains. Lasted forever, and CHEAP. As a poor junior, I would clean and run them forever. Finally did break one, and was scary. Pre- cell phones. I walked in my cleats, and rolled down hills, in an aero tuck for the three or four miles home.

N
longslowdistance

Posts:1500

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01/12/2016 08:05 PM
I have little to offer to the OP other than I agree it sounds like a combination of frame flex and perhaps a slight derailleur misadjustment.
.
Sorry for the thread hijack. Anyone younger than 35 stop reading now. Really. I mean it. You kids get off my lawn!
Regarding the sedisport chains, I used to venerate them too. Cutting edge wonderfulness back in the day. I had one saved for many years and mounted it about a decade later on a (for then) more modern setup, perhaps an eight speed. Chain size had not changed. It sucked! The chain was too flexible.
Old school has its charms but what was cutting edge a few decades ago doesn't always mean much. Tech moves forward, and that's mostly very good.
79pmooney

Posts:1759

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01/12/2016 09:17 PM
lsd, those Sedis chains worked very well with SunTour Winners, Perfects, DTs and Cyclone derailleurs. The Uniglides were smoother shifting but the Sedis shifted well and qualified as race reliable needing little attention.

Now asking it to run smoothly over cogs the manufacturers had no conception of, well that could be asking a lot. Sort of like expecting the finest Weber carburetor back in the day to work in any car now. (And as I recall, the Sedis was oldschool 3/32" 5-speed. 8-speeds were two steps narrower.)

Ben
Nick A

Posts:525

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01/13/2016 02:06 PM
No! Nostalgia. Everything used to be better. HA!

One "new" thing that I really appreciate are sealed bearings. So nice to not have worry about that. Also, now that I live in the land of goat heads, clinchers that aren't terrible are nice to have.

Nick
Orange Crush

Posts:2017

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01/13/2016 06:21 PM
I am obviously a sprinting nitwit but trying to picture windiing up a sprint changing front ring particular on compact. I ride compact and even at modest speed I am in big ring, the small ring is for uphill and gravel clay trail.

Not that this solves anything, answers any Q's or fits in chain nostalgia cat so carry on.
longslowdistance

Posts:1500

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01/13/2016 08:34 PM
Any geezers remember the state of the art regina oro chains? If so, Would you admit that?
Ben, my memory is corrected - the sedisport from the vaults was on an appropriately spaced freewheel. What was awesome back in the day with friction shifters sucked with index shifters.
OC, thanks for that post. Made me smile through my dentures. (not really, just trying for a cheap laugh. Now you kids get off my lawn!)
I do hope the OP's problem is fixable with a screw turn and not a frame repair.
Jimmy

Posts:33

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01/14/2016 07:21 AM
No worries on hijacking the thread. I am old, too. Started with a six speed, remember 7sp SIS being a huge deal and poo-pood for the "click" alerting others to your likely.

I think I'll bring my bike in for a second opinion elsewhere. It's worth checking again. Thanks!
zootracer

Posts:577

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01/14/2016 11:43 AM
I had the same problem with a Campy 53/39, after I installed a new front der. Threw chain over big ring. Worked fine in garage but not on the road. Packed a screw driver with me and adjusted on a ride. Never had the problem again. Although my frame is pretty stiff (Colnago Master X-Light)...things work different when under load...
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