Bicycle Mechanics - chain"suck" ?(similar to thread below on chain catching)

(I meant to post this as a reply under dave 's topic of similar name but as I see I didn't I'll leave it as a seperate but similar ,I think ,topic)I think my bike has this same problem if you are talking about the rear derailler getting pulled up loosening the tension and causing a frustrating loss of leverage of the gear.For me this happens primarily in the upper front chainring particularly when mashing the gear hard.I have been just avoiding this chainring but recently noticed it start on the lower front ring though it seemed to correct itself as I rode and not come back yet.So are you all saying this is chain "suck" caused by concave teeth on the chainring and if so will filing them help?Or am I talking about something entirely different and if so any ideas on this?

Does anyone have any idea what the problemI described above is?On a ride today it seems to be getting worse in the lower chainring now.

So the chain tends to slip/skip/suck/misbehave when you apply a lot of pressure at the pedals... perhaps your chainring teeth have worn down to the point where the chain is slipping centrifugally all the way around at the same time. I've had this happen with worn-out middle chainrings on my mountain bike, and it is a recipe for cut knees and bruised, um, body parts. If you happen to be blessed with a digital camera, could you post a close-up photograph of your chainrings? Or ask a trustworthy LBS for an opinion.

Another possible reason for slipping under power is that your chain is at a different stage of wear than the rest of your drivetrain (cogs and/or chainrings, particularly cogs).

If it is actually chain suck happening under power, where the chain clings to the chainring and won't come off cleanly at the bottom, then this could be caused by burrs on the teeth or bent teeth. If you decide to replace chainrings, I strongly recommend aftermarket 7075 aluminum ones, and my favorites are Real's "Ultimate" ones. The aluminum is very hard, very strong, and nickel-plated. These things are worth the money!

Also, can you post more info on your bike? Could help... :)

It is a mid 80's Fuji Royale sport tourer with original parts except a fairly cheap rear derailler recently put on .I don't know for a fact it is a chain problem(or front derailler) as what I notice is the rear derailer sliding up(and then back into place) causing the chain to monentarily loose proper tension and creating kind of a "miss"as far as the gear leverage is concerned .The rear derailler is shimano and the other parts are suntour if this helps.I inspected the front chainring teeth and while i'm sure somewhat worn I noticed no obvious "sharks tooth" or concave pattern.

Hmm, try shifting the chain to the smallest rear cog and rotating the cranks backwards. Could just be a stiff link in the chain. If so, it'll probably make the derailleur jump noticably as it goes backwards around the cog and through the derailleur cage. If so, many chain tools have a secondary position intended to eliminate stiff links.

http://www.parktool.com/images/TTOL/chain-tightlink.jpg

http://www.parktool.com/repair_help/FAQtchan.shtml <-- How to fix :)

........

Yes I just tried that and the rear derailler was significantly being pulled foward less than every chain rotation.What are you saying about the chain tool as thats something I dont have now but have been meaning to get. this has been happening for a while on the upper front chainring but just started on the lower front the other day after a heavy rain which I rode through .Do you think a good lube to loosen the chain might solve the problem?

Thanks for the link .For some reason I didn't see that first time I read your post.I will look into that thouroughly tomorrow.

For information on both 1-ring and 2-ring suck, see
Chain-Suck in a NUTSHELL (http://www.fagan.co.za/Bikes/Csuck/) for :
- causes and mechanisms
- how to avoid and remedy
http://www.fagan.co.za/Bikes/Csuck/chain-tri-icn2.gif

Can this also be because of a "stretched" chain? I was riding along, shifted up top on the the front deraileur, and the chain came off and got stuck. I back pedalled a bit, and dislodged the chain, but ever since the chain seems to be hopping. I looked at the chain, and it's either an optical illusion or the chain seems to be twisted in the spanse between the front and rear gearing.

Oh, by the way... the Rear Deraileur was recently replaced, as the old one was torqued... but the chain was not replaced to my knowledge. I had a bike shop repair it, and am still quite new at bike mechanics.

Sounds like you have exactly what you described... a twisted chain. Usually the twist is localized and your LBS can replace just the pair of links involved... run it by them, if you're not quite ready to tackle it yourself, or pick up the small-sized Park Tool chain tool and refer to their instructions at their site (linked up above). Your LBS can probably sell you replacement links; they usually have plenty of leftover bits of all the common types.