Chain sits on top of chainring when shifting up

[Frankly]

(02-18-2014, 08:15 PM)so2002 Wrote:  Hey guys,

First post here. I've tried searching, but I don't know what you call this.

I have a vintage Schwinn Passage that I picked up a few months ago. At first it worked well, but recently it's been giving me trouble.

When I shift, the chain pops into the higher (larger) gear, but then sits on top of the chain ring. What ends up happening is that the chainring will keep turning, and eventually the chain will pop into place or pop right off.



I have replaced the rear derailleur, adjusted the F&R derailleurs, and just replaced the Chain because the last one was right at the edge of needing replacement. The problem still persists. I assume the fault has to be in the front derailleur or the chain ring.

Any idea of what is happening?

Mike

Those chainrings do not appear to be worn very much and the pitch of a chain does not change with number of speeds. What does change is the width of the chain so if you have an 8 speed setup and the guy you bought it from installed an 11 speed chain or a 12 speed chain, that odd error could conceivably occur. Likewise if you replaced the chain with a narrow chain the problem could continue. These days the chains they sell are for 8-9 and 10 speeds. But expensive bike shops might sell you a narrow chain unless you specify numbers of gears.

As for the front derailleur - it CAN cause that problem if misadjusted - for instance - if you're slightly overshifting from the small ring into the large ring. But it could should not do that from the large to small. Throwing the chain off suggests that The clearance (up and down) is incorrect and the outer limit screw is not set properly. The closest point that the front derailleur makes to the large ring should be about a quarter tooth high. New derailleurs usually have a see though plastic device that allows you to set the correct height. ``then pull it off and throw it away. But you have to make sure that IN the large chain ring, that the outer limit is set so that there is only enough room for the front derailleur to not rub on the chain. And the front derailleur should be almost parallel to the chain.

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(02-25-2014, 09:24 PM)cny-man Wrote:  It seems very odd that the first couple links feed on but then the following ones don't. The chainwheel teeth look pretty worn, even chewed up, but something else is probably being missed. Why not seek some in-person assistance - bike co-op, knowledgeable friend, etc?

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The chainwheel teeth look pretty worn, even chewed up, but something else is probably being missed. Why not seek some in-person assistance - bike co-op, knowledgeable friend, etc? I'm betting the right set of eyes and hands on the bike could figure this out in short order.

That wear on the sides if the teeth cam mean that the teeth are too wide for the chain. But the cups between the teeth do not look overly worn . So your problem is most likely the H limit not set high enough. But if you set it too loose it can overshift and throw the chain off of the high side.

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(02-25-2014, 05:04 PM)nfmisso Wrote:  

(02-25-2014, 05:00 PM)so2002 Wrote:  So, it's normal working condition, I just have to be more rough with it?

NO !!!

You need to adjust the H limit screw so that the cage can travel a little bit further. It has nothing to do with putting a lot of pressure on it.

Please READ.

I think that he probably has downtube shifters and so can force it into high gear but as soon as he releases the pressure the limit screw pushes the front derailleur back slightly. The front derailleur set up looks correct and he is using the correct chain (chainmakers are making 6-7-8-9-10 chains now). The chainring doesn't look worn so I'm sure you're correct.

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(02-25-2024, 07:28 AM)Biker2024 Wrote:  I had a similar thing to this issues

I adjusted and tuned the deraileurs in the front and back to a perfect clockwork, but still the chain derailed.

I did turn the front pedal slowly to see what happened. The funny thing it was derailing both to the outer side as the inner side and started dancing on top of the front chainring teeth.

So...

I was then looking at the chain from the above and first found there was a chain link that was twisted so it alway ended up on the outerside or on top of the teeth on the front chain ring.
I took two pliars and twisted the link back (Yes I am aware of everyone would say buy a new chain... I am opposed to this buy and throw mentality when you can repair!!).
Voila! the chain stopped derailing at the front.
The same thing was found on chain and a link when derailing on the inner side.

Look at the mechanic of the chain and chain ring. It will give you a big insight in where the problem is.

Twisted chain links are so rare it never occurred to me. But yes that could be a problem. Laying the chain on a flat surface and looking down it for a twisted link would reveal that.