Funktopus

Hi all. I recently bought a 54t chainring to replace my 52t ring. The seller described it as jn good condition, and on ebay it indeed looked good. Item listing here: https://www.ebay.es/itm/384031005089

However! With it installed on the bike it's been a nightmare. It won't shift easily at all. If I'm cycling on even a mild incline it either won't leave the big ring, or it will have serious chain suck and get the chain very tangled. Pic of the carnage:






I've adjusted the derailleur to no end. Taking a look at the teeth in person they actually seem pretty sharp. Can I get a sanity check on this? Is this chainring toast? Closeup of teeth:


With the derailleur I've found the original manual and followed the instructions to the letter. Nothing out of the ordinary, position 2-3mm above teeth, make sure the outer cage is parallel to the big ring. I've fiddled with the limit screws to make shifting more aggressive, but it was fine on my old chainring. The derailleur can take the jump between bug and small, it's a difference of 18t, which is fine with this Shimano 600 FD6207. Anything I've missed?

Thanks

rustymetal

If its slipping or jumping as you apply pressure, then its a chain/sprocket issue, but if its just derailing the chain, its an adjustment issue.
Those teeth don't look all that bad to me, or at least not bad enough to be jumping the chain. For the chain to get down on the BB like that its likely a derailleur adjustment issue.

Worn teeth generally start getting 'hooked' and the gaps start to oval out in one direction. They start to look like shark fins.
The chewed up tips on the teeth are from rough shifting or partial shifts where the chain didn't just jump to the next sprocket cleanly.

Funktopus

Thanks for the reply!
Everything's fine until I try to shift up front.
If I'm cycling on a flat or downhill it will shift relatively well up front, but if I try and shift on a slight incline it will either stay put until I'm flat again or throw it off the rings.
Not sure what else I can do for the derailleur. Had it set up with my old chainring fine. It shifts great in the stand, but nearly kills me in traffic. Are you thinking it's more likely derailleur angle or limit screws?

oneclick 

One thing to check is whether the teeth are slightly thicker than the space between the side-plates of the chain. If they are it can give the symptoms you describe.

This can happen if a new chainring is used with a worn chain; the teeth do not wear as they would have with a chain that was new and wore in concert with the chainring; instead the driving face of the teeth will creep sideways, resulting in a slightly thicker tooth. It's easy to tell with a fingertip, feel for a lip or upset edge on the leading face of the teeth. It's also easy to fix, a few minutes with a smooth or dead-smooth file.

It can also happen if you try to use a 1/8" wide ring with a chain meant for 3/32", though the chain-suck in that situation is almost always so bad that the combination is essentially unusable.

Funktopus

If I'm understanding you right, this looks ok:



The chain hasn't had a huge amount of wear, maybe a few hundred miles.

Looking at the derailleur again it might be ever so slightly askew. Will straighten it out.

pastorbobnlnh 

I don't know if this matters or not to your situation, but the pin (shown at the 10 o'clock position in your first picture) should be placed behind the crank arm. It prevents the chain in such conditions from becoming wedged between the chainring and the crank arm.

The pin also helps facilitate re-engaging the chain back onto the chainring if your FD pushes the chain outward too much. Usually when this happens a slight adjustment on the shifter will place the chain back on the chainring.

Have you tried moving the FD higher on the seat tube?

balto charlie

Chainring looks good but backwards as pastorbobnlnh stated.

pastorbobnlnh 

Not "backwards." The pin does need to face outward but is positioned behind the crank arm.

cudak888 

Agreed. That (Nevar or Stronglight?) chainring has a fairly aggressive tooth which is probably hanging up on the chain pins a bit too aggressively.

Bring the FD up to see if you can ease off on the angle that the chain gets passed onto the large ring at.

-Kurt

Bianchi84

I might be wrong, but in that last picture with chain on small ring, the extreme right seems to show chain not meshing with ring (?) I think I see a gap there. Or maybe it's just lifting up at that point so not wrapping around.

daverup 

A bigger ring than original should be accompanied by a new longer chain.

jadocs

The first thing you need to do is check to make sure your chain is the correct length. Although 52 to 54 doesn't sound like much, we don't know if your chain was borderline too short to begin with.

Ironfish653

+1

The 53t SR chainring on my '76 is like this. I have to have the FD cage about 8mm above the teeth to make it work correctly.
It's been commented on, and I've adjusted it down, but then it doesn't want to pick up the chain.

dddd

Check carefully for any bent chain links (viewed from above) or stiff link pivots (viewed from the side), either of which can cause slippage or downright unshipping of the chain off the sprocket.

The chainring teeth look about like new to me, I would not question their wear life.
But do check for any possibly bent tooth/teeth!

Bianchi84

Good point about stiff links; I know I've overlooked this myself sometimes. My best check is pedal backwards (off bike and observing). Stiff links will be obvious trying to get through RD.

thook

re: stiff links
particularly if you had to cut the chain vs using a quick link. i've had this happen when i pressed the chain back together and, later, had to back the connecting pin off a bit

balto charlie

Yes you're right, my bad. I feel stoopid

ThermionicScott 

I actually wonder if lowering the FD and limiting its outward travel might help. When the FD is too far away from the chainring, the extra distance allows the chain to snake over instead of shifting, sort of like an RD with a large chain gap.

I set up my FDs so that when the outer cage plate is directly over the chainring teeth (chain needs to be on the smaller ring or absent), the gap is as close to 1mm as I can get it, and the cage can only move far enough out to keep the chain from rubbing when in the smallest cog. This seems to help it shift faster when I want it to.

One other thing: when you're trying to shift to the small ring, which cog are you in? If you are in the smallest cogs, the chain angle is working against you -- it's better to have shifted to somewhere in the middle of the cassette first. Although, being in the largest cog also increases the risk that the FD will overshoot the small ring and dump the chain onto the bottom bracket shell. So it's a balance.

Funktopus

Thanks all, appreciate all the advice. Just had a chance to try some of it out, unfortunately not quite there... raising the FD seemed to fix the issue, until the chain started falling off both the large and small ring when shifting. This appears to be an issue that I should be able to solve with limiting screws, but both screws are already 100% tightened - and the DR is still travelling too far. Seems the only thing that can fix that is a different derailleur? In an attempt to stop that symptom I tried lowering the FD slightly, which. didn't fix the problem but did bring back the original issue of the chain not being able to shift under load. When I moved the FD back up the chain still wouldn't shift under load, so not sure what's happened there...

Thanks for explaining that - I had a feeling the pin was for catching the chain, didn't realise it was to specifically stop it from burrowing in beneath the crank.

I'll try this again tomorrow - it did seem this improved the situation for a brief while. It's a Stronglight btw!

Thanks - I've checked for bent links, they all seem above board. Would have been an easy fix!

I'll try this one tomorrow too. I did have the cage 2mm above the teeth, I'll bring it down to 1mm and see what happens. I can't limit the FD travel any further than I already am unfortunately though - something that's always bothered me about this derailleur. Might start looking for another.

Funktopus

Made a few changes this morning that seem to have fixed it.

1. Swapped the Shimano 600's limiting screws with some from a very battered old Sachs Huret FD I stripped from a Raleigh Eclipse. The difference is huge, the other limiting screws must have ground away from being tightened while the derailleur was at the wrong extreme. Can now get it exactly where it needs to be, which fixes the problem of it throwing off the chain.

2. Removed the chainring to put the pin behind the crank as Pastor Bob suggested. In the process of doing this found out one one the nuts had a strange washer around it that none of the others did. Washer was fused on! So had been there for some time:


As well as fused, the washer was split and warped, so potentially preventing a strong, solid attachment of the big ring. Replaced this with a nut from a crankset I'm not currently using.

Rode with the FD 8mm above the teeth and all was (mostly) well. Out of curiosity I put it back down to 2mm and the sucker once again wouldn't shift. Back up to ~6 or 7mm and we have achieved perfection.

Thanks all!

Johno59

Ehh...some of those teeth are definitely shark fin shaped. I hope the person you acquired it from gave you it for next to nothing.
The FD might be struggling because the links are being hooked to the top of the fins in a manner a straighter, less curved tooth would not constrain the chain being lifted by normal FD action

oneclick 

That washer isn't supposed to be there. It's split and warped on purpose, that is a so-called "lock washer".

It might have been put there if the person doing the putting did not have a tool to hold the nut from rotating.

Johno59

The chain-ring seat face on the individual spline arm determines where the chain-ring aligns. The fasteners are located on the outside. They would have to be stuck between the flat mounting surface on the spline and the chain-ring to put the chain-ring out of whack.

Johno59

The moral of the tale is ten cents worth of oil applied every week (the manufacturers recommend oiling daily!) reduces many of these problems. Shark fins indicate a worn chain eating a perfectly good chain-ring - a ten dollar chain eating a fifty dollar and up chain-ring. Some of the chain oil bath bicycles I've worked on have chains and crank-sets that are a hundred years old. They look brand new. The epicyclic ones have 150 ball-bearing in the 'BB' to lubricate as well - they also look new. Certainly they are made of much stronger materials ( the chains are impossible to break with a modern chain breaking tool) and the split link is literally bolted together but without constant lubricating oil they would not last much longer than modern components - leave alone a hundred years.