issue with new inner ring on ultegra hollowtech

[willcee]

Mate had been having issues with his best machine he said theres a quarter of my inner chainwheel missing, not undestanding quite what he meant missing , and yes it was missing along with the two posidrive bolt fasteners.. he had issues with gears for some months so put it in the shed and used his winter machine , so he just commutes presently.. i had it back here and removed the cranks, 2 missing bolts and a 1/4 of the 34 ring gone broken out, i had a virtually unused one on my whyte E machine a 34 when i could have used 36 seeing it had an Orbea gain hub rear motor wheel so i pulled the cranks on mine and unscrewed the 34 ring it was immaculate called him said it would be ready after tea and duly fitted it on his machine, put bike on the stand and checked the gears faultless or so i thought.. few days later i called with him at work, hows the machine i asked, needs sorted, its dropping the chain between the rings not going onto the inner ring at all, we held her up he worked the gears i did the pedalling and sure enough it hung on the 34 teeth not going right over them at all, worked on the stand i says i'll have another look, that evening i started to consider what could have gone awry, and considered the ring may have one way of being fitted so perhaps in my haste i fitted it ass backwards.. anyone.. i feel a total idiot its a stupid mistake given my experience... will

[Cyclothesist]

Did you fit it the wrong side out or was that it was a different make of chainring from the outer ring and didn't sit quite right? I'm interested because I have a similar issue with an FSA triple crankset where I replaced the middle and granny rings with Spa zicral ones. Granny to middle is fine but just occasionally the chain will sit between the 50T outer and the 39T middle. I wondered if I'd fitted the new rings wrong side out but I hadn't. The recessed slots for the chainring bolts only go one way. The FSA 50T and the zicral 39T just aren't designed to be together. Maybe your friend's bike has the same issue?

[willcee]

They're definitely same make, both Shimano Ultegra, the 4 bolt type..and same colour that shiny blackish shade...Ii'm amazed so far that no-one except yourself has come out to say anything.. I was in fact waiting to get a ribbing over a silly error... will..

[andy74]

It's obviously an easy mistake to make, as I've just had one of the ladies in our club's bike in my stand with a similar issue. Chainrings had been replaced by a cycle mechanic. I found that the inner 34 ring had been fitted the wrong way around with the small counter bores for the chainring bolts facing the outer chainring. It's the slightest of differences in the offset, but enough for the chain to drop between the two. I'd chalk it up to experience and move on.

I'm a trendy consumer. Just look at my SM-S901B using hovercraft full of eels.

[Brucey]

if the chainring in question has counterbores for the bolt heads you are unlikely to have fitted it the wrong way round, I'd have said. However, if it is really an 8s chainring and the chain is 9s or higher then it could get stuck as described. The other possibility is that the chain is damaged, so it'll run OK on a worn big ring, but not a new small one.

Another poster reports problems with the middle ring on a tripe. If the chain 'rides' as described it only needs to do it once, under load, before it has carved itself a shoulder to sit on, and once it has done that, it usually gets worse and worse. However, there are only a few possible causes including:

1) no part of the correct big ring overhangs the spider arms, but the chain is somehow always thrown far enough by the correct ring for the chain always to mesh with the middle ring

2) the spider arms are slightly thicker than they should be.
3) the chain isn't really wide enough externally.(eg it is really a 9s ring/chainset and you are using 11s chain).

It may be possible to recover the situation in one of three ways:

1) make the spider arms slightly thinner.
2) file or reshape the tooth tops on the middle ring to a more favourable chamfer.
3) make some special spacers that sit between the spider arms and one or other of the chainrings, to function as a guide.

If contemplating the last of these, I would suggest that suitable spacers could be made using an old coke can, provided you can make half-reasonable 10mm holes in it. The procedure would first to cut strips about 14mm wide using ordinary scissors. Next, use something to make nice holes at least 10mm diameter near one end of each strip (tip; you may be able to 'cut/nibble' suitable holes using a good paper hole punch). Finally, you can fit the spacers in position, folding the plain end of each strip over so that there are additionally 1,2,3 or 4 layers above the middle ring/spider, but the chain is unlikely to get held up by the folded shim. In this way it ought to be possible to consistently direct even a narrow chain onto the middle ring.

Come to think of it, suitable guides could also be made easily, using epoxy resin/thread and given a metal facing if required.. The thread could be used to help 'bind' the epoxy resin in place provided the thread is applied whilst the glue is wet and there are suitable cutouts in the 50t ring.

[peterb]

I had a problem with the inner ring of a Campag Veloce 34/50 10 speed chainset where on dropping from outer to inner ring the chain would sometimes skate on top of the teeth of the inner ring, resulting in no traction and spinning pedals. After much searching on line and visit to my LBS, all to no avail, I removed the inner ring and inspected it carefully. I discovered that the teeth were not machined centrally within the thickness of the chainring material, resulting in a slightly wider shoulder on one side of the teeth. I reversed the ring and refitted it and the problem was solved. This was on a brand new bike, direct from the dealer.

[Cyclothesist]

...
Another poster reports problems with the middle ring on a tripe. If the chain 'rides' as described it only needs to do it once, under load, before it has carved itself a shoulder to sit on, and once it has done that, it usually gets worse and worse. However, there are only a few possible causes including:

1) no part of the correct big ring overhangs the spider arms, but the chain is somehow always thrown far enough by the correct ring for the chain always to mesh with the middle ring

2) the spider arms are slightly thicker than they should be.
3) the chain isn't really wide enough externally.(eg it is really a 9s ring/chainset and you are using 11s chain).

It may be possible to recover the situation in one of three ways:

1) make the spider arms slightly thinner.
2) file or reshape the tooth tops on the middle ring to a more favourable chamfer.
3) make some special spacers that sit between the spider arms and one or other of the chainrings, to function as a guide.

If contemplating the last of these, I would suggest that suitable spacers could be made using an old coke can, provided you can make half-reasonable 10mm holes in it. The procedure would first to cut strips about 14mm wide using ordinary scissors. Next, use something to make nice holes at least 10mm diameter near one end of each strip (tip; you may be able to 'cut/nibble' suitable holes using a good paper hole punch). Finally, you can fit the spacers in position, folding the plain end of each strip over so that there are additionally 1,2,3 or 4 layers above the middle ring/spider, but the chain is unlikely to get held up by the folded shim. In this way it ought to be possible to consistently direct even a narrow chain onto the middle ring.

Come to think of it, suitable guides could also be made easily, using epoxy resin/thread and given a metal facing if required.. The thread could be used to help 'bind' the epoxy resin in place provided the thread is applied whilst the glue is wet and there are suitable cutouts in the 50t ring.

Thanks Brucey. The problematic FSA Omega spider, rings and chain are all 9 speed. Filing the spider arms would seem to be the logical option, but probably difficult to do with great accuracy using hand tools. Additionaly it may mean I have a spider that's perfect for the FSA/Spa mixed manufacturer rings but nothing else.
A bit of on-line research revealed it's not that uncommon for chainrings from different manufacturers not to play nicely together due to differences in material thickness, bolt recesses, centrality/offset of the teeth etc. Another lesson learnt.
Another option is to buy a Spa Zicral big ring and fit that. It doesn't guarantee success, but with the Spa middle and granny rings happy on the FSA spider it's probably worth a try when I need a new big ring, or if the issue worsens beyond the current v occasional.

[Brucey]

...... Filing the spider arms would seem to be the logical option, but probably difficult to do with great accuracy using hand tools. Additionaly it may mean I have a spider that's perfect for the FSA/Spa mixed manufacturer rings but nothing else. .....

I think you can use a variant of the SG method it if you want. The trick here would be to mount the crank accurately in a chuck. I think you can make a suitable fixture using a crank extractor and some studding. The fixture would mount to the crank extractor threads. You can tell if the thing is running true or not before you start to dress anything. I think you can use a simple wooden fixture to help hold a dremel tool in the,right place, and the crank can be rotated slowly past it.

I don't think you need to worry overly about making the spider arms 'too thin' because it isn't difficult to add spacers if you have to..

[Mtb tourer]

I had the same problem on a 2014 XT chainset, new big ring and changing to the inner it fell between the rings. The profile was different, a standard chainring had a bigger gap between the rings. Find the code on the old chainring and buy the same one.

[Cyclothesist]

Thanks Brucey. A dremmel sounds like a v useful tool. I'll add one to my wish list.
Mtb tourer - you're right. And as we both found out - often you never know until you try. On the plus side I replaced the 30T FSA granny with a Spa 26T giving me a v useful gear for laden touring, so some good came out of the experience despite the big-middle minor incompatibility.

[Jdsk]

...
A dremmel sounds like a v useful tool. I'll add one to my wish list.
...

Mine's a genuine Dremel. It's cordless and I find that makes it much more convenient. Spare parts are available.

Similar tools are available in Aldi and Lidl special offers. I haven't tested either, but most of their tools are good.

Jonathan

[Brucey]

it should be possible to machin e the cranks in situ, using a fairly simple wooden fixture. BTW real dremel tools use a 1/8" tool shanks but a lot of similar-looking tools use 3mm ones instead. This apparently small difference can be significant.