Wobbling chainring

Hi All,
Sinnce I've installed a new BB my outer chain ring veres in and out about 5 mm. I just don't know exactly why because the cranks and BB seem absolutely fine. I did take the chain rings of and cleaned them a couple of weeks ago so perhaps I have not seated one of the bolts properly. Looks like I've got a lot of work to find out what it is.. Has anyone encountered anything similar? Of course now the FD intermittently rubs when there is a crossed chain line, and it's more of a problem than just trimming it with the front brifter. I'm running a mix of sora/tiagra on an old kuota Korsa
 
Hi All,
Sinnce I've installed a new BB my outer chain ring veres in and out about 5 mm. I just don't know exactly why because the cranks and BB seem absolutely fine. I did take the chain rings of and cleaned them a couple of weeks ago so perhaps I have not seated one of the bolts properly. Looks like I've got a lot of work to find out what it is.. Has anyone encountered anything similar? Of course now the FD intermittently rubs when there is a crossed chain line, and it's more of a problem than just trimming it with the front brifter. I'm running a mix of sora/tiagra on an old kuota Korsa

Hi and welcome to the forum, :)

If there is no noticeable play in the BB bearings (or axle), the wobble is probably caused by a bent chainring or improperly mounted chainring. Check if all the bolts are properly oriented and torqued. Use a criss-cross patter to gradually tighten them all to the specified torque.
(the picture is for handlebars, but the principle is the same for chainrings too)

Criss-cross bolt tightening pattern


Tightening bolts fully, one by one (instead of using a criss-cross pattern) can cause the chainring to not align properly and end up being a bit "warped."

Note - some cranks come with stamped chainrings (i.e. no bolts for mounting or replacing them).

Relja
 
Thanks for your prompt reply Relja.
So I went to investigate, loosened and retightened the the chin ring bolts as you advised no problems there. Then I noticed that there is some 'play' in the cranks and that they do waggle a little under stress but not without some pressure which is why I don't notice it unless I'm actually peedelling. The play is kind of 'spongy' the axle is able to move in the bottom bracket which is all wrong in my book. I have no idea why. I took the pedals off and attempted to tighten the bottom bracket using a specific 44mm bb spanner but I could hardly get it any tougher than it already is. I don't have a torque wrench and it would not fit this anyway if i did. I tried to remove the non drive crank arm which is not a self extracting bolt so I have to use a crank extractor tool. Problem now being is that the thread is getting stripped so I'm not getting any luck with removing it now. So I think I'm stuck which the problem. Probably a sub standard BB I got it cheap from China but I'm still not sure. The crank is a SRAM Gxp 9 speed K04. This is old kit now. Thank you for the advice, I have got the problem of getting the arm off now if I want to replace it or just living with it until I get something else.
 
Thanks for your prompt reply Relja.
So I went to investigate, loosened and retightened the the chin ring bolts as you advised no problems there. Then I noticed that there is some 'play' in the cranks and that they do waggle a little under stress but not without some pressure which is why I don't notice it unless I'm actually peedelling. The play is kind of 'spongy' the axle is able to move in the bottom bracket which is all wrong in my book. I have no idea why. I took the pedals off and attempted to tighten the bottom bracket using a specific 44mm bb spanner but I could hardly get it any tougher than it already is. I don't have a torque wrench and it would not fit this anyway if i did. I tried to remove the non drive crank arm which is not a self extracting bolt so I have to use a crank extractor tool. Problem now being is that the thread is getting stripped so I'm not getting any luck with removing it now. So I think I'm stuck which the problem. Probably a sub standard BB I got it cheap from China but I'm still not sure. The crank is a SRAM Gxp 9 speed K04. This is old kit now. Thank you for the advice, I have got the problem of getting the arm off now if I want to replace it or just living with it until I get something else.

This video might help (though a hammer with a rod could also be an option if the cranks won't be reused):


Relja
 
Thanks Sir
Sorry for the typos in my last post. They must be quite confusing for non English native speakers. I have to decipher what I was meant to write in the first place. It's pedalling and chain rings anyway. Good video link . As ever the problem is "I think I'm stuck". I suppose it is a case of "throwing good money after bad" (idiom) unless of course bicycle maintenance becomes an "end in itself"
 
Progress!
So I eventually, through more careful research, and actually measuring my cheap Chinese replacement bottom bracket that although it says that it is GXP compatible that is actually a lie. Of course because its so cheap, it would be uneconomic to send it back to China. That's how they get a lot of sales I guess. The info says that it is Shimano Hollowtech and SRAM GXP compatible which (so I have discovered) cannot be true. The reason for this is that SRAM GXP cranksets have a stepped spindle, 22mm on the non-drive side and 24mm on the drive side. The 24mm is the same as the Shimano Hollowtech 24mm spindles but Shimano is also 24mm on the non drive side. Shimano is a simpler and more straightforward design and the Chinese BB cups will accommodate this nicely. However because I decided to stick with a cheaper replacement SRAM Apex chainset, I was stuck with the SRAM GXP configuration. In the end I bought an original SRAM bottom bracket and followed the installation instructions. The cups screw into the frame nicely and are the same diameter and thread type as Shimano. However SRAM to avoid Shimano's copyright have adapted a wholly different means of attaching the non-drive crank to the spindle. All of this is explained in two separate videos which differ in opinion greatly. One is amusing, convincing and juvenile and the other is stoic and serious and MORE convincing. Both are absolutely fascinating! So I am getting a better tool to torque up my SRAM bottom bracket which is a thing of beauty. Now the reason why my crankset waggled in the Chinese BB is that there was 2mm of play at the non-drive end which also explains the 'spongey' play in the cranks. Its my fault of course for not researching this before I parted with my cash. But at least I have a spare BB cartridge if I go over to Shimano and the cheap BB may well work absolutely fine.
Anyhow I am grateful for your attention to this and I am really enjoying the Zen nature of the work. Putting the SRAM BB cartridge in today felt like heaven!
(Hambini)
(Joey Mesa)

Salutations!
 
Put it all together today, no waggle but still not happy with the freedom of the cranks to rotate if I spin it. The crank only spins a few times, but I took it on a test ride and it feels generally better so I will leave it at that, I think I've gained about 15 to 20 watts
 
Put it all together today, no waggle but still not happy with the freedom of the cranks to rotate if I spin it. The crank only spins a few times, but I took it on a test ride and it feels generally better so I will leave it at that, I think I've gained about 15 to 20 watts

That sounds good.

The crank bearings that spin too freely usually don't have enough preload (so effectivelly develop play when you put the load on them - because of the elastic deformation of the materials).
 
Thank you for your reply Sir.
I got in a bit of a rush between my day job and as soon as the crank arrived I was at it, rather than thinking and being very careful. I decided that I didn't need the Park tool bottom bracket tool as it was adding to my budget too much. @ £23 is a lot. But for some reason again. I can't remove my crank to adjust. What you say is reassuring but there are other videos which show more modern cranks spinning very freely. I am going to have to spend some time over the next couple of weeks being more methodical and thoughtful before I get frustrated and start damaging my new parts. ZEN! This is a philosophy and self control issue. My budget for the upgrade so far is about 150 euros.
 
Thank you for your reply Sir.
I got in a bit of a rush between my day job and as soon as the crank arrived I was at it, rather than thinking and being very careful. I decided that I didn't need the Park tool bottom bracket tool as it was adding to my budget too much. @ £23 is a lot. But for some reason again. I can't remove my crank to adjust. What you say is reassuring but there are other videos which show more modern cranks spinning very freely. I am going to have to spend some time over the next couple of weeks being more methodical and thoughtful before I get frustrated and start damaging my new parts. ZEN! This is a philosophy and self control issue. My budget for the upgrade so far is about 150 euros.

It is prefectly normal for things to not go smoothly or as planned.

Regarding the cranks' spin: they should not spin nearly as freely as the front wheel for example.
Play, or roughness (or binding) is bad, of course, but they should provide some drag.
On square taper cranks, the drag can easily be noticed when your ramove the cranks and spin the axle by hand. It should feel buttery smooth, but still provide some resistance.

Relja
 

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