Chainring wobbles but is not warped

[hatofthecat]

I'm working my way through restoration of mid 70s Peugeot P10 and have a strange problem.

As I rotate the pedals the chainring is moving from side to side within the front derailleur as if the chainring is badly warped so that its almost impossible find a position in which the chain doesn't rub one side or the other of the front derailleur (no matter what gear is selected at the rear). As they were fairly worn I've replaced both the large and small rings with "new old stock" Stronglight ones, same as originals, but still the movement is there. Laying the old chainring down on dead flat glass desktop I couldn't see any warp to it.

Is it possible the arms of the spider are bent

Its a Stronglight TS Bis crankset I got off ebay to replace the Stronglight TS one that was on there as it had French pedal threads and left crank was some non-matching unbranded one. It was fitted to the bike by local bike shop mechanic as I didn't have the right puller for this crank type (have just ordered one from Spa cycles) and they also fitted a modern sealed cartridge bottom bracket, luckily English thread on this frame so easier option than trying to source original bb internals.

Reading around the subject I found some suggestions that taking the drive side crank arm off and trying in the different positions on the bb spindle may sort it, has anyone tried this with success ? Obviously once I have the puller in hand I can try this out myself. Could it just be down to some wear of the crank that is causing it to not fit squarely on the spindle ? I still have the original right crank so can try fitting that back on to see if it wobbles too (unfortunately as the "Bis" version looks different I'd have to find a matching left crank and someone to tap the pedal holes to 5/16 to make use of it otherwise I'm back on eBay hunting yet another English thread Stronglight TS crankset pair).

Pete

[531colin]

Yes, its worth trying the crank in different positions before using violence on the chainrings....https://www.google.co.uk/search?sourceid=ie7&q=chainring+straightening+tool&rls=com.microsoft:en-GB:IE-SearchBox&ie=UTF-8&oe=UTF-8&rlz=1I7SUNC_enGB402&gfe_rd=cr&ei=9rDpU9a0BISh8wfY74CgBg&gws_rd=ssl
Cottered cranks were worse, not that it helps you.....

[beardy]

I had this with a crankset.

After rotating it was clear that the problem was a misshapen taper hole, I still have the crankset in a drawer somewhere as it would have been wrong to sell it on with out a warning of its condition.

Beyond my abilities to reshape the hole.

The replacement crankset span perfectly true and that is the way to test if the problem is in the crankset or the axle.

[andrewjoseph]

Would some washers on the chainring arms help?

[hatofthecat]

I'll give the alternative positions a go then and if the crank's hole is just too far gone I will just have to take it on the chin and junk it Not keen on shimming the rings with washers as this is my "pretty" bike project

As I know the chainrings are totally straight I won't be inflicting any of those medieval torture tools on them

[OnYourRight]

Before doing anything else, make sure the bike shop tightened up the crank bolts to the proper torque (which is fairly high). Sometimes the crank wobbles until the bolt is completely tight.

[hatofthecat]

"tightened up the crank bolts to the proper torque" - yup on my list too. I think its a Shimano BB-UN55 bottom bracket that the shop mechanic put in. Can anyone point me at info for the correct torque for the crank bolt with the Stronglight TS crankset ?

Pete

[Indeboat]

It could possibly be that you have different tapers on the cranks to that on the BB.
JIC and ISO .
Sheldon Brown has a good article about them,
http://sheldonbrown.com/bbtaper.html

They both fit but not well,if they are both the same taper the crank goes almost all the way onto the BB,if wrong the crank will sit maybe half way on then as you secure the bolt it forces the crank on further but not all the way,this could cause a miss alinement.
Just a thought.

[mattsccm]

I had much the same thing. Tapers were worn.
Solved it with a hammer, tapping the spider to straighten things up. Obviously old chainset and I wasn't bothered about any theoretical stress to the spider. Just whack it.

[CREPELLO]

Good point Indeboat. It looks like that old Stronglight chainset may be ISO, wheras the Shimano BB is JIS. But the taper angle is still the same; it's just the ISO chainset will won't go all the way on the shorter JIS taper. So I don't think that's the source of the problem.

I wouldn't be surprised if the Shimano axle is defective. I know they have a good reputation, but I've had a defective UNxx BB once (mis-aligned threads).

I wonder whether it's worth applying just a smudge of grease on the side of the taper that the CS needs pushing further onto?

[hatofthecat]

"I wonder whether it's worth applying just a smudge of grease on the side of the taper that the CS needs pushing further onto?"

Yup, the old "take it off grease the heck out of the thing and bang it back on" ... definitely worth a try CREPELLO. Waiting on that crank puller from Spa before I can actually try some remedies out thus good to hear all suggestions now so can be ready to plan attack when it does arrive...

At least I have building up the wheels with vintage Mavic Module E rims and Normandy Luxe Competition hubs to keep me busy in meantime "a dishing I shall go"

[hatofthecat]

Okay I've now had the crankset off and tried it in the other three positions (heavily greased and fully torqued). Essentially 3 and 9 o'clock were worse and 6 o'clock was about the same so not worth moving the other crank round. Looks like I'm just going to have to try to find another crank Anyone got a Stronglight TS Bis right crank lying around in need of a home ?

BTW although the JA Stein crank puller from Spa Cycles works just fine I also found on eBay Germany another one (they do various other types too e.g. TA). Just go onto ebay.de and search for "crank puller stronglight". With postage about £30.

Pete