Crankset problem - Stronglight triple

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ChrisF
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Joined: 22 Mar 2014, 7:34pm

Crankset problem - Stronglight triple

Postby ChrisF » 17 Jun 2019, 10:05pm

I've had this issue for a while now and I've tried various adjustments but it won't improve. It's 48/38/28 triple, and if I try to change from the 38 to 48 while the rear cog is one of the high gears (12 or 14) then the chain nearly always falls off the outer side. But if I change up while the rear cog is in a low gear everything works OK.
It's a down-tube changer with friction, not indexed. I've had the bike up on a stand and tried very carefully moving the lever while turning the pedals, and there's no position where it will change correctly - it either doesn't change at all or it's falling over the edge. If I adjust the front changer end-stop inwards it won't change at all (or fall off!). The changer cage looks in reasonable condition and is parallel to the chainrings.
Any ideas what might be wrong?
Chris F, Cornwall

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gaz
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Re: Crankset problem - Stronglight triple

Postby gaz » 17 Jun 2019, 10:15pm

I haven't any ideas myself but to help with diagnosis the model of chainset, chain and front mech may be of interest to others.

Post some pics if you can, particularly vertical and horizontal alignment of the front mech relative to the chainrings.

Is it a new problem? If so have you changed any parts of the transmission shortly before it occured?
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ElCani
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Joined: 5 Mar 2015, 11:24am

Re: Crankset problem - Stronglight triple

Postby ElCani » 17 Jun 2019, 10:23pm

If it’s possible for the chain to ‘easily’ fall off the outside of the large chainring then you need to adjust the limit screw. Put the bike in big-small (top gear) and adjust the limit screw to give the minimum gap that allows the chain to pass through the DR cage with no rubbing.

If you can’t shift into the big ring when the limit screw is set like this then (as you know!) you have another problem. Is the DR set too high? Position it so it clears the big ring teeth by just a couple of mm. you may need to reset the limit screw after doing this.

Is it definitely a triple front DR, with a cage profile that suits your chainring size?

Have you tried subtle adjustment to the angle of the DR cage? Some more modern DRs have shaped cages that can make it difficult to see whether they are parallel with the chainrings.

Cheers.

ChrisF
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Joined: 22 Mar 2014, 7:34pm

Re: Crankset problem - Stronglight triple

Postby ChrisF » 18 Jun 2019, 7:55am

Thanks for the replies.
I totally rebuilt the bike about 3-4 years ago, after a frame respray. The front derailleur is still the original (Shimano Deore LX) , chainrings new but same size as before. The problem wasn't happening after the rebuild but has got worse gradually.
The DR is less than 2mm from the teeth; I tried adjusting that. But thinking about it more, the fact that it all works OK when in a bigger cog at the back should lead to a solution - the only difference at the front will be that the cage is pushing just a fraction higher up and further forward than if the chain is on a smaller cog. I've now adjusted the cage (so it's not quite parallel now) and the action seems a bit better on the bike stand. I'll need to go for a test ride later to be sure and/or see if that's caused problems elsewhere.
Chris F, Cornwall

JohnW
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Location: Yorkshire

Re: Crankset problem - Stronglight triple

Postby JohnW » 18 Jun 2019, 2:41pm

I fitted a Stronglight 26-36-46 chainset about 3 years ago. The frame is a 1981 Pennine, which had been ridden with double and triple chainsets before being 'rested' about 10 years previously. I had the frame re-sprayed and checked over before I rebuilt the bike. The rear changer is a Shimano Ultegra long-cage. The freewheel block is a 13-28 six speed.

The front changer that I fitted was an Ultegra..................but I'd bought it some years ago, and it turned out to be the wrong variant of the model - the cage sides were profiled, but wrong profile for the chainset ratio, I had no-end of trouble, and eventually I brought out of my spares bucket a 20-years-old Campag long-cage front changer. The sides of the cage are not profiled. Even on the extremes (big chain-ring, small sprockets) it now changes perfectly.

I also use down-tube friction changers exclusively - and the chain goes where I tell it - not where a spring-and-hidden ratchet tell it. I had to get used to the replacement changer, as one does with friction changers, and the alignment of the front changer cage was critical, but all's well now.

In the light of my experience I think I'd check that the front changer was recommended by the manufacturer for the range that you are using on the chainset.

On the other hand - use of little sprocket on big chain ring isn't recommended by those who know best and you may be having to pull a bit hard on the lever to make the change you're referring to - the chain may be hesitant to move onto the big chainring at first, you may be unknowingly pulling too hard on the lever and then once the chain moves it moves too far. Maybe another pair of links on the chain may help that, but then you could be in danger of the chain being too long for use on small chainring/smallest sprockets.

mattheus
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Re: Crankset problem - Stronglight triple

Postby mattheus » 18 Jun 2019, 3:47pm

ChrisF wrote:Thanks for the replies.
I totally rebuilt the bike about 3-4 years ago, after a frame respray. The front derailleur is still the original (Shimano Deore LX) , chainrings new but same size as before. The problem wasn't happening after the rebuild but has got worse gradually.
The DR is less than 2mm from the teeth; I tried adjusting that. But thinking about it more, the fact that it all works OK when in a bigger cog at the back should lead to a solution - the only difference at the front will be that the cage is pushing just a fraction higher up and further forward than if the chain is on a smaller cog. I've now adjusted the cage (so it's not quite parallel now) and the action seems a bit better on the bike stand. I'll need to go for a test ride later to be sure and/or see if that's caused problems elsewhere.


Which way did you rotate it? I've fitted a couple of triples recently where I found tucking the tail in a bit made things better

(but to be honest I was rushing a bit, so it may not have been the best solution!)

mattsccm
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Re: Crankset problem - Stronglight triple

Postby mattsccm » 18 Jun 2019, 4:37pm

I had something similar albeit with a different set up. I put it down to the fact that whilst the chain should be in a fixed position at the front, it isn't when changing chain rings. If it's on the biggest at the back it's coming forward at more of an angle that if it was on a little sprocket and possibly less secure. Poorly put so think about angles and "stops/restraints" etc. Maybe this is the reason. Sounds like you have found the solution, don't change at the front when in the biggest sprocket.
Possibly this is a feature/limitation of less modern kit which often/when in good nick, does have more precise changing.
Can't think of any other ideas.

rmurphy195
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Re: Crankset problem - Stronglight triple

Postby rmurphy195 » 18 Jun 2019, 11:43pm

I have a similar problem - in my case using Claris brifters and front mech with the Spa triple., When changing up to the big ring when on either of the two highest rear cogs (=smallest) sometimes it needs an extra push on the lever to get things to happen properly, and occasionally the chain slips over the big ring entirely!

In my case I simply do the upshift when in one of the central cogs on the rear (8-speed) block, things work well then. Or do an upshift on the chainring and a downshift on the rear at the same time.

It is worth putting the bike on a stand and running through the gears, looking carefully at where the front mech make contact with the chain as you do the shifts, to understand what's really happening.
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Norman H
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Re: Crankset problem - Stronglight triple

Postby Norman H » 19 Jun 2019, 8:31am

The fact that it only happens when the chain is on the smallest sprockets indicates that its something to do with chainline. There may also be a clue in the fact that it all worked OK with new chainrings and presumably a new chain following the rebuild.

I've found that lateral wear in the chain can often have a detrimental effect on front changes. You can check for lateral wear by holding the chain on its side and seeing how much it deflects compared with a new chain.

reohn2
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Re: Crankset problem - Stronglight triple

Postby reohn2 » 19 Jun 2019, 8:48am

Are the any burrs or nicks on the inner cage plate that the chain is being caught on?
What BB axle length is being used,if it's too short that could cause it.
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slowster
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Re: Crankset problem - Stronglight triple

Postby slowster » 19 Jun 2019, 8:50am

ChrisF wrote:I totally rebuilt the bike about 3-4 years ago, after a frame respray. The front derailleur is still the original (Shimano Deore LX) , chainrings new but same size as before. The problem wasn't happening after the rebuild but has got worse gradually.

Did you replace the bottom bracket as part of the rebuild? If so, was it the same make and size?

peetee
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Re: Crankset problem - Stronglight triple

Postby peetee » 19 Jun 2019, 9:32am

I believe it's a chain line issue. The chain is probably in a state of extreme curvature when on the middle ring and smallest sprocket. Changing to the big ring is releasing it and it's willingness to straighten is throwing it too far. It's something I am asked to look for when bikes are bought into the workshop from time to time. Customers are sometimes a bit put out when I suggest to them that their 30 speed bike is, practically speaking, an 18 speed (on a good day).
It's not a fault of any one component but particular combinations of parts and frame geometry can make gear selection more fussy on some bikes than others and sometimes just fitting a new chain can cause it when it has never happened before.
Last edited by peetee on 19 Jun 2019, 9:36am, edited 1 time in total.
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Brucey
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Re: Crankset problem - Stronglight triple

Postby Brucey » 19 Jun 2019, 9:35am

given that the problem has become worse over time I think that is the way you should go about identifying/solving it too, I.e. working out what is different now vs then. Some possibilities;

- FD alignment
- FD adjustment
- FD wear/deformation
- chain type
- state of chain wear
- chainring type
- state of chainring wear
- BB length
- frame alignment

Its like magic really; easy enough to take for granted when its working OK but when front shifting isn't working it suddenly seems implausible that it should ever have worked in the first place.

cheers
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ChrisF
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Re: Crankset problem - Stronglight triple

Postby ChrisF » 23 Jun 2019, 10:56pm

Thank you all for replies and suggestions. Apologies for lack of reply; I have been away for a few days (with the problem bike!). Now that I have twisted the cage a little (tail inwards) it's manageable to change up if I'm careful. But I have also been viewing the ring closely as I pedal (on quiet roads!) and have discovered that the chainwheel 'spider' must be bent / crooked, the big ring moves sideways 1-2mm as it turns. It can't be the ring itself as I have swapped this out (I had a spare with similar wear). I guess this could be a BB problem rather than a bent arm on the spider but I won't know without detailed investigation which (while I'm on tour) won't happen just yet.
Chris F, Cornwall