Nightmare with changing between the front chainrings

[buzzy-beans]

Have you checked that the cable is routed correctly at the pinch bolt on the mech - if it is not it can cause problems?

But surely, as the entire mechanism appears to work correctly when not under load then the cable runs are presumably working properly?

 

[Racing roadkill]

You’re probably flexing the spindle, at the ring end, so that the ring is effectively moving too far away from the mech, when you’re making an effort. That’s possibly why it’s working at first, then not working. That would be my guess from what you’ve said.

 

[roadrash]

You’re probably flexing the spindle, at the ring end,...sounds like a job for @Fnaar

 

[Ajax Bay]

Earlier OP:

the mechanic said he had adjusted the limit screw, which had done the trick. However, before I even got home, it was not shifting again. Where there is normally a click when the gear is changed, there no longer was one and the cable and derailleur just fall back to the small ring. I took it back to the LBS and the mechanic inspected the shifter which he said was in good condition and working well, and fitted a new cable as the old one was worn, but again there is no click in the shifter and although the derailleur moves the chain over to the big ring, it falls back to the small ring as soon as pressure on the shifter is released. so the only front ring I can use is the small one/

it’s the sticky barrel on the trigger shifter issue.

+1 or sticky in the mechanism

I am [still] having a nightmare with the front mech / chainring on my 5 year old Sirrus Pro.
The main problem now is that the chain will not shift to the large front chainring . . . . the chain moves to the big ring the first couple of times I have tried it, but then stops doing so.
it might be time to give up on the bike, but it is only 5 years old and I would have thought it would have much more life left in it yet.
could have something to do with my weight, which at 15 stones, isn’t inconsiderable.
The front derailleur still moves over the outer ring, it's just that the chain doesn't move properly. There is a noise so you can tell the chain is rubbing against metal, which goes as soon as you shift back to the small ring position
I also tried giving the out limit screw a 1/4 anti-clockwise turn, but that didn't help. Eventually I snapped the cable so it's back to the LBS

where did the cable snap?

The OP has not answered this question.

I think the cable has snapped inside the shifter because when I move it at the shifter end, it also moves near the mech, I don't want to open the shifter at present because the spring tends to pop out and is a nightmare to get back properly.

He says "I snapped the cable" but doesn't say where but he "think(s) [it] has snapped inside the shifter". But he doesn't want to open the shifter because there's a spring in it.

I wouldn't give up on a bike just because of a shifting problem.

+1 If the OP sorts out this shifter and gets the limit screws and cable tension right riding the Sirrus should be a pleasure, in both chain rings.

wondering if it could be caused by a new rear wheel.

Nope

I wouldn't know if the gap at the bottom edge between the teeth is more or less than 2 mm. I would take photos of it in either position but as the cable is snapped at the moment, it won't operate at all/

Jam the FD as far as it can go to the right (unscrewing the H limit screw a turn or two (solving this requires more than 1/4 of a turn!). Measure the gap with a ruler. 2-3mm is good. Any more than 5mm is too high. The FD would need to be slid down (the seat tube / braze on) so that when the cage is positioned over the 50t chain ring (with the cage centred over the ring) the vertical gap is 2-3mm.
Pull on the cable from underneath the down tube. Does the cable come free? If not, it's not snapped (btw cables don't 'snap'; they may part or fail, unless gazillions Newtons of tension are applied.)

You’re probably flexing the spindle, at the ring end,

As far fetched as this may seem (unless merely @Fnaar bait) it is at least a suggestion ('cos the OP/we have not solved his problem) though it verges on the conspiracy end of the cock-up to conspiracy spectrum. NB The two lengths of the 'snapped' cable have not been sighted.) I can't see why a 15 stone rider (that's not 'heavy' in the scheme of things) would achieve this when there are thousands using the same FSA chainset entirely satisfactorily with so little 'flex' that the shifting is unaffected.
I'd unscrew the H limit screw a full turn at least, ride, pull the cable by hand and get the chain overshifting (throwing the chain even). This will demonstrate that this is not an FD issue (if correctly adjusted). From what the OP has said it may be that the detent in the shifter is failing to operate. Open the shifter (restraining the would-be errant spring) and (as well as seeing where the cable has 'snapped' (I have my doubts)) manual manipulation should determine if this is the issue and whether it can be put right (or if a new shifter (inexpensive) is required).

 

[iluvmybike]

But surely, as the entire mechanism appears to work correctly when not under load then the cable runs are presumably working properly?

takes nano secs to just check...

 

[Roadhump]

Earlier OP:


+1 or sticky in the mechanism


The OP has not answered this question.

He says "I snapped the cable" but doesn't say where but he "think(s) [it] has snapped inside the shifter". But he doesn't want to open the shifter because there's a spring in it.

+1 If the OP sorts out this shifter and gets the limit screws and cable tension right riding the Sirrus should be a pleasure, in both chain rings.

Nope

Jam the FD as far as it can go to the right (unscrewing the H limit screw a turn or two (solving this requires more than 1/4 of a turn!). Measure the gap with a ruler. 2-3mm is good. Any more than 5mm is too high. The FD would need to be slid down (the seat tube / braze on) so that when the cage is positioned over the 50t chain ring (with the cage centred over the ring) the vertical gap is 2-3mm.
Pull on the cable from underneath the down tube. Does the cable come free? If not, it's not snapped (btw cables don't 'snap'; they may part or fail, unless gazillions Newtons of tension are applied.)

As far fetched as this may seem (unless merely @Fnaar bait) it is at least a suggestion ('cos the OP/we have not solved his problem) though it verges on the conspiracy end of the cock-up to conspiracy spectrum. NB The two lengths of the 'snapped' cable have not been sighted.) I can't see why a 15 stone rider (that's not 'heavy' in the scheme of things) would achieve this when there are thousands using the same FSA chainset entirely satisfactorily with so little 'flex' that the shifting is unaffected.
I'd unscrew the H limit screw a full turn at least, ride, pull the cable by hand and get the chain overshifting (throwing the chain even). This will demonstrate that this is not an FD issue (if correctly adjusted). From what the OP has said it may be that the detent in the shifter is failing to operate. Open the shifter (restraining the would-be errant spring) and (as well as seeing where the cable has 'snapped' (I have my doubts)) manual manipulation should determine if this is the issue and whether it can be put right (or if a new shifter (inexpensive) is required).

Thanks for this which has obviously taken some time and thought. Fair enough, I hadn't checked the cable properly so after reading your post went and did so. You are correct, it hasn't snapped. The reason I thought it had was that it lost tension and went loose, but if I gripped it at the mech end, the other end near the shifter moved about. When I opened the shifter just now, the cable end is still fitted inside.

Unfortunately, when I opened it, the spring sprung, and I don't think I put it back correctly as the shifter doesn't seem to be clicking into either of its 2 positions now. I have to go to work soon, so can't do much more with it today anyway, so it's back to the LBS tomorrow.

I don't have the skills or expertise to fix this, but I do find it strange that 2 mechanics who are well respected in their trade and well reviewed locally, have looked at it (one several times), thought they had fixed it, but the fault re-occurs every time. Perhaps a complete strip down and reassembly might help, but if that proves expensive I might be more inclined to cut my losses and go for a new bike.

Thanks again.

 

[confusedcyclist]

Be sure to test ride it again before you take it away from the mechanic! If you don't know what you are doing, you could be stacking one problem on top of another making your life more difficult when you troubleshoot it. It certainly sounds like you didn't put the shifter back together correctly, maybe you had a simple limit screw problem to start with, but then tinkering around with other parts, you made it worse!

 

[Nigelnightmare]

You should always ease off when changing gear (front or rear) up or down, this will make the changes smoother and everything will last longer.
I had a similar problem with my recumbent trike.
I had set it up according to the FD manufacturer's instructions, it worked on the stand but not when ridden, so I loosened the outer stop to increase the throw on the FD and that seemed to cure it.
Don't go mad or the chain is likely to come off the outer ring.

HTH

 

[Deleted member 35268]

Can we get some pics of the setup please. Pic of shifter, derailleur and your double crankset. If possible.

 

[Roadhump]

Thanks for the help and advice, all. This problem has been happening for several months now, despite the efforts of a couple of good mechanics. The bike has become like the old problematic Triumph Spitfire of Stag - a lovely thing when it works, but consistently unreliable.........well that's my justification anyway, for making it an n+1 moment. I am replacing it with a new Btwin Triban 540 flat bar, I need a reliable bike for the work I do as a cycle instructor, and prefer a flat bar for that purpose. So I am giving up on the Sirrus and starting afresh.

I am keeping hold of the Sirrus for now and may use it to learn a bit more about cycle mechanics - I can't see it recouping much of the outlay on my new bike if I sold it, and when my finances are somewhat replenished, I may come back to it and re[place the whole drivetrain.

Thanks again for the help and advice.

 

[mikeymustard]

Thanks for the help and advice, all. This problem has been happening for several months now, despite the efforts of a couple of good mechanics. The bike has become like the old problematic Triumph Spitfire of Stag - a lovely thing when it works, but consistently unreliable.........well that's my justification anyway, for making it an n+1 moment. I am replacing it with a new Btwin Triban 540 flat bar, I need a reliable bike for the work I do as a cycle instructor, and prefer a flat bar for that purpose. So I am giving up on the Sirrus and starting afresh.

I am keeping hold of the Sirrus for now and may use it to learn a bit more about cycle mechanics - I can't see it recouping much of the outlay on my new bike if I sold it, and when my finances are somewhat replenished, I may come back to it and re[place the whole drivetrain.

Thanks again for the help and advice.

I think it's very useful for everyone to know some mechanic-ing, but I'm sure it would be particularly useful for a cycle instructor!