Chain jamming in front mech.

[Andy in Germany]

On a bike I'm repairing I've hit a problem. When changing up from the small ring at the front of the bike the chain catches under the screw on the mech as seen above, and stops dead.
The screw is tight, I've checked; it makes no difference.
Lowering the mech helps slightly; the chain stops once every three or four times I change gear instead of every time, but I've had to raise the mech because otherwise it comes into contact with the big ring.
Is there a solution apart from changing the mech?

 

[Ming the Merciless]

Can you put the screw in from other side, so the head is outside the cage? Then a bit of loctite to stop it coming loose.

My other comment is whether the derailleur is set too high? The bit of the cage that comes in beyond the screw is the bit that’s meant to derail the chain and push it onto the bigger rings.

 

[Andy in Germany]

Can you put the screw in from other side, so the head is outside the cage? Then a bit of loctite to stop it coming loose.

Unfortunately only the "rear" part of the mech in the picture has a screw thread, the "front" had a bigger hole. After the last 30 minutes I can also tell you it's a right royal gefummel to try and get the screw back in after I found this out. Do Not Try This At Home.

Eventually I found the "sweet spot by trial and error, which meant putting a bit of masking tape in the frame to mark the position of the mech, then move it 2-3mm; set up the gears try them, swear when it either jammed or rattled, and repeat. Now it works with just enough clearance from the big ring to the mech... about 1.5mm I reckon, but it'll do.

Now to sort out the original problem of the chain rattling in the middle ring. This was refusing to be resolved before but hopefully the properly positioned mech will help...

 

[Dogtrousers]

Adds gefummel to German vocabulary. You never know, it might come in useful.

 

[fossyant]

May need a longer cage mech.

 

[Ian H]

File the screw-head to a dome?

 

[classic33]

As above. Don't think it should be a cheese head screw

 

[Cycleops]

Looks like it’s the incorrect mech for that install and that protruding screw head doesn’t help. As @fossyant says it really needs a longer cage. Haven’t you got another FD you could swap?

 

[Big John]

Come on, Andy, if your place is like ours you're ankle deep in front mechs. If, after a couple of attempts, a part doesn't work properly we swap it out for another until we find one that does. We have drawers full of used components to the extent that we have an occasional 'cull' of the more undesirable, rust-ridden ones.

 

[presta]

Looks to me like you've got a front derailleur that's the wrong chainstay angle for the frame. If you put a 63-66 derailleur on a 66-69 frame, the chain will ride too low in the cage. Some derailleurs are available in only one version, others, like my Deore FD-M530, come in two versions, and you need to be careful you're ordering the right one:

When I bought my last front mech:

Me: "Hello, have you got an FD-M530-3 please"
Spa Cycles: "That's the Deore isn't it, yes we've got plenty of those"
"Yes, but have you got the -3 version for 63-66 chainstay angle"
"What do you mean?"
"They come in two different versions don't they, I'm looking for the one for 63-66 chainstay angle"
"Err...oh yes, so they do"

Selling bike components all day long, and never noticed that front derailleurs come in two different versions.

 

[Lookrider]

Looks to me like you've got a front derailleur that's the wrong chainstay angle for the frame. If you put a 63-66 derailleur on a 66-69 frame, the chain will ride too low in the cage. Some derailleurs are available in only one version, others, like my Deore FD-M530, come in two versions, and you need to be careful you're ordering the right one:
View attachment 689090

When I bought my last front mech:

Me: "Hello, have you got an FD-M530-3 please"
Spa Cycles: "That's the Deore isn't it, yes we've got plenty of those"
"Yes, but have you got the -3 version for 63-66 chainstay angle"
"What do you mean?"
"They come in two different versions don't they, I'm looking for the one for 63-66 chainstay angle"
"Err...oh yes, so they do"

Selling bike components all day long, and never noticed that front derailleurs come in two different versions.

Great reply from presta who got to the real ROOT cause of the issue ..filing or swapping anything round from how makers assembled something ( in any business) just advertises that what you are doing is somehow wrong...it may work but it's not the real solution ....and as presta pointed out even well known shops are at times "expectantly " unawares
Well done presta

 

[wafter]

File the screw-head to a dome?

... or maybe replace with a nice stainless button head..?

Looks to me like you've got a front derailleur that's the wrong chainstay angle for the frame. If you put a 63-66 derailleur on a 66-69 frame, the chain will ride too low in the cage. Some derailleurs are available in only one version, others, like my Deore FD-M530, come in two versions, and you need to be careful you're ordering the right one:
View attachment 689090

When I bought my last front mech:

Me: "Hello, have you got an FD-M530-3 please"
Spa Cycles: "That's the Deore isn't it, yes we've got plenty of those"
"Yes, but have you got the -3 version for 63-66 chainstay angle"
"What do you mean?"
"They come in two different versions don't they, I'm looking for the one for 63-66 chainstay angle"
"Err...oh yes, so they do"

Selling bike components all day long, and never noticed that front derailleurs come in two different versions.

Wow - tbh while that figures I never even considered that to be a thing.. top-shelf knowledge!

 

[presta]

Great reply from presta who got to the real ROOT cause of the issue ..filing or swapping anything round from how makers assembled something ( in any business) just advertises that what you are doing is somehow wrong...it may work but it's not the real solution ....and as presta pointed out even well known shops are at times "expectantly " unawares
Well done presta

Nobody notices because the wrong one will often work, so Madison didn't even bother importing both versions into the UK at one time. When I bought my first replacement mech in 2007 I had to buy it from Roseversand in Germany (who no longer trade with the UK since Brexit).

The original mech that Dawes fitted to my Horizon was the wrong one, because it was a bottom of the range C201, and that one doesn't come in two different versions. It worked, but it wasn't as smooth and slick as a correct one.

Every time I see people complaining of transmission difficulties I wonder why so few bother checking specifications and making sure stuff's compatible before they buy.

 

[Andy in Germany]

Every time I see people complaining of transmission difficulties I wonder why so few bother checking specifications and making sure stuff's compatible before they buy.

I think because it either doesn't occur to people there may be a difference, or when it becomes clear there is a difference the number of variables makes it seem a very daunting so people just try and make things work. I know I need to find out what is compatible with what, but I keep putting it off...