Chain Hits both sides FD in 1 gear combination
09-09-16, 02:56 AM
#1
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Chain Hits both sides FD in 1 gear combination
Hey I had great help last time I had chain slip, hoping someone can help again 
My chain hits both sides of my front derailleur in the big chainring and middle freewheel cog, especially with force applied. It does get better after clean/lube but it still hits both sides.
Steel frame but ancient 1980s GT road bike. Cup and cone bottom bracket, the two cranks can be separated individually. I replaced the left crank with an aluminum one, the other is steel like most of the bike.
I've never tried the small chainring since that's 'shark toothed' anyways. 5 cog freewheel, only 3,4,5 I don't get chain slip on, I leave it on 3 all the time since the biggest ones make it too easy for a jackshow like myself
Actually I don't even have a cable on my rear derailleur since I never switch to another cog anyways.
So whats the deal?!
My chain hits both sides of my front derailleur in the big chainring and middle freewheel cog, especially with force applied. It does get better after clean/lube but it still hits both sides.
Steel frame but ancient 1980s GT road bike. Cup and cone bottom bracket, the two cranks can be separated individually. I replaced the left crank with an aluminum one, the other is steel like most of the bike.
I've never tried the small chainring since that's 'shark toothed' anyways. 5 cog freewheel, only 3,4,5 I don't get chain slip on, I leave it on 3 all the time since the biggest ones make it too easy for a jackshow like myself
Actually I don't even have a cable on my rear derailleur since I never switch to another cog anyways.
So whats the deal?!
09-09-16, 03:23 AM
#2
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Do you mean to say that, even with the FD centered over the chain's motion, the chain still hits both sides at different points in the pedal stroke? That would be pretty extreme... If that's the case:
1-Check to see that the front derailleur is straight.
2-Check to see that the chainring isn't bent.
It's possible that, if there are any such issues, they're being exacerbated by a noodly crankset.
By the way, is the shark-toothed small ring actually not working? If so, have you tried reversing it to see if that somehow makes it slightly more capable of functioning?
1-Check to see that the front derailleur is straight.
2-Check to see that the chainring isn't bent.
It's possible that, if there are any such issues, they're being exacerbated by a noodly crankset.
By the way, is the shark-toothed small ring actually not working? If so, have you tried reversing it to see if that somehow makes it slightly more capable of functioning?
09-09-16, 07:49 AM
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Also check the rear wheel is properly aligned in the dropouts / between the chainstays, and that your cassette (or, freewheel I assume) is not wobbly or loose.
09-10-16, 07:14 AM
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@HTupolev That's exactly what I mean, at the same position of each pedal stroke (around 3 oclock) is where it hits the worst.
Might be the chainring is bent, considering I was hammering away at it when taking it off (since the threads were stripped), doesn't seem like anything too bent just from looking at it.
The chainrings are welded on, its an old sugino crankset, so I don't think I can really take an individual chainring off.
I think the bottom bracket is loose, is this what you mean by 'noodly' crankset?
@Randybb The wheel is definitely straight in the dropouts, but I guess the dropouts could be misaligned? In which case I would need a frame alignment tool to really check properly?
Ya its a freewheel, its not loose or wobbly.
Might be the chainring is bent, considering I was hammering away at it when taking it off (since the threads were stripped), doesn't seem like anything too bent just from looking at it.
The chainrings are welded on, its an old sugino crankset, so I don't think I can really take an individual chainring off.
I think the bottom bracket is loose, is this what you mean by 'noodly' crankset?
@Randybb The wheel is definitely straight in the dropouts, but I guess the dropouts could be misaligned? In which case I would need a frame alignment tool to really check properly?
Ya its a freewheel, its not loose or wobbly.
09-10-16, 07:45 AM
#5
Mechanic/Tourist
Some thought and logic is needed here. If it's hitting on both sides on a particular chainwheel it can't be derailleur adjustment or a crooked wheel, or a freewheel problem. The only possibilities are (may be a combination):
Bent chainwheel.
Out of adjustment BB or loose cup(s)
Flexy frame/crankset (the former being more likely)
You first have to adjust the bb so that the cups are secure and there is no play in the bearings. Then make sure the chainwheel is running true with no side to side wobble. If the problem still exists then the problem is flexing under load, which is not avoidable.
Bent chainwheel.
Out of adjustment BB or loose cup(s)
Flexy frame/crankset (the former being more likely)
You first have to adjust the bb so that the cups are secure and there is no play in the bearings. Then make sure the chainwheel is running true with no side to side wobble. If the problem still exists then the problem is flexing under load, which is not avoidable.
