Chain not fully seated on big chainring

[Steve]

Got a question for those of you who are mechanically inclined.

For the past few months, I would get a serious amount of vibration in
the crank/pedals while in the highest gears, meaning the big chainring
and the two or three smallest cogs.

Finally invested in a workstand and I realized last night that the
chain, while on the big chainring, is not seated properly, meaning I
can see space between the chain and the teeth on the chainring.

I can push the chain down with my finger, of course, but the chain
won't stay all the way seated on the big chainring.

Doesn't seem to be a problem with the small chainring.

Anyone have any suggestions?

Bike's a 2007 Jamis Xenith Comp, 10-speed, compact FSA crank, Shimano
parts. Maybe 4,000 miles on the bike.

Thanks for any input.

 

[ZBicyclist]

Steve wrote:
> Got a question for those of you who are mechanically inclined.
>
> For the past few months, I would get a serious amount of vibration in
> the crank/pedals while in the highest gears, meaning the big chainring
> and the two or three smallest cogs.
>
> Finally invested in a workstand and I realized last night that the
> chain, while on the big chainring, is not seated properly, meaning I
> can see space between the chain and the teeth on the chainring.
>
> I can push the chain down with my finger, of course, but the chain
> won't stay all the way seated on the big chainring.
>
> Doesn't seem to be a problem with the small chainring.
>
> Anyone have any suggestions?
>
> Bike's a 2007 Jamis Xenith Comp, 10-speed, compact FSA crank, Shimano
> parts. Maybe 4,000 miles on the bike.
>
> Thanks for any input.

Original chain?
Is the chain "stretched"? From Jobst's FAQ's:
"The best way to determine whether a chain is worn is by measuring its
length. A new half inch pitch chain will have a pin at exactly every half
inch. As the pins and sleeves wear, this spacing increases, concentrating
more load on the last tooth of engagement as the chain rolls off the
sprocket, thus changing the tooth profile. When chain pitch grows over one
half percent, it is time for a new chain. At one percent, sprocket wear
progresses rapidly because this length change occurs only between pin and
sleeve so that it is concentrated on every second pitch; the pitch of the
inner link containing the rollers remaining constant. By holding a ruler
along the chain on the bicycle, align an inch mark with a pin and see how
far off the mark the pin is at twelve inches. An eighth of an inch (0.125)
is one percent, twice the sixteenth limit that is a prudent time for a new
chain."

If the chain is not replaced when it needs to be replaced, it will wear
the back gear cluster badly, and this means when you do replace the chain
you will have to replace the rear gear cluster as well. Because the large
front chainring makes less contact with the chain (if you are in 48-12 gear
the front chainring makes a new contact only 25% as often as the rear gear
cluster), the chain might be stretched but the front chainring has perhaps
not accommodated.

Best bet: measure chain, replace if needed. Be aware you might need to
replace the rear gear cluster as well.



--
Mike Kruger
Gravity -- It's not just a good idea. It's the law.

 

[[email protected]]

Steve who? writes:

> For the past few months, I would get a serious amount of vibration
> in the crank/pedals while in the highest gears, meaning the big
> chainring and the two or three smallest cogs.

> Finally invested in a workstand and I realized last night that the
> chain, while on the big chainring, is not seated properly, meaning I
> can see space between the chain and the teeth on the chainring.

> I can push the chain down with my finger, of course, but the chain
> won't stay all the way seated on the big chainring.

> Doesn't seem to be a problem with the small chainring.

What you describe is a difference in pitch between chain and sprocket.
To see the effect more clearly, hold a yardstick of metal tape measure
adjacent to the lower run of the chain on the bicycle and align an
inch mark with a chain pin. If the chain is in-pitch, all its pins
will lie exactly on 1/2" marks.

> Bike's a 2007 Jamis Xenith Comp, 10-speed, compact FSA crank,
> Shimano parts. Maybe 4,000 miles on the bike.

That's enough to warrant a new chain anyway, assuming you aren't just
riding on clean dry paved roads. A worn chain, often called stretched
even though nothing has stretched, causes rapid wear of sprockets,
driving and driven because only one tooth bears the load and engages
or disengages sliding under load.

http://www.sheldonbrown.com/brandt/chain-care.html

Jobst Brandt

 

[[email protected]]

Steve who? writes:

> For the past few months, I would get a serious amount of vibration
> in the crank/pedals while in the highest gears, meaning the big
> chainring and the two or three smallest cogs.

> Finally invested in a workstand and I realized last night that the
> chain, while on the big chainring, is not seated properly, meaning I
> can see space between the chain and the teeth on the chainring.

> I can push the chain down with my finger, of course, but the chain
> won't stay all the way seated on the big chainring.

> Doesn't seem to be a problem with the small chainring.

What you describe is a difference in pitch between chain and sprocket.
To see the effect more clearly, hold a yardstick or metal tape measure
adjacent to the lower run of the chain on the bicycle and align an
inch mark with a chain pin. If the chain is in-pitch, all its pins
will lie exactly on 1/2" marks.

> Bike's a 2007 Jamis Xenith Comp, 10-speed, compact FSA crank,
> Shimano parts. Maybe 4,000 miles on the bike.

That's enough to warrant a new chain anyway, assuming you aren't just
riding on clean dry paved roads. A worn chain, often called stretched
even though nothing has stretched, causes rapid wear of sprockets,
driving and driven because only one tooth bears the load and engages
or disengages sliding under load.

http://www.sheldonbrown.com/brandt/chain-care.html

Jobst Brandt

 

[Steve]

Thanks to both of you guys! Much appreciated.