Chain Skipping problem fixed by grinding sprocket teeth.

[Me]

Most of us know that a chain skipping problem is usually caused by
worn sprocket teeth (rounded teeth causing the chain rollers to roll
over them too early and skip). I was all set to head to the LBS (local
bike shop) and cough up $100.00 or more to get new chainrings,
cassette, and chain installed but remembered reading a couple of
websites that mentioned fixing the problem by filing or grinding the
pressure side of the sprocket teeth flat again. So I figured I'd give
it a try. If I screwed it up and it didn't work, I wouldn't lose
anything anyway because I was going to replace the parts anyway. I went
to the hardware store looking for a small grinding bit for my drill but
all they had was a 3/8th grinding bit which was a lot larger then what
I wanted but I got it anyway and as it turns out it fit perfectly in
the groove between the teeth. I didn't take long at all to buzz the
pressure side of the teeth on my 24 tooth granny gear flat again. I
jumped on my bike and went looking for a steep hill to check my work. I
was totally surprised there was no skipping at all. Has anyone else
done this? How many miles can I expect to get? I don't think bike
shops push this fix too much because they would much rather sell you
new parts. Here is a web site that touches on this subject.

http://www.utahmountainbiking.com/fix/index.htm
look under chainwheel

 

[Peter Cole]

Me wrote:
> Most of us know that a chain skipping problem is usually caused by
> worn sprocket teeth (rounded teeth causing the chain rollers to roll
> over them too early and skip). I was all set to head to the LBS (local
> bike shop) and cough up $100.00 or more to get new chainrings,
> cassette, and chain installed but remembered reading a couple of
> websites that mentioned fixing the problem by filing or grinding the
> pressure side of the sprocket teeth flat again. So I figured I'd give
> it a try. If I screwed it up and it didn't work, I wouldn't lose
> anything anyway because I was going to replace the parts anyway.

> I didn't take long at all to buzz the
> pressure side of the teeth on my 24 tooth granny gear flat again. I
> jumped on my bike and went looking for a steep hill to check my work. I
> was totally surprised there was no skipping at all. Has anyone else
> done this? How many miles can I expect to get?

Not very many. It's an OK fix to buy you the time you need to find a
good deal on replacement chainrings. Most chainrings are so expensive
you could throw the crank away...

 

[chalo colina]

Me wrote:
>
> remembered reading a couple of
> websites that mentioned fixing the problem by filing or grinding the
> pressure side of the sprocket teeth flat again. So I figured I'd give
> it a try.
....
> I didn't take long at all to buzz the
> pressure side of the teeth on my 24 tooth granny gear flat again. I
> jumped on my bike and went looking for a steep hill to check my work.
I
> was totally surprised there was no skipping at all. Has anyone else
> done this? How many miles can I expect to get?

This is a very difficult operation to do without changing the ring's
effective pitch. If you change the ring's pitch, you quickly wreck
both the ring and the chain, which in turn wears out your other rings.
This happens because a mismatch in pitch causes the chain's load to be
borne by a single tooth and roller at a time.

Of course, by the time you have reasons to contemplate such a crude
fix, most of the damage has probably been done already.

Your improvised repair seems like a good way to wring the last miles
out of a tired drivetrain, and with any luck it will serve you for a
useful amount of extra time. When the time comes that you have to
replace anything, though, do yourself a favor and replace everything
together-- the chain, cassette, and all three rings.

Chalo Colina

 

[chalo colina]

Benjamin Lewis wrote:
>
> chalo colina wrote:
> >
> > When the time comes that you have to
> > replace anything, though, do yourself a favor and replace
everything
> > together-- the chain, cassette, and all three rings.
>
> Why the rings, assuming they're not yet causing the chain to skip?

Because the old knackered chain will have worn them into an effective
pitch length that doesn't match the new chain. So the old rings will
quickly wear the new chain, which will then trash the new cassette.

Chalo

 

[Mike Jacoubowsky]

> Because the old knackered chain will have worn them into an effective
> pitch length that doesn't match the new chain. So the old rings will
> quickly wear the new chain, which will then trash the new cassette.

OK, dumb question time. You have a fixed number of teeth on the chainring,
and a fixed diameter. How can you change the pitch (distance between the
teeth) that the chain sees? Aside from nominal variations caused by
inconsistent grinding of the teeth?

If you're causing the chain to ride lower on the chainring, I can see where
that would cause a problem (because the distance between each tooth would,
in fact, be smaller at a point closer to the chainring's center).

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

 

[chalo colina]

Mike Jacoubowsky wrote:
> > Because the old knackered chain will have worn them into an
> > effective pitch length that doesn't match the new chain.
> > So the old rings will quickly wear the new chain, which
> > will then trash the new cassette.
>
> OK, dumb question time. You have a fixed number of teeth on
> the chainring, and a fixed diameter. How can you change the
> pitch (distance between the teeth) that the chain sees? Aside
> from nominal variations caused by inconsistent grinding of
> the teeth?
>
> If you're causing the chain to ride lower on the chainring,
> I can see where that would cause a problem (because the
> distance between each tooth would, in fact, be smaller at a
> point closer to the chainring's center).

Anything that causes the chain to sit closer in to the center of the
ring, as you point out, will cause a change in pitch. So any
subtractive process that touches the bottom of the gullet between
adjacent teeth is something to be concerned about.

But that's only one of the potential ways to change a ring's effective
pitch. Another is to change the loaded face of each tooth in such a
way that the roller climbs to a point _higher_ on the tooth than it did
originally. This is the usual effect of extreme chainring wear-- to
make the ring behave as though it had a slighly longer pitch than it
originally did.

Filing the teeth of a ring by hand can result in shorter effective
pitch, longer effective pitch, or variable pitch. But it is unlikely
to result in a ring that matches the pitch of a given chain.

Chalo Colina

 

[Me]

Thanks for your input, I was going to mention in my original post that
after I was done grinding the teeth I measured the distance between the
leading edge of one tooth to the next tooth to see that they all
measured 1/2" apart or close to it. To my surprise they were, probably
because I grinded back to almost to the trailing edge on every tooth. I
put together a crude web page to illustrate how I grinded the teeth.
Check it out Here --> http://hometown.aol.com/thepatriot1775/index.html

 

[[email protected]]

Mike Jacoubowsky writes:

>> Because the old knackered chain will have worn them into an
>> effective pitch length that doesn't match the new chain. So the
>> old rings will quickly wear the new chain, which will then trash
>> the new cassette.

> OK, dumb question time. You have a fixed number of teeth on the
> chainring, and a fixed diameter. How can you change the pitch
> (distance between the teeth) that the chain sees? Aside from
> nominal variations caused by inconsistent grinding of the teeth?

A worn chain has a larger pitch and therefore rides higher on the cogs
than a new chain would. In this process wear pockets, at the radius
on which the chain rides on exit, are formed. It is this larger pitch
into which the out-of-pitch chain rolls with every passage after
entering on the base circle. This generates ramps to the larger
radius (greater pitch) on which a new chain rolls up under load and
prevents engagement of incoming rollers.

> If you're causing the chain to ride lower on the chainring, I can
> see where that would cause a problem (because the distance between
> each tooth would, in fact, be smaller at a point closer to the
> chainring's center).

This is primarily a problem for driven sprockets, not driving
sprockets that are forcefully engaged under load. However, chain suck
on driving sprockets is another problem.

Meanwhile, because most sprockets are case hardened, modifying cogs to
accept a new chain is a short term fix because the sprocket is most
likely worn into the soft core if that is necessary.

[email protected]

 

[Sheldon Brown]

Jobst Wrote:

>>This is primarily a problem for driven sprockets, not driving
>>sprockets that are forcefully engaged under load. However, chain suck
>>on driving sprockets is another problem.
>>
>>Meanwhile, because most sprockets are case hardened, modifying cogs to
>>accept a new chain is a short term fix because the sprocket is most
>>likely worn into the soft core if that is necessary.

An obtuse anonymous poster pestered:

> Please explain how are aluminum sprockets case hardened.

"Most" sprockets are steel, which is case hardened by heat treatment.

It was obviously of steel sprockets that Jobst was speaking.

Sheldon "How Do You Case Harden Titanium?" Brown
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Phone 617-244-9772 FAX 617-244-1041
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[IK]

[email protected] wrote in news:MYzee.731$T3.4713
@typhoon.sonic.net:

>>> Meanwhile, because most sprockets are case hardened, modifying cogs
>>> to accept a new chain is a short term fix because the sprocket is
>>> most likely worn into the soft core if that is necessary.
>
>> Please explain how are aluminum sprockets case hardened.
>
> I guess since MTB's use 20t sprockets as chainwheels, the term
> chainwheel and sprocket have lost their distinction in bicycling. I
> failed to qualify sprockets to mean "gear cluster driven sprockets on
> the rear wheel." Does that answer your question?

Yes and no.
"Sprockets" in my book means the same as in yours - "gear cluster driven
sprockets on the rear wheel". No qualification was necessary.
The aluminum sprockets listed here though
http://weightweenies.starbike.com/listings/components.php?type=cassettes
can not be case hardened - unless you know of a way to case harden
aluminum.
You should have qualified "steel sprockets" when mentioning case hardening.
I am not sure that most sprockets nowadays are steel-made.

Later,
IK