worth replacing front chain ring and rear cogs on old Trek?



J

Joe

Guest
I bought a used Trek for $50 that I really like. I think it was made in
1996 since it's a Volkswagen Jetta Special Edition and from what I can
tell online Jetta gave away these bikes with the purchase of a car in
1996. Anyway, I like the bike, it feels comfortable but the chain keeps
falling off. I'm pretty sure the rear and front cogs are shot. Is this
worth fixing? Is it possible for a novice to replace these parts
myself? What else needs to be replaced along with it besides the chain?
What are some solid brands to look at? Should I just take this to a
bike shop and have them do it so it gets done right?
 
In the previous article, Joe <[email protected]> wrote:
> I bought a used Trek for $50 that I really like. I think it was made
> in 1996 since it's a Volkswagen Jetta Special Edition and from what
> I can tell online Jetta gave away these bikes with the purchase of a
> car in 1996. Anyway, I like the bike, it feels comfortable but the
> chain keeps falling off. I'm pretty sure the rear and front cogs are
> shot. Is this worth fixing? Is it possible for a novice to replace
> these parts myself? What else needs to be replaced along with it
> besides the chain? What are some solid brands to look at? Should I
> just take this to a bike shop and have them do it so it gets done
> right?


If you like the frame, keep it. It's that simple.

Since it's an old bike whose damage or loss pretty obviously wouldn't
break your heart, use it as a learning opportunity. Buy a mid-grade
chain, cassette and chainring and a few tools, and install them
yourself. Sheldon Brown can help:

http://www.sheldonbrown.com/k7.html
http://sheldonbrown.com/cribsheet-bcd.html

For simplicity's sake, it's probably best to get the same size
equipment (# of gears, teeth) you have now.

Then get out and ride.
--
_+_ From the catapult of |If anyone disagrees with any statement I make, I
_|70|___:)=}- J.D. Baldwin |am quite prepared not only to retract it, but also
\ / [email protected]|to deny under oath that I ever made it. -T. Lehrer
***~~~~-----------------------------------------------------------------------
 
Joe wrote:
> I bought a used Trek for $50 that I really like. I think it was made in
> 1996 since it's a Volkswagen Jetta Special Edition and from what I can
> tell online Jetta gave away these bikes with the purchase of a car in
> 1996. Anyway, I like the bike, it feels comfortable but the chain keeps
> falling off. I'm pretty sure the rear and front cogs are shot. Is this
> worth fixing? Is it possible for a novice to replace these parts
> myself? What else needs to be replaced along with it besides the chain?
> What are some solid brands to look at? Should I just take this to a
> bike shop and have them do it so it gets done right?


First things first. Before you start spending, measure the chain.

With the chain on the bike, grab a ruler and place one end in the
center of a rivet. Then, look at the rivet a foot away. Ideally, the
rivets would line up center-to-center.

It's likely, however, that your chain has elongated over time due to
wear (often called 'stretching', even though that's misleading).

The rule of thumb is that 1/16" of elongation is acceptable, but you
should replace the chain.

At the 1/8" point, you're probably looking at some new cogs and/or
chainrings as well.

If the chain is totally shot, you may be able to get away with
replacing only one or two chainrings. If most of your riding takes
place on the street, it's pretty unlikely that you'll need to replace
your granny gear. Rear cogs are not sold individually so you'll need to
buy a set.

As Mr. Baldwin pointed out, Sheldon is a great resource for DIY. You'll
need a few tools to do the work, but none of it is complicated or
expensive. At the least I'd get a chainbreaker, as I've had to fix
chains trailside as an emergency repair. At the most, you'll need an
allen wrench, chain whip, and cog wrench, all of which are good things
to have.

/s
 
Joe wrote:
> ...I like the bike, it feels comfortable but the chain keeps
> falling off. I'm pretty sure the rear and front cogs are shot.


The chain "falling off" is generally a symptom of a mis-adjusted
derailer, not worn parts.

When worn-out sprockets are an issue, the usual symptom is the chain
jumping forward on hard pedaling in some gears, and sometimes slow
shifting.

See: http://sheldonbrown.com/derailer-adjustment

> Is this worth fixing?


Almost certainly.

> Is it possible for a novice to replace these parts
> myself?


It is unlikely that any parts need to be replaced, on the basis of your
description of the problem.

Possibly relevant oilerplate:

Back in the old days, every tooth on a chainring was the same as every
other tooth on that ring.

Beginning in the 1980s, however, Shimano started experimenting with
different shaped teeth in different parts of the chainrings, with the
aim of improving shifting.

Newer chainrings typically have some teeth much shorter than others,
usually the teeth that are picking up the chain when the cranks are
vertical (this is when chain tension is lowest, and is the best time to
make the shift.

These special stubby teeth, often coupled with "shift assist" pins and
ramps on the side of the chainrings, make a great improvement in
shifting.

However, one drawback of this is that folks who aren't aware of this
design will sometimes discover the short teeth and will assume that
their chainrings are damaged or worn out! They aren't!

It is very rare to actually wear chainrings out, takes many, many
thousands of miles with a worn-out chain. When a chainring is worn
out, _all_ of the teeth show the wear, usually acquiring a hooked
appearance on the sides of the teeth that drive the chain.

For further information on this, see: http://sheldonbrown.com/chains

Don't be embarrassed about this...this is a _very_ common question, so
common that I have prepared this generic boilerplate response to save
re-typing.

Sheldon "Adjustment" Brown
+--------------------------------------------------------+
| There is no conclusive evidence of life after death. |
| But there is no evidence of any sort against it. |
| Soon enough you will know, so why fret about it? |
| --Robert A. Heinlein |
+--------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
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