tpchmara@wateng.UUCP (Tom Chmara) (05/05/84)
[this can get annoying...] I've just finished overhauling my bike; everything possible has been stripped apart and cleaned, and re-greased if applicable. Amid the hubbub, I decided to get rid of the old grungy chain and buy a sparkling new one. Problem: under load (i.e. hard acceleration) the chain skips on the rear cluster. I talked with a few bike shop techs, and I got stories ranging from "oh, your chain's probably got a stiff spot" (no, it doesn't) to "oh, didn't you know, you have to buy a new block (i.e. cluster) every time you change your chain (are they @$#@^ crazy? For a $12 chain I need a >$50 cluster? The present cluster shows VERY LITTLE wear). In case it should help, I've got a 1980-81 (around there) Norco Monterrey with Sun Tour 7-GT rear derailleur and a 13/24 6-gear cluster. The front derailleur is similarly Sun Tour. The chain is about 2 links long, but this only comes into play in low-low, so I've been lax about removing links. Sorry, I don't remember the make of the chain. Incidentally, either it's my imagination, but the problem seems to be SLOWLY disappearing; i.e. either I'm getting more careful about hard cranking or something is wearing into place. However, this is a slow process and may in fact be my imagination. Much thanks in advance, from both my bike and myself. ---tpc--- (Tom Chmara EE @ University of Waterloo)
tk@ecn-ee.UUCP (05/06/84)
#R:wateng:-97800:ecn-ee:18200002:000:1411
ecn-ee!tk May 6 11:57:00 1984
-
The bike shop "know-it-alls" are right this time: when there's a
discrepancy in the wear between the freewheel and the chain
(usually in the combination you described, i.e. new chain, old
cluster), the often inevitable result is skipping. You claim your
three year old freewheel shows very little wear -- do you know
what you're expecting to see? The wear shows up as a concavity on
the side of the freewheel tooth where the chain applies pressure.
You have probably noticed that the problem is worse on the
smaller sprockets.
On one hand, three years isn't a bad lifetime for a freewheel,
assuming that you use your bike regularly. (When I was racing, I
was lucky to get 8 months out of the block that I used for
training). On the other hand, what was the reason you replaced
the chain to begin with? (if there's nothing wrong, don't fix
it). My guess is that you use your bike often enough that both
freewheel and chain were ready to be retired. The alternative to
replacing the pair is to get a freewheel with readily available
replacement sprockets; this is practically essential with
expensive freewheels. However, I'd look for another shop before
spending $50 or more for a (decent) 6-speed freewheel; THAT
sounds like they're trying to sell you something you don't need.
--------
Tom Kirk
{allegra|decvax|harpo|teklabs|ucbvax}!pur-ee!tkhalbert@ucbvax.UUCP (Dan Halbert) (05/06/84)
Despite your cluster showing apparently little wear, the spaces between the teeth may be noticeably wider than they used to be. I have noticed this problem on well-used clusters only a few years old. Sometimes it seems as if the cluster and chain wear together, so it pays to change the chain fairly often (not just when it has gotten obviously stretched). I've noticed a different kind of skipping (or sometimes just clicking) when the derailleur and the cluster are not quite parallel. This is more noticeable on the "narrow" 6 or 7 sprocket clusters. For chains, most people I know choose Sedisport. It shifts nicely. --Dan, ucbvax!hlbert
chuqui@nsc.UUCP (05/07/84)
It is likely that the teeth on either your freewheel or your chainrings have
worn. As time goes on, chains stretch and the edges of the teeth get worn
round. When you put a fresh chain on, the tolerances are changed and it doesn't
fit the same so that it can start slipping. If you have softer metal in the
teeth than in the chain this can be exagerated. What you might want to do is
break the freewheel apart and replace individual cogs that show wear, which
is much cheaper than replacing the whole thing. Usually it is most noticable
on the smallest cog, but replace whatever cogs seem to give you the most
trouble.
chuq
--
From high above Benden weyr, Ch'qui, rider of the plaid dragon Plugh!
Chuq Von Rospach {amd70,fortune,hplabs,ihnp4}!nsc!chuqui (408) 733-2600 x242
ninety nine dead baboons, sitting in my living room...dsn@umcp-cs.UUCP (05/08/84)
Almost certainly you need a new set of rear sprockets. That's what it took
to stop my chain from skipping the last time I bought a new chain.
--
Dana S. Nau
CSNet: dsn@umcp-cs ARPA: dsn@maryland
UUCP: {seismo,allegra,brl-bmd}!umcp-cs!dsnsleat@aat.UUCP (05/09/84)
Among the alumni of the Naked Wrench Bicycle Co-Op, this is reffered to
as Garcia's Syndrome. I no longer remember who the original Garcia was,
but he had this problem. We use to see it all the time. It is indeed due
to the fact that the teeth on your rear cogs are worn, and yes indeed,
as your new chain wears out, the problem will go away.
Consider the situation: Neither the chain nor the cog teeth are very
flexible. If the pitch of the chain is just a slight bit different from
the spacing of the teeth, all of the load will be born by the cog and
link closest to the source of tension. As the link rolls off that tooth,
the load is suddenly transferred to the next link/tooth pair. This, by
itself, simply produces a rough "lumpy" transmission of power. If the
difference in pitch is great enough, as the chain shifts you get, in
effect, a wave propagating around the cog from the feed side, and it skips
a link. This is a little hard to describe without diagrams, so you'll
just have to work it out.
You shouldn't need to replace the freewheel every time you replace the
chain. The point is that unless the pitches are very closely matched,
they will wear at a much higher than normal rate until they are matched.
So, if you keep your chain well lubricated and clean, and replace it every
few thousand miles, your freewheels and chainrings should last a long
time. (Again, this implies starting with an unworn freewheel.)
If you have just one rear wheel or freewheel, then you could simply wait
for your chain to wear out a bit and forget the problem until next time.
If you want to be able to change wheels or replace the chain without
this problem, you pretty much have to replace that freewheel.
Incidentally, the two extreme chainwheel/freewheel combinations, small/small
and large/large are generally best avoided due to the angle the chain must
make. This is particularly true of 12, 15, or 18-speed setups.
Michael Sleator
Ann Arbor Terminals
{cbosgd, mb2c, psu-cs, uofm-cv, cosivax}!aat!sleatjoels@tektronix.UUCP (Joel Swank) (05/14/84)
The bike shop that said you should change the cluster with the chain is
correct. That's what they told me. I didn't believe it. I learned the hard
way. The chain slowly stretches as you ride. (if you don't believe it, hold
your old chain up beside your new chain.) As it does it slowly widens the
spaces in the rear cluster teeth. A new chain will have shorter links and
will not quite match the wider spaces in the cluster, therefore shipping
will occur.
If you do put a new chain on an old cluster and ride it far enough,
the two will slowly wear to match. The time I made the mistake, I was in
New Zealand and could not get a new cluster. It took about 1200 miles for
the skipping to go away completely. Now I change both the cluster and
chain every 3-4000 miles.
Joel Swank
Tektronix, Beaverton OR