| > the freewheel wobbled slightly.
> the owner said that this movement was normal.
> I got a resounding 'that's not normal'
I believe that some models of freewheel are designed to
wobble slightly for the same reason that some freewheel
cogs have twisted teeth... it makes the shifting more
positive. The cogs sort of wiggle their way into the
slots in the chain. If it weren't for techniques like
this there is a possibility that the chain could hit a point
where the side plates were riding on the top of the cog
teeth instead of the rollers riding between the teeth.
If the freewheel has no side play in it, it spins smoothly
and the cogs are tight, the wobble either normal or
harmless.
-John Wasser
|
| As John pointed out in .1 the freewheel wobble is almost certainly
normal. I've seen it (more or less) on hundreds of bikes, though it's
tough to see on some. The chain skip problem is almost always caused by
a mis-match between the chain and freewheel. Tight links, new freewheel
vs. old chain, new chain vs. old freewheel can all cause the mismatch,
as well as damaged teeth on the freewheel. Bad derailleur tension is
rare, but a possible cause, also.
Many folks recommend changing the chain and freewheel at the same time
to avoid the above, I'm somewhat luckier because I usually don't have
to.
ken
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| I bet its a bent rear axle. Take out the axle, take off all the
cones, washers, and nuts, and see how it rolls.
|
| The movement I had was definately more than slight.
As it turns out, he replaced the freewheel for me by the time I
dropped in to pick the bike up.
With the new one, I can detect no wobble.
I still find it interesting that they should wobble at all.
Thanks for the input.
Tom
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| Some wobble is perfectly normal. The question is where to draw the line.
Well, the tolerance of your derailleur, chain and free wheel system sets a
practical limit. For example, if the derailleur body must move x inches
laterally to effect a gear change, then an effective wobble of the cog on
the freewheel body of 0.1 x is no sweat, but 0.9 x could be a real problem.
A bent axle can cause poor wheel bearing operation, but unless the bearings
are loose, the wheel will rotate around the cones on the ends of the axle.
If there is a kink in the axle, but the cones still have decent clearance
to the races in the hub, then there is no wobble.
This reminds me of the time my advisor asked me to help tune up his
families bicycles. The rear wheel of one had a severe wobble. He started
to loosen the wheel, to shift the axle around to straighten out the wobble.
Instead I did a quick 5 minute wheel truing job!
But back to the free wheel. For a free wheel body to not wobble, the
tolerances of the threads on the hub with respect to the center of
rotation, and the corresponding tolerance between the races in the
freewheel body to the freewheel body threads, and cog teeth to cog mounting
to the body will all have to be very tight. Plus the bearings in the
freewheel would have to be very precise. This would all be a great waste
of money. The bearings in the freewheel are there for when you, the rider,
are goofing off. They rotate when you are not peddling, so are more a
convenience than a critical factor. When you peddle, the bearings don't
turn. True, they experience some compressive forces, but the ratchet pawls
in the freewheel take the drive force. So, bearings that are good enough
to not eat up much of the x tolerance discussed above, along with machining
tolerances for the threads the meet the same type of concern are all you
want to spend money on.
There will be considerable variation between freewheels, but this is not
likely to cause problems. The only freewheel wobble I ever had problems
with was when the bearing retaining ring came unscrewed, and I dropped most
of the tiny bearings along a fair stretch of Wisconsin highway! Now that
was a wobble! But it was the increasing noise that made me stop and check
it, not problems with shifting.
Del
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