Posted by I am Tosk on April 30, 2010, 10:56 am
Can I just change out the rear sprocket on my daughters RMZ250, or do I
have to do both sprockets and the chain too?
Rowdy Mouse Racing, she is breaking off teeth now!
--
Pain is temporary, Glory is forever!
Posted by Tim H on April 30, 2010, 11:08 am
> Can I just change out the rear sprocket on my daughters RMZ250, or do I
> have to do both sprockets and the chain too?
> Rowdy Mouse Racing, she is breaking off teeth now!
> --
> Pain is temporary, Glory is forever!
If you're changing it because the sprocket is worn, then you need to
do the chain and countershaft sprocket too. If it's for a gearing
change and the chain and sprockets are in good shape, then probably
not.
If you put a worn chain on a new sprocket, the chain will load up one
tooth at a time until the sprocket is worn to match the chain stretch.
This happens because the new sprocket teeth are expecting the chain
rollers to be exactly 5/8" apart, so if the chain has stretched beyond
that then the chain can't spread the load across all of the links
wrapped around the sprocket; all of the load is picked up by the first
tooth the the chain contacts on the top of the sprocket. As you can
well imagine, this puts a huge load on that tooth and greatly
accelerates wear.
Tim H
Posted by I am Tosk on April 30, 2010, 11:12 am
In article <ea32f683-1cc4-4d46-8bba-388446f8c0e6
@a18g2000prd.googlegroups.com>, tntharrell@msn.com says...
>
> > Can I just change out the rear sprocket on my daughters RMZ250, or do I
> > have to do both sprockets and the chain too?
> >
> > Rowdy Mouse Racing, she is breaking off teeth now!
> >
> > --
> > Pain is temporary, Glory is forever!
>
> If you're changing it because the sprocket is worn, then you need to
> do the chain and countershaft sprocket too. If it's for a gearing
> change and the chain and sprockets are in good shape, then probably
> not.
> If you put a worn chain on a new sprocket, the chain will load up one
> tooth at a time until the sprocket is worn to match the chain stretch.
> This happens because the new sprocket teeth are expecting the chain
> rollers to be exactly 5/8" apart, so if the chain has stretched beyond
> that then the chain can't spread the load across all of the links
> wrapped around the sprocket; all of the load is picked up by the first
> tooth the the chain contacts on the top of the sprocket. As you can
> well imagine, this puts a huge load on that tooth and greatly
> accelerates wear.
>
> Tim H
Crap.. I just was pointed out yesterday that she is loosing teeth and we
are racing tomorrow.. Nobody has the parts I need locally so I don't
know what to do... What would you all do? Tighten it a bit and lube it
good, let her rip??
RMR, shit...
--
Pain is temporary, Glory is forever!
Posted by Rowdy on April 30, 2010, 11:29 am
Am 30.04.2010 17:12, schrieb I am Tosk:
> Crap.. I just was pointed out yesterday that she is loosing teeth and we
> are racing tomorrow.. Nobody has the parts I need locally so I don't
> know what to do... What would you all do? Tighten it a bit and lube it
> good, let her rip??
Loosing teeth is a very progressive act. The adjacent tooth will
see much higher forces from the stretched chain, making it fail much
sooner. The next one at the end of the gap gets an even more
"misaligned" chain roller slammed onto the flank, making it fail
even sooner than the other.
As the chain is reason for that misery a quick and dirty solution
is a _new_ chain. That might help stop the problem.
Changing the sprockets is harder as there are so many different types
of shaft fittings and rear hub hole distances. Tightening the
stretched chain will make the effect worse i'm guessing here. The more
you gas the bike the more force will be available to bend/break the
next tooth in line, so rolling and gliding through the race might help.
I remember one buddy riding his 250EXC with zero teeth at the counter
shaft, extremely loose (hence breaking) rollers and a very sad looking
rear sprocket. But he wasn't racing.
Rowdy
Posted by Volker Bartheld on April 30, 2010, 11:53 am
Hi!
On Fri, 30 Apr 2010 10:56:56 -0400, I am Tosk wrote:
> Can I just change out the rear sprocket on my daughters RMZ250, or do I
> have to do both sprockets and the chain too?
If the chainwheel is made out of aluminum, you might get away with two
chainwheels per chain/front sprocket because all the rest is steel and
wears out slower. However, if the chain itself is also lenghened (which
might be the case you're already losing teeth, the old chain might jump on
the new wheel.
Just check how far you can pull away the old chain from the new chainwheel.
If you're "seeing light", you might consider changing the entire set.
Next time, probably buy a steel chainwheel or one, where the inner "star"
is from aluminum and only the toothring is steel (like the Supersprox
Stealth). This setup lasts a lot longer.
Good luck!
Volker
P.S.: Check the chain gliders while you are at it. Sometimes they are worn
and chew on the swingarm or the rear cage.
--
@: I N F O at B A R T H E L D dot N E T
3W: www.bartheld.net
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> have to do both sprockets and the chain too?
> Rowdy Mouse Racing, she is breaking off teeth now!
> --
> Pain is temporary, Glory is forever!