Should I replace my chain along with a new rear sprocket?

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NCKDX
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Should I replace my chain along with a new rear sprocket?

Post by NCKDX »

I recently bought a 2004 KDX220 and am rebuilding it. I am replacing the 52 tooth rear sprocket with a new 47 tooth sprocket to bring it back to stock 13/47 gearing, and am wondering if I am OK keeping the current chain. It is an o-ring style that measured 314.3 mm between 21 pins (the wear limit is 317.5 mm).

The further I get into this bike, the more how I see it was neglected. I haven't cleaned and waxed the current chain and am not sure how freely the links should rotate. The chain will bend under about 6" of its own weight, but it seems like it has a fair amount of resistance. I've never had an o-ring chain before thought.

Same question for the front sprocket. It looks worn but is not in bad shape.

Thanks,

Jason
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Re: Should I replace my chain along with a new rear sprocket

Post by KDXGarage »

It is best to replace all three at the same time. When one or two parts are worn some or a lot, it starts to wear the new(er) part(s) faster than normal. If you did not spend a fortune on the rear sprocket and decide to keep running the front sprocket and chain, then just let it go and eventually replace all three at once in the future.
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Re: Should I replace my chain along with a new rear sprocket

Post by bufftester »

+1 Usually best to replace together, although when I was running O-ring chains I found I could get away with chain replacement every other sprocket replacement. If the front sprocket is hooked at all best to do it now.
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Re: Should I replace my chain along with a new rear sprocket

Post by SS109 »

Jason wrote:It is best to replace all three at the same time. When one or two parts are worn some or a lot, it starts to wear the new(er) part(s) faster than normal. If you did not spend a fortune on the rear sprocket and decide to keep running the front sprocket and chain, then just let it go and eventually replace all three at once in the future.
I concur.

In addition, the chain will be too long. You'll need to take out some links. O=rings chains have a fair bit of stiffness to them due to the friction of the o-rings themselves. They don't don't need to be lubricated as they carry grease within the o-rings for the pins. You only use lube on them to keep them from rusting.
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Should I replace my chain along with a new rear sprocket?

Post by pumpguy »

I've found that O ring chains don't wear (stretch) nearly as much as non-O ring chains. Your pin distance dimension is well below the service limit. My manual says a standard 20 link (21 pins) length is between 317.5 - 318.2 mm. The service limit is 323 mm. If you're at 314.3 mm, that's better than new!

Try this. Lay your chain strung out on a flat surface with the pins horizontal, same as when its on the bike. Then using both hands spread apart 2 feet or so, grab hold of the chain with each hand and try pushing the links together and pulling them apart. Any movement between pushing and pulling? If no, then your chain is probably not worn. If yes, that's wear you're seeing.

When I got my KDX, it was really neglected and I had to replace just about every bearing; swing arm, linkage, steering head, and wheels. They were all bad, but that O ring chain was still nice and tight, even though both sprockets were worn and needed to be replaced.

Of course I will qualify that by saying I did not measure the chain's roller ODs, so there may be some wear there, IDK.

As with all things mechanical, YMMV, and use your best judgement to feel good about your work..
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Re: Should I replace my chain along with a new rear sprocket

Post by KDXGarage »

The older manuals stated to hang a 20 pound weight from the bottom run of chain, then measure the top run of chain.

I would suggest lubing ring chains, as the outside of the rings and the various pins and plates can benefit.
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