Change gears with chain, or not?


6 replies to this topic
  • per_s

Posted June 03, 2005 - 02:55 AM

#1

Hi,
are you supposed to change front and rear gear/sprocket with the chain replacement?
My gears looks ok but I'm not perfectly qualified to judge that.
The chain broke and I don't know the history of my bike more than the latest 10 hours.
It is a 2000 YZ 426.
:)

  • walent215

Posted June 03, 2005 - 04:04 AM

#2

it is definitely advisable to change both sprockets and chain all together

  • RCannon

Posted June 03, 2005 - 04:14 AM

#3

If you change a chain early, sometimes you can get by with changing only the front sproket.

Obviously, new is better. If your chain broke, it probably points out a well worn parts. I would change everything to be safe. Rocky Mountain had sprokets on sale. They are not the best, but 19.99 for a aluminum rear sproket is tough to beat.

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  • phat_450f

Posted June 03, 2005 - 05:59 AM

#4

i would change f and r with the chain especially when there not that much. usually the chain and sprocket kits are great deals...

  • Ga426owner

Posted June 03, 2005 - 06:29 AM

#5

yes always change as a set ..........

  • grayracer513

Posted June 03, 2005 - 07:40 AM

#6

Under normal dirt bike conditions, a chain that was worn out will probably have worn the sprockets enough to warrant replacing them. A chain usually needs replacement because it's worn at the pins and bushings. This wear is small at each pin, but it adds up. Page 3-31 (or close to that) of your manual shows you how to measure a ten link section (you should measure several at random) to check for wear. The method shown subtracts the .400" size of the roller on the tenth pin. A new chain should measure about 5.85", and the wear limit is 6.00" (2.4% longer than new). A worn chain will also allow a considerable amount of lateral flex, and can be pulled up and away from the center point of the rear sprocket, even a new rear sprocket.

What this does is make the distance between rollers too long, and that lets the chain reach far enough from the last roller hooked on the sprocket to run against the chisel point of the next tooth as the chain rolls off of, or onto the sprocket under a load, instead of neatly down into the next valley of the sprocket. That wears the sprocket tooth off in the familiar "hooked over" or "ratchet" appearance the gear takes on.

So, if you're replacing a worn chain, your sprockets are most likely worn as well, and you should replace the set.

On the other hand, with the latest top quality O-ring chains being what they are, it's possible to wear a sprocket to the point of needing replacement without the chain needing to be replaced. The wear pattern will look different in this case. There will be no wear on the chisel shaped top of the tooth on either side when the chain is still the right pitch, only in the valleys of the sprocket. A "stretched" chain gives front sprocket teeth a "rolled back" look, and the rears, "rolled forward". Sprockets worn under a chain still at the correct pitch have the opposite appearance, with the front sprocket having a "hooked forward" appearance, and the rear sprocket teeth appearing thinned from the back side, but not hooked. The drawing at the top of 3-31 shows an exaggerated view of these two wear patterns. The one on the right is from a worn chain, the one on the left is a worn tooth as you would see if the chain were still good. The drawing would represent a front sprocket rotating clockwise, or a rear rotating the opposite way.

What that means is that if you have worn sprocket, you don't necessarily have a worn chain to go with it. Read the wear pattern, and check the chain for wear. It also means that you may not need to replace the whole set just to change your gearing. But if the chain is worn, even halfway to the limit, it will shorten the wear life of your new sprocket.

So, in short, when replacing the chain, usually replace the set. If replacing a sprocket, maybe not the set. In either case, inspecting the sprockets for wear will tell you more.

  • per_s

Posted July 04, 2005 - 02:39 AM

#7

Thanks a lot!
/Per





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