Rear sprocket material

[Yzflier977]

So I bought my 2009 YZ450 about a year and a half ago and I'm on my 3rd sprocket.  In all fairness the first one that the bike came with wasn't in the best shape.  So in all actuality I'm on my 2nd one that I bought.  I've put 58 hours on the bike in that time and it seems that these 450's really go through the sprockets.  I ride exclusively MX and I clean my chain every ride and re-lube it both post wash and prior to riding.  I've been running a steel front and aluminum rear.  I've tried an inexpensive JT sprocket and the more expensive renthal sprocket.  I came from a 2 stroke and this is my first 4 stroke so I'm not sure if this sprocket wear is normal for these big 4 strokes or not?  I check my rear axle alignment with a set of digital calipers, not relying on the axle blocks so I know it's running true.  Finally to my question, has anyone run the dual compound sprockets like the twin ring or the supersprox stealth?  I'm wondering about the additional rotating mass affecting the bike handling in the air versus the longevity?  I'm not looking for input on recommendations for gearing, I'm happy with my 13/50.  I'm just looking for pro's and con's of running a dual compound rear sprocket, and what you've run with an idea of longevity?   Thanks in advance for the replies.

[WouldsAssassin]

Replace the final drive as a set. I think your chain is worn causing premature wear of the sprocket.

On my YZ I have over 50 hours on a very cheap Al rear sprocket. On my Aprilia RXV550 I have over 200 hours on a more expensive Al sprocket.

Either your chain is worn or you're throwing away good sprockets.

Edited October 16, 2013 by WouldsAssassin

[gscx]

Spend GOOD money on a chain. And the set will last

[Yzflier977]

First time I did replace them as a set with a DID chain, still wore prematually I thought. Learned my lesson on cheap chains already. Now I'm running a Pro-Taper chain because I broke the master link in the DID and ruined a couple links and it ended up being too short, hence new chain. I did put it on a used renthal rear aluminum sprocket but used in this case was the rear only had about 5-8 hours on it and I wasn't about to spend another $55 to replace a barely worn sprocket. I'm looking for input on the dual compound sprockets. And yes before someone else mentions it, I run my chain tightness to manufacturers specs, 50-60 MM at the bolt. Thanks.

Edited October 16, 2013 by Yzflier977

[grayracer513]

It's not the sprockets, it's the chain.
 
The most important consideration in making sprockets last is mounting a drive chain that lasts.  Sprocket wear is often attributed to things like sandy or muddy/gritty environments, soft materials, etc., and these do play a part in it, but the truth of it is that the single biggest reason that sprockets wear is because the chain wears to the point that it no longer fits the teeth.  
 
The roller chain on a YZ450 is a #520.  That, besides telling the width of the sprocket it should fit, also tells that the "pitch", which is the distance from the peak of one tooth to the next nearest is 5/8 of an inch, or .625".  The chain, then, has to be made so that the pins that the chain pivots on are exactly .625" from center to center.  This way, the drive load is distributed evenly among all of the teeth in contact with the chain.  As wear develops at the pins/rollers, and the chain is placed under tension, the "stackup" of this wear at each of 114 or so points adds up.  .001" at each pin makes the chain almost 1/8" longer overall.
 
As it wears in this way, it no longer fits the sprocket, and that means that instead of sharing the load among several teeth, it is carried only by the last tooth in contact at the top of the sprocket (or the first, if you look at the front sprocket).  The tooth stays in contact longer than it's intended to, which alters the angle at which force is applied to the tooth, and accelerates wear even more.  The top picture shows a normal, healthy chain and sprocket, the second one, a chain 2% longer than it should be.
 

Worn:
 

I run aluminum rear sprockets made by Tag Metals/AFAM.  They are hard anodized, and do last longer than the cheaper, raw aluminum sprockets like Sunstar and Renthal, but the main thing is the chain.  I use Regina ORN6 O-ring chains exclusively because the first one I ever bought lasted a year and a half in the desert on a CR500.  Each chain I've bought since that time has lasted between one to two years.  They currently cost about $90, so they aren't a premium priced chain. 
 
Sealed chains will last longer, but only if you avoid two common mistakes: never pressure wash the chain with the washer wand closer than 12" from the chain, or at any angle that allows water to be driven under the seals.  That washes lubricant out and dirt in.  Also, don't throw it in a tank and go after it with a wire brush.  Obvious reasons.  Use a chain lube that is not tacky once dried (so it won't collect stuff), and that will wash off easily with soap and low pressure water.
 
Yamaha states that the chain needs to be replaced once it reaches 2% over its original length in any one section.  You can measure from center to center of any number of pins, multiply the pin count by .625", and compare your measurement to that. A simple way to measure accurately is to use a typical 8-9" vernier caliper as shown below to measure 10 links:
 

 
Ten links measured inside to inside like that will measure 5.85" when new.  When it gets to 6.0", it's at 2%, and should be discarded.  I change them at 1.5%.

[Yzf_Buz]

Buy an Iron Man sprocket set from Nate at Dirt Tricks. They're the Best NO JOKE.