I've needed to update this topic here for a long time, had a chance to do one with the sandcast I'm finishing, so here goes...
All of the motorcycle sprockets we get now and not machined parts, but are injection-molded and/or sandcast pieces. This causes a pebbly finish to appear in the teeth and on the sides of the sprocket, which wears off in about 50-80 miles and ends up jammed in the drive chain. This is the #1 source of short life in chains today, particularly on the 750. While the surface of the sprockets has become much better since I first wrote this here in 2006 and in my book (Page III-C5) about the finish issues on sprockets (particularly EMGO parts), but today this issue is far more widespread due to almost 100% of sprockets now being injection-molded parts from China.
So...to get best performance, power transfer, and most importantly LONG LIFE from your drive chain, listen up, here:
1. While much better than in 2006, the grit is still there: the JT Sprockets are better than most and are what I use nowadays. See pic.
2. The grit in the teeth is the enemy. The chain rollers will knock this off and jam it into the spaces between the sides of the link rollers and the sideplates of each link: this first locks up the roller, then grinds its way into the inner bearing surface of the roller. This wears the rollers and pins, quickly, making the chain uneven and longer, very soon. To stop this, remove the grit.
3. The first step in grit removal is to apply a wirewheel to the valley in each tooth. Use a softer wirewheel, not a hard one, for fastest and smoothest results.
4. The second step is to apply that wirewheel to the side of the teeth where the chain rides onto and off from the sprocket.
5. The third step is to see how you did, and possibly reapply the first 2 steps: polish the sides of the teeth withe fine emery paper. I use 1000-1500 grit for this, as it highlights any irregularities, especially grit.
6. The final step is to clean off all the grit you loosened. Then put the sprocket on the bike.
If you take the time to do this to modern sprockets you will get close to the legendary life we saw from chains like the Diamond XL/XDL on Honda's own sprockets: I've run 2 of those chains to more than 40,000 miles, each one, with less than 1 link-length of stretch, and only replaced the countershaft sprocket with the chains: the OEM rear sprocket went over 80K miles. That was done when Honda had their sprockets hog-cut in sprocket machines: those had NO grit on their teeth, and the base circle of the sprockets were +1mm over SAE spec, creating a -1mm tip-of-tooth length. Today I simulate some of that magic by trimming off 1mm from every tooth tip (grinder): while this does not increase the base circle, it does decrease the rollers' tripping over the tooth tips on their way into and out from the sprocket, quieting them a lot and saving that lost power. Since the torque is not being applied until 2 teeth later in the rotation, this does not stress any other areas of the chain nor sprocket teeth, so the wear on the sprocket itself is much reduced, as much as 20%+. While this isn't as much reduction as the larger base circle Honda's own sprockets offered (those were more than 40% reduction), it is still much better than off-the-shelf performance.
