It was time to replace sprockets and chain on our 2009 RMZ-250, and I ordered in a Sunstar 32212 front sprocket. It wouldn't fit. It was too thick by a tiny amount, about 0.2mm. Just enough the circlip groove wasn't exposed enough for the circlip to drop in.

At first I thought it was play in the countershaft, and tried to make sure the shaft was "out" when pushing the sprocket "in", but there wasn't any play to speak of. Next I made sure the spacer behind the sprocket was seated tightly as the dual o-rings can make it move out a bit. Still no go.

Not having time to wait for a Suzuki sprocket to be brought in from the dealer, I decided to make a light cut on the raised portion of the sprocket with my lathe. No go. Way too hard with the heat treatment used.

So I did a rather "unrecommended" procedure and held a grinding bit against the sprocket raised portion at 90deg. I spun the sprocket at high speed on the lathe and the grinding bit was spinning at high speed in my Dremel tool as well. Sparks flew, but it did the job. Surface texture was a bit grainy, but miraculously flat and true. Probably will rust really fast with the blueing/anodizing, or whatever it is, gone.

So, I'm not sure if the problem would be there on all RMZ-250 engines, or with all 32212 sprockets, but next time I'll go with the OEM part.