My initial fitment of the Yamaha YM2C rear wheel in the Benelli swingarm showed me that some surgery was required. Specifically, I needed to employ the same technique I used on the The Bride’s Ninja 500 rear wheel back in 2001: cut off the part of the sprocket carrier that held the oil seal, and replace the carrier bearing with an “RS” sealed unit.
Unfortunately, this time around, the procedure proved to be a bit more difficult. No matter how I messed around with it, I could not get the casting chucked up in my lathe so that it was true and secure. (I could only get one or the other.) So, I resorted to lower tech methods. This modification doesn’t really require any precision except for appearance, so I held the sprocket carrier in the vice and went at it with the reciprocating saw.
Afterwards, I hit it with a sanding wheel in the angle grinder, then the detail sander, until it didn’t look obviously hacked up.
I still might need to figure out how to chuck this chunk in the lathe, if I need to shift the sprocket. However, I’m already looking at offsetting the engine slightly to the clutch side, so the further out I can run the chain, the better. We’ll see.
In the process of all this, I also discovered that I inadvertently overlooked one important detail: The JTR rear sprocket I ordered is for 530 chain, and the ATC250R countershaft sprocket is for 520 chain. Even though the YM2C and other Yamahas of that era used 525 chain, the only replacement spec’d for them now is 530, the same as early ’70s R5s and RD250/350s. There are conversion kits out there that would solve my problem, but they are very pricey, and would include an RD front sprocket I’ll never need. However, if there’s one thing I’ve learned in my years of chasing parts, it’s that manufacturers like to stick with existing configurations and any suitable substitute sprocket you might need has almost always been fitted to another model. It took a bit of sleuthing, but sure enough I found the same sprocket in 520, OE for ’83-’85 Yamaha YTM200 Tri-Moto ATVs.
Thankfully, I ordered the 530 sprocket through Amazon and I can send it back.
