There are some significant differences between the R2/4J and R5/6K. The main (non-cosmetic) differences are the ignition, the frame, and the swingarm. An R2/4J arm could be used on an R5/6K easy enough, but not vise versa, so it'm most likely an R2/4J.

Easiest way to tell is to look inside the frame, about 125mm up from the swingarm pivot. The R5/6K frame has a machined area there and a fitting for the torque arm (from the rear caliper) to attach to. As the R2/4J uses a similar setup to the MC16 and doesn't rely on a torque arm, it can easily be fitted to a later frame, but it's unlikely in most cases. The only reason I could see why someone would do it was if they found an '88 HRC swingarm and fitted it to an '89.

Not worth much, messing about with the motor how it is now. Just pull it apart. That's the only true way you'll find out how bad it all is, and whether it turns over or not isn't going to make any difference. In fact, if a crank bearing cage has broken up, which isn't uncommon on older cranks (and even some newer ones where poor oil has been used), then you could do more harm than good by trying to free it up!
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Andy.
NSR-WORLD.COM

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