Hi, new member here, just picked up an mc18.
It has the swingarm from a 2J / 4J but the fairings look like R5K, so I'm not sure I know which model it is... I suspect the 2j though. Can I tell from the frame number?

The bike has some serious issues, but finding these in Canada are rare, so I picked it up when I got the chance. I'm going to need some real help with this one.

The biggest issue is that the engine is seized. Do I need to get the engine moving before I try to remove the barrels? I've done a couple of top ends on other two-strokes but never a seized one. Any advice would be great.

Here she is :

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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Thanks Andy.
That's some good info on the R2/4J and the R5/6K. I'll look on the frame for a machined area for the torque arm tonight.

Appreciate the advice on the seized engine as well, trying to free it up could have been a coslty mistake!

I got her way below what I expected to pay, but like most bike projects, I'll be tossing money at it where I can.

Need to get it up and running is my first priority.