RD400 removing ignition rotor from crank shaft.

77RD 400. Can anyone out there provide a good walk thru for properly removing the ignition rotor from the crankshaft. I can't seem to find one anywhere on the net.

 

You need the official Yamaha puller (don't think there is an aftermarket alternative). It's basically a bolt with a long extension (about 8mm dia) that threads into the rotor once you have removed the bolt holding the rotor and points cam on. The extension fits into the hollow, tapered crank nose the rotor mounts to. Because the rotor uses a tapered fit, it usually doesn't come off just by tightening the puller. Sometimes it will come off with a 3/8" impact but I have also had to smack the bolt after it is tight with a hammer to shock the rotor off.

 

I did some cross-referencing to find this and believe it to be a correct tool. There are other brands but, if I'm correct with the dimensions, the outer piece threads into the flywheel and the inner bolt against the crank. Tightening these two pieces against each other pops the flywheel right off.
Do not smack the flywheel with a hammer in an attempt to "shock" it loose...you can weaken the magnet's "field".
https://bikemaster.com/motorcycle-tools-shop-supplies/flywheel-pullers/magneto-flywheel-puller.html
I ask that you do some due research to assess its suitability as I can not confirm its application.

 

That looks like a generic Japanese enduro flywheel puller, RD350/400 use a single bolt type puller. There are a couple bikemaster lists that might work with the right thread. However the end of the puller would butt onto the nose of the crank. Which is drilled out for the rotor bolt.

By the way, the rotor doesn't have magnets (unlike a typical Japanese mc alternator set), it is an excited field alternator, with windings in the rotor that are fed by brushes.

 

No magnets? Smack away!
Just kidding. I hate smackin' rotating assemblies.

I saw the single bolt "tool" but, not being familiar with this flywheel's mount, I couldn't see how it worked. Cross indexing tools based on the models that were listed as applications in other tools, and knowing that Yamaha had some rotor tools similar to this, plus the OP's difficulty in finding something, I thought I'd give it a shot.
The inner bolt on the tool I linked is not cone-shaped, it's blunt...it won't spread the end of the crank.
One of the single bolt "tools" I saw looked nothing more than a cheap, generic Chinese, roughly machined POS for, like, $2. I couldn't believe there wasn't a better solution. Me trying to find that better, dedicated bolt was like the OP's issue...couldn't find the definitive listing for the RD. When I did find it, it was a multi-application device like an old four-way lug wrench.
I checked Accu-Products/Accu-Mix 202 Racing figuring Rick Merhar might have something. Tho' nothing was listed, he might be worth a call.

 

Thanks guys, I'll pick up the Puller and let you know how it turns out.

 

FWIW I measured my old puller and the theaded portion is 10x1.25MM. The extension that fits into the drilled crank nose is 6mm (rotor bolt itself is 7x1.0mm weirdness) dia. by about 1.25 inches long. The extension is prone to bending/folding up if the rotor is really stuck on the taper. They can be a PITA to get off, especially if they've been stuck on, oh, 40 some years.