Yz426f 2001 woodruff key

I replace my woodruff key on my yz426f 2001 and it broke on me 2 blocks down the road how do you no if the woodruff key is on right ?and Also the flywheel

The tapered fit holds the flywheel on the crankshaft. The woodruff key is just there for alignment. If the key is breaking it's because the taper doesn't match the flywheel. The trick is to remove the key, apply lapping compound to the shaft and spin the flywheel back and forth a bunch until the entire surface of the shaft of flywheel has a buff appearance.

I unfortunately have to do a similar operation on tapered propeller shafts. Prussian blue shows high spots in propeller hub which then must be removed with a barrel grinder. Blue compound must transfer to 75% of inside of propeller hub, minimum. A similar test could be performed on your flywheel but on such a small scale it's easier just to lap it in.


Edited by 1987CR250R

Exactly as CR said, the key is only for alignment. The taper of the two parts, when the nut is torqued correctly, is what keeps them from moving and shearing the key.

Thanks will keep u posted

You lost me with the lapping compound ? Where can I get that loc auto shop ?

You may also see it sold as valve grinding compound. It is simply a paste with sand paper grit in it. It comes in many flavors, I would favor 180-220 grit to do a flywheel. 120 would work but is pushing the coarse end of the spectrum a bit far. Anything finer than 220 would take a lifetime to get any cut out of. I would also take a file and lightly cut the edge around the keyway as this often gets mushroomed outwards. So, roll the file around the shaft over the keyway. If there are any high spots they will become visible right away.

This is to much 4 me can't I just put sum valve compound in the key shaft hole and just put the woodruff key clean off the sides ?

That's what I got is it correct


That's the correct stuff. Is your crank key slot damaged in any way? As we've said, the key is simply for alignment purposes. It does not keep the flywheel from spinning on the shaft. The torque of the nut does that. That is, as long as the taper of the crankshaft and the taper of the flywheel are the same. The purpose of the valve lapping compound is to make the taper of each part match more perfectly.

My friend had to do this to his KLX450 after breaking a couple of keys and it's holding up. This might be helpful: http://www.pbase.com/mainecruising/fitting_a_prop

Edited by LucasLeader

Thanks guys didn't end up useing the valve compound I cleaned out the crank case taper and flywheel taper I installed a new key lol I ordered 5 woodruff so in case its holding up went out on a ride for a few hrs didn't really pass 45 50 mph but bike ran fine any real way off testing to see if its going to hold up ? Agian thank u

Large amounts of throttle followed by large deceleration, close to home! That will put a big load on it! Another thing you can do is to use Blue Loctite on the shaft taper. Loctite solidifies in the abscense of air and will add a little bit more holding power, and yet you will still be able to remove the flywheel without using heat if you use the Blue Loctite.

I think at least checking your fit with some prussian blue would have been a good idea. It's no fun when you pull your bike out of the truck for a weekend of riding and it breaks right after start up.

Hey gents, I am a new 4 stroke owner and I am having problems starting my 02 426F. It ran fine when I put it away for the summer, but now it won't fire. I have spark and fuel, but nothing but a couple close calls. Compression is a beast as it should be. I see a lot about the woodruff key, and won't be surprised if that is the problem. I just don't know where it is. On the right side behind the cover on the kicker shaft?? Any help to get me in the right direction would be awesome.

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