2006 YZ450 - SUPERMOTO - stator problem?. Help?

My son recently purchased this supermoto which was supposed to be all sorted out. He spent extra to get one that was "sorted" as he HATES electrical work. Long story short- he's been loosing lights almost every time he rides within 30 minutes.

Frustrated- he asked me to check it out (I'm an engineer but not great with bikes). System "looks" to be setup correctly although the battery is small (1.2Ah). I checked DC output at the rectifier/regulator and found only battery voltage- nothing more. So I checked AC input and found none going to the rectifier. Not sure if I'm testing it right? Does it need high revs to power an exciter? If run it with AC wires unhooked, will it hurt the stator?

I've been reading for hours on the stators and stator kits for this bike and I'm not liking what i'm reading but don't know if there is newer information (many posts on the moose/electrex kit date back to 2008). I spoke to the guy who sold him the bike and he says he installed a brand new aftermarket stator kit (with lighting output) just before he sold him the bike and he swears it was "charging" although the lights have never lasted longer than 30 minutes... ever. He doesn't remeber the brand but the bike still runs so at least the ignition side of the stator seems fine.

Any guidance on how to test this to see where the problem may lie? Any better stators available these days for the '06 and newer bikes? i don't even know if he got the oem stator but from my reading... i think he should have one if the failures haven't been addressed.



The YZ450 was never intended to have any spare electrical current to operate anything more than the ignition. The OEM stator is a tiny, 4 pole arrangement; two coils each fro each of two ignition circuits. When these are rewound in the aftermarket, the rewinder then effectively "steals" one of the two ignition circuits and rebuilds it to produce AC current for lighting. The remaining ignition circuit, using two of the poles, has to then be replaced by two smaller coils, each using only one instead of the original two poles, and being half their original size, they are forced to use smaller gauge wire to produce enough current to run the engine. That typically makes the ignition much less dependable, and most YZ450 lighting stators have one or the other circuits fail rather quickly. As far as I know, no one has yet managed to make one of them reliable

The lighting output that you eventually end up with is rarely any more than 55w AC at full power, which drops to around 35w when converted to DC. Hardly enough for anything more effective than a single DOT headlamp.

If you have no input to the rectifier, first remember that it's AC voltage at that point, so you have to use an AC VOM. If you're using the AC scale and you get nothing, check the stator for an open coil. As with the ignition side, the only way to get that much energy from so little copper is to use a very minimal wire gauge so there will be room for an adequate number of windings, and this makes them prone to fail from both electrical overloading and from vibration.

From a practical standpoint, there are only two ways to run lights on a YZ450. One is to run a straight, constant loss battery system with a battery having a fat Ah rating, or spend around $1500-2000 on engine hardware to convert it to use the stator from a WR450.

thanks for the response-

that does help and I have found the reason for no AC output. It seems the rectifier regulator is toast. Once I traced the AC wires back to the stator case, I unhooked them from the harness and found I had about 8 VAC between the 2 wires and the same between 1 leg and the bike frame. I believe the AC system is chassis grounded.

When I rev the engine, I get as much as 22-23 VAC so at this point, I "think" the stator is good. As soon as I plug the wires back into the rectifier though, I lose all AC voltage. I suspect an internal short somewhere so I'm going to try a new rectifier/regulator.

I've read about the wr stator flywheel upgrade but I have a couple of questions about that too.

1- I understand the crank (or at least half of it) needs to be replaced because of flywheel mounting. My company has a well equipped machine shop... I wonder if it would be possible to design an adapter to allow the wr flywheel to mount on the YZ crank? Are there any pictures of both showing the differences? Splitting the case is just too much.

2- I understand there are other parts needed - stator, stator cover, cdi etc... do these have to be from a certain year wr? IE. for a 2006 or newer YZ.. would the donor wr need to be 2006 or newer too?

Thanks in advance.

As far as I know, there are two problems to be overcome with hanging the WR flywheel on a YZ450 crank. The first of these is the diameter of the taper on the crank, which is, I believe, significantly smaller than the one in the WR flywheel. The second is the distance the rotor must sit outboard of the left main bearing to properly line up wit the WR stator. It seems to me that that there are two approaches one might take in making an adapter. One way is to make a go between piece, tapered on the inside to match the YZ, and outside to match the WR. There are some obvious problems with trying to secure the flywheel with an arrangement like this, and I doubt it's the method I'd choose.

Another way might be as simple as cannibalizing a YZ rotor, turning off the magnet ring from the center hub and rear (inboard) surface. Then cutting the center out of the WR flywheel, machining it to accept the center of the YZ flywheel, and welding the two together. I suppose it would even be possible to fab a new center for the WR rotor from scratch.

The left hand crankcase cover is needed to accommodate the WR stator, of course, and you have to do something about the extension on this cover for the WR e-start, either plug the motor hole and run it, or cut the extension off and build something to fill that hole. The cover may be magnesium as they are on the YZ. If so, it should be marked. Parts need to be from an '07-'11 WR450.


thanks so much for taking the time and excuse my picking your brain so much.

Last night, I installed a new rectifier/regulator but didn't have much success. I'm back to suspecting the stator.

As I mentioned, I only had AC voltage on 1 of the 2 yellow AC stator wires. When I hooked up the new regulator- the output was on 3.5 volts at idle. I had to rev the hell out of the engine to get 13v dc. Of course- when I hook up the battery, the regulator does not produce enough voltage OR current to ever charge the battery.

Can you confirm that I should be getting AC voltage out of both yellow stator leads?

No, because I have no idea who rewound the stator or how the wiring is laid out. I'm fairly sure that the yellows are two ends of the same AC circuit, though, so you should see ACV at both if that's true. I'm also not at all sure the AC circuit should show a chassis ground, but there again, I'm not familiar with that stator.

Contact one of our sponsors, Ricky Stator. They can give you more specific details on how to run this down.

thanks- i sent them an email.

Do you know of any posts or pics with pictures of the wr vs yz stator and flywheel?

No, not off the top of my head, but I can tell you that the YZ stator is 4 poles with two different coil circuits, while the WR is 12 poles wound as a single set. Very different. They'll produce about 80w just over idle, and can be rewound to put out around 140.

There are considerations involving adapting them to the YZ ignition, and it can be simpler to use a WR CDI with it.

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