Checking Stator & Fly Wheel

Discussion specific to the various air-cooled KDX models sold in the USA
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Boltonbubba
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Checking Stator & Fly Wheel

Post by Boltonbubba »

I have a recently rebuilt 1987 KDX200 and am checking the generator before i drop it back in the frame. The 3 wire stator ohm check i get is 55 ohms black to white-red and 0.8 ohms black to yellow. The fly wheel has a few small chips on the edge of a couple of magnets. When i put a drill on the fly wheel and spin it clock wise and measure the AC volts between black (also grounded on motor) and the white-red wire I get a little over 2.0 V AC. This bike is a 6 VAC system is that only off the lighting wire or should I be measuring something close to that on the wires that go up to the coil and CDI? Any help is greatly appreciated.
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Re: Checking Stator & Fly Wheel

Post by KDXGarage »

Welcome to kdxrider.net.
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Slick_Nick
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Re: Checking Stator & Fly Wheel

Post by Slick_Nick »

Don't bother with the drill spinny nonsense. Just measure the resistance of the stator windings and ensure that they fall within factory spec.
'00 KDX 220R
Boltonbubba
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Re: Checking Stator & Fly Wheel

Post by Boltonbubba »

So a few chips out of the magnets won’t matter much?
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Molly's 70
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Re: Checking Stator & Fly Wheel

Post by Molly's 70 »

How big are the chips out of the magnets?
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Re: Checking Stator & Fly Wheel

Post by bufftester »

Small chips on the edge of the magnets are not a big deal, as long as they aren't big missing chunks. More important is to ensure there are no cracks or gaps in the inside face of the magnet that the coil sits next to.

The Black to White/Red is your exciter coil resistance, and seems a bit low to me, but that's compared to the later series bikes (I don't have the service manual for the C models). The Black to Yellow is your lighting coil resistance, which also seems a touch low, but not too bad.

The 6V is a reference to the lighting circuit, not the output of the exciter coil. The output voltage will change based on the RPM of the flywheel, and if you're getting voltage it's likely fine. The real test is whether you get spark or not.

For the chips its always a good idea to use a bit of epoxy to seal the chip, just use it sparingly and make sure it doesn't get anywhere it shouldn't.
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Re: Checking Stator & Fly Wheel

Post by Boltonbubba »

Merry Xmas everyone and thx for your reply’s. I’ve tried to attach a photo of the flywheel. No cracks, just chips, largest is maybe the size of half of a dime. The Clymer stator test specs are looking for 54.5 ohms and 0.5 ohms compared to the number I shared above.
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9AEF6C03-3121-452C-B27D-7337625B6DB3.jpeg
9AEF6C03-3121-452C-B27D-7337625B6DB3.jpeg (3.58 MiB) Viewed 757 times
Boltonbubba
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Re: Checking Stator & Fly Wheel

Post by Boltonbubba »

Here is another picture where i circled w/ a pen the areas of imperfection
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Flywheel magnets
Flywheel magnets
80F3E510-7F34-461E-83CC-B70320DCFBD6.jpeg (3.22 MiB) Viewed 757 times
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Re: Checking Stator & Fly Wheel

Post by KDXGarage »

Did you re-do the epoxy or someone before you?

Did this bike run in your possession before the rebuild?
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Boltonbubba
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Re: Checking Stator & Fly Wheel

Post by Boltonbubba »

Someone must have done it before me, this came on a spare engine i picked up
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Re: Checking Stator & Fly Wheel

Post by Boltonbubba »

I’ve never had a bike running w/ this fly wheel
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Re: Checking Stator & Fly Wheel

Post by Slick_Nick »

It appears as though whomever epoxied those magnets back on, marked the flywheel with a grinder or something. I have to say though, that even if one of those magnets was off by a couple of degrees, your ignition timing could be altered quite a bit. Might cause you some issues.
'00 KDX 220R
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Re: Checking Stator & Fly Wheel

Post by KDXGarage »

OK, so this is not a "it was running, and now it is not" situation.

Do you have another one to look at or is that the only one?
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Boltonbubba
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Re: Checking Stator & Fly Wheel

Post by Boltonbubba »

I have two other flywheels that are in much worse condition. Are there any companies out there that recondition these?
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Re: Checking Stator & Fly Wheel

Post by Boltonbubba »

So put it all back together, connected coil and CDI…no spark. Changed the coil and CDI 2x to different ones I had…no spark. Tried it w/ the kill switch disconnected…no spark. I’m now thinking the fly wheel is the cause, don't really have any usable flywheels just another stator I could test. Any ideas on things to try?
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Re: Checking Stator & Fly Wheel

Post by Slick_Nick »

Try a new flywheel.
'00 KDX 220R
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Re: Checking Stator & Fly Wheel

Post by bufftester »

I can't remember where I read it, but I recall someone using an H series rotor and stator on an 87 or 88 KDX. IIRC they had to drill the stator plate holes for the proper timing, but I don't remember anything else. Might be worth a deep dive into the interweb pool.
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