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my brother and i were taking the whole motor apart on my 99 kx 125 to rebuild it and SOMETHING, no idea what it is, fell out. :bonk::banghead:

That's a woodruff key. Look for a shaft with a slot in it.

JayC

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actually once the nut is torqued the snout taper holds the flywheel in place. the key makes it easy for dummies (including myself lol) to put the ignition parts back in the correct location. without that key, a dial indicator or degree wheel would be necesarry everytime you removed the flywheel.

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Flywheel would also spin out of alignment everytime you stall the engine violently. I've seen the flywheel key split in half when engine locked up :bonk:

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It could also be from primary gear could it? I i've never opened a kawi so don't know, but a 125cc pretty much only can have those in two places, flywheel or primary gear but primary gear might be different anyways.

Btw. the key can fall out unnoticed during assembly if you're not careful, maybe that's what happened?

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cant say ive ever seen a engine stall violently and turn the flywheel out of alignment but hey weird stuff happens everyday. people are still claiming aliens showed up at their house aswell. you could make the argument the key does hold the flywheel to some extent but IMO the taper does most of the work. if the taper had no functioal purpose, they would make the crank snout straight and have the flywheel just slide on and use the key as sole means of securing the flywheel from turning, but that aint the case. and i can tell you, that without that keyway slot in the flywheel, 99% of dirtbikers would be totally clueless where to put the flywheel back onto the crank.

and yes some bikes do use a key on the crank gear as well as the flywheel. ktm did that for many years. not sure if kawi ever did that. hondas that ive seen typically use splines on the crank gear side.

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cant say ive ever seen a engine stall violently and turn the flywheel out of alignment but hey weird stuff happens everyday. people are still claiming aliens showed up at their house aswell. you could make the argument the key does hold the flywheel to some extent but IMO the taper does most of the work. if the taper had no functioal purpose, they would make the crank snout straight and have the flywheel just slide on and use the key as sole means of securing the flywheel from turning, but that aint the case. and i can tell you, that without that keyway slot in the flywheel, 99% of dirtbikers would be totally clueless where to put the flywheel back onto the crank.

and yes some bikes do use a key on the crank gear as well as the flywheel. ktm did that for many years. not sure if kawi ever did that. hondas that ive seen typically use splines on the crank gear side.

rep +1

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If the taper would hold the flywheel by itself it wouldn't have a key, just a timing mark. I have seen a few flywheels shear the key off. Make sure you torque the flywheel nut to spec.

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Engines that backfire can sometimes shear a key. I've never heard of a smoker doing that tho'.

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Engines that backfire can sometimes shear a key. I've never heard of a smoker doing that tho'.
My '79 RM250 used to shear them with some regularity. :bonk:

I also have a great story about a sheared woodruff key. I Had a Hodaka Combat Wombat, and decided to enter a race with it. I was at the gate revving the engine when it inexplicably stalled. I kicked it half a dozen times and it fired back up, and seemed to run fine. When the 30 second board went up, like all the other riders on the line, I pulled in the clutch, put the bike in gear, and held the throttle open. When the flag dropped, I dumped the clutch, and the bike shot backwards out from under me, dumping me over the handlebars. I was stunned, and people were walking up to me to help, and whooping and hollering about what they had just seen, my bike had actually started and ran backwards. It turns out the key had sheared, allowing the flywheel to move and alter the timing enough that the engine kicked back and ran backwards when I re-started it.

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my friends 88 cr250 sheared one. miles and miles from the truck. still showed spark but wouldn't start. local mechanic was savvy enough to know it was common on that bike and suggested we look there. sho nouf $5 key and we were on our way the next day. had to leave it alone all night camouflaged in the bushes.

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My '79 RM250 used to shear them with some regularity. :bonk:

I also have a great story about a sheared woodruff key. I Had a Hodaka Combat Wombat, and decided to enter a race with it. I was at the gate revving the engine when it inexplicably stalled. I kicked it half a dozen times and it fired back up, and seemed to run fine. When the 30 second board went up, like all the other riders on the line, I pulled in the clutch, put the bike in gear, and held the throttle open. When the flag dropped, I dumped the clutch, and the bike shot backwards out from under me, dumping me over the handlebars. I was stunned, and people were walking up to me to help, and whooping and hollering about what they had just seen, my bike had actually started and ran backwards. It turns out the key had sheared, allowing the flywheel to move and alter the timing enough that the engine kicked back and ran backwards when I re-started it.

LOL...

That's a good story! I had a 1980 PE175 that used to run backwards if it was turned over backwards. What would do it was when stalling it on a steep hill then sliding down backwards and using the clutch and engine compression to slow the bike down - every now and then it would start up and run backwards... and it was in time and running good otherwise! Hey, the newer bikes don't do fun things like that!:smirk:

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cant say ive ever seen a engine stall violently and turn the flywheel out of alignment but hey weird stuff happens everyday.

I know they are totally different animals, but lawnmowers, pushmowers especially, will shear the key if you run over a root or rock or small child or something. They make the keys out of zinc alloy or something similar, specifically a soft metal so that it will shear when it's shock loaded. They do this to try to avoid bending the crank. I've seen it multiple times.

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I know they are totally different animals, but lawnmowers, pushmowers especially, will shear the key if you run over a root or rock or small child or something. They make the keys out of zinc alloy or something similar, specifically a soft metal so that it will shear when it's shock loaded. They do this to try to avoid bending the crank. I've seen it multiple times.

hahahahaha small child.. +1 for that :smirk:

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If the taper would hold the flywheel by itself it wouldn't have a key, just a timing mark.

actually the taper hold is pretty strong once the flywheel is torqued but im not going to argue this stuff any more. i can tell you, that if that key wasnt there, you and thousands of other dirtbikers wouldnt have the foggiest idea where to put the flywheel back on :bonk:. you have your theory why the key is there, i have mine :smirk:

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