woodruff key on flywheel - Yamaha ATV Forum
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post #1 of 11 Old 07-10-2009, 07:18 PM Thread Starter
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very pissed woodruff key on flywheel

waht would cause the woodruff key to keep breaking on the flywheel i have broken another one
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post #2 of 11 Old 07-10-2009, 07:44 PM
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well, what happens is after a key breaks once or twice the flywheel spins on the cranks and gets the hole out of round. To fix this a new flywheel is needed. But apply valve lapping compound on the crank and lightly seat the new flwheel, removing any burrs and nicks on the crank. Install a new oem key, tap the flyheel on lightly and torque the nut to specs. Dont forget to loctit the threads.

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post #3 of 11 Old 07-12-2009, 12:38 PM
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yeah and if your not torquing the nut tight enought that will cause it to break.... if you are torquing it to spec you might want to try going a little tighter.... be definitly do what motorhead said first
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post #4 of 11 Old 01-04-2010, 01:33 AM Thread Starter
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any other way of fixing the flywheel and crank besides buying a new flywheel
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post #5 of 11 Old 01-04-2010, 08:58 AM
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lap the flywheel with valve lapping compound and then use blue loctite.

The problem with trying to tighten/glue the flywheel is, if you have any weird issues that may stop the motor quickly you could wind up with a broken crank.

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post #6 of 11 Old 05-31-2010, 11:30 AM Thread Starter
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well i used the valve lapping compound and it helped getting the flywheel on but another problem has arose when i torque the bolt down and hit the starter the starter wants stay engaged if i loosen the bolt up it will disengage this warrior is getting to my last nerve if it aint one thing its another
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post #7 of 11 Old 05-31-2010, 10:31 PM
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Heres the real trick; fill the tank full of gas, pour five gallons of gas in a tub low enough to fit under your bike, back up 50-75 feet shoot with bottle rockets! Now go to the dealership and pick up a new yfz450x (or R). didnt have to purchace a flywheel or crank!
Sorry I couldnt help myself I had to do it Ive been having issues with atvs lately too. (not my yams though!)

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post #8 of 11 Old 06-01-2010, 12:29 AM Thread Starter
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hey no prob i have thought of alot of ways of catching it on fire but i do wanna fix it
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post #9 of 11 Old 05-31-2012, 08:32 PM
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great info

I have a 350 warrior i bought as parts that had this prob, sheared 3 keys before coming here (that wont happen again), the answers on this subject in this thread are dead on and worked awesome for me. I asked my machinist guy if he thought i could make my own from 1/4" square key stock (to keep from payin local dealership crazy prices) and he said yes it will work, and it may be the desired approach for someone who has really boogered things up because they could custom fit it to the damaged keyway and slot. Somehow my stuff wasnt damaged enough to go this route. With vernier scale in hand i measured what was left of the keys and found they are metric (duh lol), no metrics on hand here locally for me, so I decided to try a 3/16ths being it is almost identical in size (3/16ths is less than .009 smaller than 5mm, not enough to cause any timing issues and the morse taper is supposed to handle the majority of the work). I found napa/lowes/any hardware store w/ real selection has these on the shelf, its working at a fraction of the cost and no order n wait time. The cheapest i could find the "right" one for it was $4.08+s&h, rip off, i got mine for .58 cents, so I bought 3 n only needed 1 once i lapped the rotor to the crank. Definantly should tap the rotor into final place w/ a socket or pipe, dont wail it, just needs to be firmly seated. Done deal and riding the warrior again. Total cost including lapping compound and 2 extra keys was $7.06. If there is a next time on this machine i will get a 1/4" key and belt sand it to 5mm. I will post here again if the 3/16ths key has problems or if i shouldve used threadlock to enhance the tapers grip.
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post #10 of 11 Old 05-31-2012, 09:11 PM
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I kno this post is old, this prob w/ it not disengaging when torqued sounds like you are missing the washer behind the flywheel that keeps it from making positive contact w/ the lower timing chain sprocket.
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post #11 of 11 Old 03-27-2016, 09:19 AM
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I had the same problem with a used RT 180. Flywheel kept shearing the key.

I read these posts on Friday and realized I didn't understand the purpose of the key. I was only getting the nut snug enough to remove the play in the flywheel on the shaft.

I checked the parts diagram and noticed a spring washer was missing from the assembly so I got one from the local Yamaha dealer when I bought more woodruff keys.

I bought a torque wrench, set it to 50 ftlbs, installed the flywheel, washer, spring washer, and nut, then tightened using all my weight. Problem solved!

Even though the thread is old, it is still very useful - and applies to dirt bikes too.

Last edited by GooberSB; 03-27-2016 at 09:22 AM.
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