woodruf keys breaking

[asasin]

Hi , My YZ 250 B motor keeps shearing the flywheel woodruf key . It has a DT fly wheel. Is this because the key is not a proper fit? The taper nut etc was tight and timing well retarded , this could have been a symptom of it shearing .,ie moving a bit.
 Any ideas . this is the third time it happened
 Cheers

[sleepy]

It's not the keys fault normaly. The key is only there to locate the flywheel, the taper should lock up and drive it.
Use some fine valve lapping paste between the crack and flywheel and rotate back and forth until you have complete contact. Then clean it all up re-assemble doing up the nut to the correct torque and it should work.

[William Doe]

Its because you keep using those budget CHINKA  keys that Joan sold you at 10000% mark up 

Seriously like Sleepy said ( Sleepy really thats the best you could come up with Sleepy  the whole universe of user names and sleepy , what about the other 6 dwarves  )

But i digress  the  ::)lack of imagination  of a user name aside hes spot on with his diagnosis and cure .

He obviously dosesnt know you as he suggest torquing it up ( not your usual tighten it till it strips and back it off half a turn 

I will be up next week to empty your fridge and soil your couch for the night , so we can look at it then 

Late edit (note to self , dont post while drinking and driving home somthings got to give  )

[asasin]

Thanks Sleepy Ill try that  , contrary to popular opinion I do own and know how to use a torque wrench .
 Statistically did you know that 6 out of 7 dwarfs are not happy

[80-85 husky]

one of them had relations with a penquin....

[asasin]

Thanks sleepy . I must have been asleep. key was holding flywheel form taper as you thought
 Cheers
John

[OverTheHill]

seen plenty that have sheard/shorn of over the years but luckily never had one myself but half of my crap dt's are running flywheels of something that been damaged before. Lapping them is the right way of course but being basically lazy i just do them up tight [like swing on a half inch breaker bar] but with a solid holding tool against the footrest or somewhere. In my pics up here somewhere is my RT1 with said holding tool.
I have a TT250 [ok you can laugh--was free though], & have advanced the ignition half a key width [left the key out] did it up with the same holding tool--swing on it method & had the daylights thrashed out of it with no problems. They're a big thread & never seen the end break off the crank through overtightening [always a first time lol]. The proper original yamaha nut is quite long so doubt if you'd pull the thread out of the nut either, plus original flat & spring washers are quite thick for added solid push--especially the flat washer. Anyway, my thoughts on a [not uncommon] problem.

[yamaico]

Statistically did you know that 6 out of 7 dwarfs are not happy

That reminds me of something that happened a few years ago. I was driving down to the shops one morning and rear ended a Mini. The driver jumped out and, bugger me dead, he was a dwarf. He came running up to me, all pissed off, and said "I'm not happy". "Oh yeah?" says I - "which one are you then?"

[JAP 454]

Yep, and early Triumph clutch centers were taper and key, bloody thing kept coming off on me T110, the late Max Evans of Caringbah Motorcycles showed me the way to fix it, " Grind it in like a valve seat, Virgil, without the key, clean it up, put a thin smear of paste on the taper, clean off the excess paste, leave a film of paste on there, fit the  key and give the clutch center a sharp tap on with a hammer and drift, fit nut and tighten, it won't come off again, Daaad, you'll have trouble getting it off again !!"
Foss

[pancho]

On tapers, the big problem is the key. (or the key to it is the key to it )  Make sure the flywwheel taper has no ridges ( from previous key ripping sh*t out of it.) Machine a mandrel to the same taper as the crankshaft. Lap the flywheel to the mandrel to get rid of high spots. Carefully file off any ridges or high spots off the crankshaft. MAKE a new key out of ALUMINIUM. Lap the flywheel to the crankshaft. Clean off the tapers to get rid of  lapping paste. Assemble the lot and hold the flywheel with a tool like 'over the hill' said and do it up bloody tight!
 The flywheel on my RT1 has a lot of grooves but no high spots, hasn't been a prob. for ages and I know that if it does slip on the taper the Aly key won't damage anything .
cheers.pancho.