Flywheel

[slomo138]

The woodruff key is not used to hold the rotor on.It is only used to locate rotor to crank position for timing purposes.They use the torque of the nut on the rotor which has a tapperd hole in it to press it on a shaft which has a matching tapper on it for holding.

When I took my flywheel off to replace my woodruff key the fit between the flywheel and crank did not feel as tight as on other bikes I have owned.I pressed the rotor onto the crank by hand without the key in place and was able to spin the flywheel freely.All the other bikes I have worked on when doing the same thing have all had some type of friction.

To me it seems as if the taper might be off slightly.It seems a little tight on the out side or small dia. of the rotor hole.I will bring home some spotting dye friday and see how they match under different torque specs.If they are off slightly it can usually be fixed pretty easily by lapping the two surfaces together with valve grinding compound.

[slomo138]

This is a quote from the machinist hand book.

"Certain types of small tools and machine parts, such as twist drills, end mills, arbors, lathe centers, etc.,

are provided with taper shanks which fit into spindles or sockets of corresponding taper,

thus providing not only accurate alignment between the tool or other part and its supporting member,

but also more or less FRICTIONAL RESISTANCE for DRIVING

the tool.

There are several standards for "self-holding" tapers, but the American National, Morse, and the Brown & Sharpe

are the standards most widely used by American manufacturers.

The name self-holding has been applied to the smaller tapers¾like the Morse and the Brown & Sharpe¾because,

where the angle of the taper is only 2 or 3 degrees, the shank of a tool is so firmly seated in its socket that

there is considerable frictional resistance to any force tending to turn or rotate the tool relative to the socket."

On mine their is no frictional fit .It is as if the flywheel hits up against a stop.You should be able to feel

resistance between the flywheel and crank even with hand pressure before you put the fly wheel nut on.

[WR250fla]

You have posted exactly what I found out yesterday.

[David_Gronlund]

Excellent points. I am very curious to see how the spotting die goes. I've been kinda thinking the same thing about the tapers not matching up all that great, but then again no other year of this bike had a problem like this. Maybe they are using a different crank or flywheel manufacturer.

Please let us know what you find out in your research for the truth.

[David_Gronlund]

Another thing that I was wondering about is, for you guys that have had this problem. Did the crank get scuffed from the flywheel turning freely on the end of it with a sheared off key still protruding from it. I mean sheared metal can be very jagged, and if the flywheel still has a piece of the sheared key in it's groove, it may damage the crank a little. I wouldn't think that the world would come to an end with the damage, but you may have to use a FINE file to clean up the end of the crank a little. Maybe lap it in a little with some valve grinding compound.

Just wondering, because I don't know if a dealer would take that much time to check something like that when they fixed it for you.

[SPUTTER]

Yamaha needs to fix this. You are right about the taper.If you don't need a puller to remove the rotor - with a solid pop - its just not gonna work. The taper is critical - I would worry about using lapping compound to make the fix. If the rotor has an incorrect taper it should be replaced - phooey on different torque specs to fix it. Can you imagine that thing coming loose when you are alone and limping back from a crash way out back? Or just cresting that vertical lip on a mondo hill climb? Or just gassing it to clear that 14 foot deep chasm all your buddies just made? No thanks! ?

P.S. Just the fact that Yamaha has placed not less than three different successive torque values (for the rotor bolt) in the manual tells you they know there is a problem and they've been fishing for a cure. Bad business indeed.

If I had one of these bikes I would immediately check the rotor by pulling it to check the fit.

[RCannon]

One of my frozen beverage machines had a taper problem very similar to what you guys are talkingabout. The facotory fix was to use valve lapping compound to make the surfaces fit together properly..I wonder if that might help this situation???

[slomo138]

After checking fit of crank to fly wheel taper with spotting dye.It looked to me as if it was hitting slightly harder on the small dia. of the taper instead of even.So I tried fiting the two surfaces together with permatex valve grinding compoud.Each time I applied the compound I worked the flywheel back and forth for about a minute.After the third time I pressed the flywheel on by hand and could not remove it without a puller.New key,torqued to 47 backed off and retorqued to 47 ftp. Road all day today no problems.I don't know if this is the problem that caused the original to sheer but feel this will help stop it from happening again on my bike.

p.s.thanks Utvols,jetting workingout great so far ,just waitting for starter jet

[David_Gronlund]

Awesome slomo, thanks for the info.

I had read somewhere in TT that the flywheel puller is different on the 03 WR450 than the 426's. Is this true, do I need to order a new puller?

[jim-in-so-ore]

Yes, the Flywheel puller is something brand new.. It fits ONLY the 2003 WR250 & WR 450. thats the bad news... The other bad news is Yamaha only made enough for the dealers and has none to sell to the public (or said my local dealer). We had to borrow the dealers puller to remove the flywheel so that Steahly Off Road could design a weight.

Jim