WR450F Problem - Work Around

I found a bike with 26 miles on it for $4500. Can't beat the price. Looks like a few things with this bike cause all of the failures:

1) The Jetting on the carb is too lean and causes backfires

2) The rotor nut is not properly torque at the factory

3) The taper on the rotor is too short and too steep, so a higher torque, lapping and loctite are need to make it stay in place

4) The starter gears do not roll backwards

5) So, when the rotor turns backwards due to backfires, the rotor spins but not the flywheel breaking the woodruff key, killing the timing, thus no starting

6) Simple answer, lap rotor, torque, and loctite rotor nut, properly jet to prevent backfires (Oh Yeah, it will run like a beast with proper jetting)

7) TAKE THE GEARS OUT OF THE STARTER, the real problem is the starter gears DO NOT roll backwards

Well, I took to the local shop that sold the bike to the original owner in April this year. They are rechecking the rotor torque and woodruff key. I will have them take out the starter gears before I bring it home. E-start is cool; not pushing a bike 2 miles is cooler.

Boy are we all stupid!

You figured all this out in 10 seconds.

Thanks for sharing!

Nope, just a newbie. After a week of reading all 5000+ posts around the web this is what I found and put it all in one post. No one had the answer in just one post. Just trying to help out the next newbie.


Just trying to help out the next newbie.

And your post most certainly will. There is alot of discussion about lapping and locktite, but the real problem is the design. Whimpy little starter with no stamina and gears that do not disengage. If I rode a 450 my first mod would be taking the gear out of the starter. I don't mind kicking, but pushing sucks. Good summary. :)

The problem is in the taper of the crank is either poorly machined or designed. I tend to think its probably both. None of the people that I know have had a problem have had a problem with their WR450s so I wonder if it was a run of bad flywheels or crankshafts.

Lapping 2 hardened surfaces will remove nothing. Using glue is a yard ape fix.

Yamaha screwed up and dosn't want to admit it or pay the costs to make it right.

I always take my cellphone with me.

if you'r not using the e-start you'll be able to remove the battery and starter to save weight! with the battery out you can also remove or alter the top of the air box to let it breath. have fun.

So the crank - fly wheel problem is caused by the bike backfiring and the starter gear doesn't spin freely in reverse.?

My mechanic said You can't remove the battery. I t will ruin the stator according to him.. ANYone know about what's involved with taking off the starter and removing barrery.. If you're not going to have e-start might as well lose 10 pounds..

Dave, Yes that's what it seems to be.. They always spin when e-starting as far as I know and a backfire is usually part of the deal. Jim

i've read posts that have said there is no problem pulling the battery but the juice has to go somewhere! white brothers and scotts performance both sell battery eliminaters. they're about the size of a 35mm film can. i used one on a drs suzuki for years. i still use my e-start so i am not sure what is required to fill the hole from the starter. shouldn't be to involved. also.....i just got back from picking up the 5tj1551201 idler gear. they've gone up to $58. :)


Removing the battery does NOT waste the stator. Removing the battery is the same as having a charged one inline. The stator will only deliver if a current draw is demanded.

I can unhook my stator wires completely, it doesn't hurt a thing?

I obviously missed sometihng... what does that idler gear do?

Idler gear 1 is the gear between the starter and idler gear 2. Idler gear 2 turns the starter clutch which starts the bike. If you remove this gear it mechanicaly removes the starter from the fly wheel. It is supposed to turn clockwise and counter clockwise but a factory defect allows it to only turn one way (or with 80+ pounds of torque), thus spinning the flywheel off of the rotor causing the woodruff key problem. Get a working idler gear or removing it will fix the infamous "WOODRUFF KEY PROBLEM!"

Sorry to bring this up again.

I've heard all the work around for this problem: replacing key, loctite, re-torque, duct tape, voo doo, acupuncture, etc...

Can a properly functioning idler gear be obtained? I haven't had mine shear yet, but I'm not looking forward to it happening... I want to have confidence that I am never going to have to push.

The basic problem is the dealers. They WILL NOT LISTEN to anyone and make it seem as if each individual is unique with this problem. All of this info is a waste because the dealers believe that us, the consumer, is wrong about the problem and the internet is full of lies, and Yamaha would tell them about the problem if it was real.

The basic problem is SOME dealers.. There are some good ones who haven't had many problems..Some of them don't read the info they get from Yamaha and /or don't know what it says and/or don't do what it says.. I'm not making excuses for Yamaha, they ought to be B----slapped individually and I'd love to do it, but I'm speaking from some experience here/ :):D

I'm confused. If we take the gears out of the starter, how's the thing going to work? I love simple solutions...I also love my starter. What gears? Pics? More info?


I just picked up an '04 WR450. It appears that they changed the starter drive this year by replacing the 1st idler gear with a"torque limiter" (sort of a slip clutch). It looks quite different than the old idler gear. The engine cover has been modified to accept the extra width of the limiter. Looking at the drawings in the manuals it looks like the limiter might be able to be used in an '03 if the engine cover is replaced as well. I'll take a look at my friends '03 this weekend and check it out.

Keep us posted. That sounds like the long term solution I am interested in...

That sounds like the long term solution I am interested in...

And Yamaha should pay for it!

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