WR 450 starter chaos

i know that the starter mechanism on the 660 raptor is prone to failing, when engine is cold has a tendency to stall, when the engine stalls it may turn backwards. sometimes this engages the starter mechanism and breaking parts. Hopefully the wr does not use the same style of mechanism.

My mechanic, after he looked at it and found the key broke. He asked if it backfired at all? I told him that it did right when it broke.

Well, if the starter motor broke the woodruff key, the timing would be way advanced, this could make it backfire.

Funny he would say this efore I toldhim what had exactly happened.


Do you think they may have just forgotten to torque the nut at the factory and this is what caused the issue?

I doubt that is the problem. In an extreme case a loose, or missing altogether, flywheel nut may lead to a woodruff key failure.

However, if you stop and think about it for a minute you will realize that once the woodruff key breaks it is only a matter of time (a few seconds??) before the flywheel nut unthreads.

The starter spins the flyweel, the crank doesn't spin, and there goes the nut... :)

Wait a minute guys. The bike back fired and sheared off the woodruff key on the flywheel. That is understandable. That is why the key is a softer material than the flywheel and crankshaft. It will break (.99 cent part) before the flywheel or crankshaft or ? (not .99 cents). That is a built in safety feature.

The thing you need to understand is that this has NOTHING to do with the starter, the starter gear or the mechanism that engages the gear. The starter turns the flywheel that turns the crank that starts the engine. If the flywheel is disabled so is the starter, obviously.

This problem could happen on ANY fourstroke, with or without a starter. Lets not blame the mishap on something just because it's new and unchartered.

I believe it has happened to the WR450 (twice?) because the bike is jetted so lean from the factory and it back fired uncharacteristically. Probably because of emission purposes. It just so happened to do it to this time during starting. Remember this bike makes a lot of horsies, so when it back fires it is changing those horsies from clockwise to counterclockwise instantaneously. Good thing only the key broke, and not the crank or rod.

All we need to do is richen up the jetting (pilot , clip, main jet) so that the bike wont back fire and cause problems. I think I may start caring an extra key or two in my fanny pack just in case.

That's good to know that the origin of this issue may possibly be a jetting problem. Curious about the woodruff key, though. I was under the impression the key was a solid part of the flywheel and that the entire flywheel would need to be replaced. Having never seen one before, I'm a bit confused. Is this part something that could be packed in a fanny pack and replaced on the trail??

There is a groove in the flywheel and a groove in the crankshaft. The woodruff key is a little piece of soft metal that goes into the grooves. It sets down into the crankshaft groove, and sticks up into the groove in the flywheel. It locks the two together.

It is the weakest part of the link between the two parts, it is designed to shear off in the case of bad things like a violent back fire.

Thanks David. After seeing some pictures of what a woodruff key actually looks like and your description I now have a much better understanding. It appears that it is something that could be replaced on the trail, if necessary. I'm feeling much better about this issue now...

I disagree David. My XR650L has 2000 miles of tough trail riding on it. It backfired many times before I got the jetting right. The starter has operated over a 1000 times. I have never had a problem with it.... What we have with the WR is a design that tries to cut weight at all cost....

Weight reduction really has nothing to do with a woodruff key failing, they are suppose to fail, that is there role in life, they break so more expensive parts don't. If they break, a person should be well aware that something isn't right and should have the problem remedied promptly. Really not a big deal in itself, the potential problems that arise from a chunk of metal floating around is another. Hopefully all that read these posts won't be alarmed but informed and take a few extra easy rides to sort out jetting if backfiring occurs.

Yeah Bamy thanks for the wild speculation :)........... Any chance you might have anything positve to add to the YAMAHA Forum?

The bike back fired and sheared off the woodruff key on the flywheel.

I hadn't considered that, it makes a lot more sense than my theory.

Starter engages flwywheel, motor "kicks back," woodruff key is lunched.

Since bikes, cars, aircraft, boats, etc. backfire all the time while starting without parts failure I would submit that Yamaha does indeed have a minor problem that needs to be researched and corrected. Replacing woodruff keys on the trail would be the pits. Possibly one of many new designs on this machine it is to be expected and doesn't rate wild speculation, calling people trolls or outright bias towards the person reporting them. Look at the troubles the new CRF had or the well know issues on KTM's. They have been found and are easily corrected.

Volgens mij zijn er hier een paar KTM liefhebbers die hier flink aan het stoken zijn, zijn ze soms jalours op de blauwe beesten ??

My Sentiments Exactly....

Bonzai :)

Als ik en KTM liefhebber was, zou ik ook jalours zijn! Ik ben dankbaar dat ik en Yamaha hebt! Nederlands...te gek jongen!

Yeah, what he said :D (I think :))


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Hey! Its the swedish chief!! Your my favorite muppet :)


Hmmmmmmmmmmm.....so what should i do, just use the kicker,

until this problem is solved ??????? :)

My Wr had about one hour on it when my key sheared.

I pulled the cover off and the fly wheel nut was backed off about 3 or 4 full turns. The key looks a little thinner

than most than most of the other bikes I have owned.Mine

seemed to have happened during starting although my bike

did backfire a few times during the ride

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