WR450 Starter Update '03 to '04 Part Numbers

PDBLUE said:

Well here's my 2 cents. I've had an '04 for almost 2 months now and have put about 600 miles on it. As BajaFool said we disassembled the idler gear/torque limiters on our bikes and compared (his is an '03). I do not believe there is any difference in the crankshaft taper or diameter all though we did not measure it. IMHO the problem with the '03's is not the woodruff key. That is just the symptom. If you look at the '03 starter drive it is clear that it cannot turn backwards. If the engine kicks back there is nowhere for the force to go except into the starter drive. Actually you are lucky if the key shears because if it doesn't something else is likely to break instead (there are some other posts describing this). In the '04 you can turn the crank backwards with no issue since it has the torque limiter which slips under those conditions. The lean jetting that the '03's came with aggravated the problem. I think if they had been jetted properly from the factory the problem still would have existed but it wouldn't have been so widespread across so many bikes. Basically it's a weak design coupled with poor jetting. I believe the '04 is a much better design and will probably prove to be very reliable. Only time will tell.

My question is that if the main crank starter gear is on a one way clutch how do we get a backfire to load up the starter motor drive pinion? :)

Indy, great points!! Way to think through the issue.

that is how a sprag style starter clutch works. they are very common in motorcycles that have an e-start. our cars use a bendex(sp?)style starter. when we use it a gear moves forward on the splines of the starter shaft and meshes with the flywheel.

our wr's have a system that allows the starter system gears to be meshed at all times. that is where the sprag clutch comes in. it is the one way clutch on the flywheel. when the starter turn it puts pressure on the clutch in the direction that engages the cluth and turns the crank. when the motor starts it turns faster than the starter and turns the flywheel "inside" the clutch.

if the motor should try to go "backwards", the cluth engages and attempts to go the wrong direction. sending the force back through the idler gears. the idler gear closest to the starter is two gears pressed together. there was supposed to be some slip between the two gears to absorb the shock. if there was no slip something had to give. we have a big flywheel. if we are lucky, the flywheel key goes. thats what they do.

i work for a large machine tool company and i can tell you, it would be very hard to manufacture a pressed gear assembly that would slip the same each time. almost impossible to make several thousand that all slip at the same amount of force from a pressed assembly. the engeneer i showed it to laughed. if you have one in tolerance, no problems. if it's out just a little bit, you have a problem. that is why the new idler gear assembly is a spring loaded part. it was adjusted at assembly and will slip the same everytime. the yfz450 atv has used one from the beginning.

sorry this ended up so long. i kind of get going when i get into stuff like this. my boss just shakes his head.

mtrablue don't apologize for being long on that, thats great info. So if I take what you said correctly, if we got one that was in tolerance we shouldn't have a problem, if we didn't we will probably have had or will have problems. That sounds kinda like what has been happening.

Now to add a little more to that, it appears some shears may have been because they flywheel wasn't torqed correctly from the plant.

This is great stuff guys. Thanks for putting your thoughts down here.

most, if not all, of our manuals have a sticker in them over the original torque specs. did they change them that much? i have a cr based cre and the manual calls for 40 ft lbs for the flywheel nut. the wr calls for 47. thats not that much more. if i remember right, there was talk that some of the wr's came with nuts torqued to as little as 28 ft lbs.

ya know, we all get going pretty good when the flywheel key/starter issue comes up. even the owners with no problems. can you imagine if a hand full of us got together around a camp fire with a few beers. we'd chase everyone else away!

Great answer Mtrablue the sprag clutch makes sense. :D That means the 04 upgrade parts are worth putting in the 03's and I did not waste my money. :) I think 50 or 60 ft-lbs is the torque spec on the flywheel. There was a print error in the original manual and a loose page was supplied to address the issue.

Indy, I have had two sheared keys and one new crank and flywheel and the one-way clutch on the flywheel works fine and has not been replaced.


I'm getting ready to order the new parts and called www.powersportspro.com they have a promotion going on for 15% off right now. Figured i'd pass it along :D

EDIT:I did have to call them for a few of the parts because their site says it can't find them all :)

OK everyone. Here they are! And yes, they do retrofit from the '03 to the '04.

5TJ-15560-00-00 Torque Limiter

4GY-15521-00-00 Shaft for inside the Torque Limiter

5TJ-1549B-00-00 Side Case Cover for the Torque Limiter

90201-105A8-00-00 (2) Thrust Washers for the T.L.

5TJ-15411-10-00 Side Case

5TJ-15451-00-00 Side Case Gasket

Total $345.65 Retail


I got all the parts but the torque limiter pinion assembly came with a shaft and the shaft listed above came with a larger diameter. Not sure if we need the shaft part listed above. Can anyone verify this? Jeff? Thanks

I am pretty sure we will need a bushing pressed in to the cases for the other end of the torque limiter shaft since it is smaller in diameter on both ends. I dont want to take it apart and not have all the parts ready. I was planning on doing the upgrade next weekend. Jeff in Eugene, OR any thoughts based on your original 03 to 04 comparison?

I just received all of these parts that are on this list and the shop did a fix on another bike friday with the exact same parts and everything went fine.When i picked up the parts the parts guy told me to wait until saturday to tear mine apart just in case they got in to it and had to order any other parts.I checked and the parts on the list are all that you need.


cracked side cover


04 starter gear

smaller diameter bushing in new side cover f9e698af.jpg

Where does the large pin go?

I'm not sure why but it replaces the old shaft that that holds the idler gear!Right where mine broke in the pic.I will probably replace the parts this week,I've gotten used to kicking the bike now maybe i should just hold on till summer when it gets to hot to kick it.

My dealer has been great,the parts manager called yamaha and he said that they where going to give me a discount.I only paid $150.00 for all the parts!! :) But that might just be the dealer helping me out.

indy, if the shaft is the 4gy 15521 00 00, i beleive that is the number for the shaft that the '03 idler gear rides on. that number matches the '03 part number on the yamaha web site parts list. the smaller idler gear may ride on it also. i couldn't find a part number for it.

Thanks Mtrablue. :) In the original post jeff said to order this shaft but I dont see why I need an 03 shaft. But now I wonder if I need another bushing for the other end of the smaller shaft. If I dont get a response from jeff I will have to tear into it and figure it out. I hate the manual blow apart drawings they lack so much detail and they have parts all over it and you can see where they go sometimes. Thanks for everyones input.

You won't need a bushing the new side cover has a smaller diameter bushing already in it from yamaha.As for the small shaft it is already installed in the new 04 gears . :)

Thanks. I will retrofit this weekend and report back to this post on the results. :)

Glad to hear the new parts will work.I have been waiting for a couple of weeks now for all the parts to come in. Two of the parts on the list are on backorder until Feb. I was holding my breath until I heard of somebody fitting the new parts to their 03.

Will this repair involve pulling the flywheel :)?

I would consider doing this repair but I have had the TSB performed by my dealer with the lapping and locktite and would feel reluctant to disturb it. I can only imagine how hard that flywheel will be to free up. I assumeing I free it up and get it off, will that mean it will need to be lapped and locktite reapplied :D. I just don't feel confident about that part of the task. The mechanical nuts and bolts part I am ok with, it's just the relapping and locktite part.

Smoke :D

I dont think the flywheel needs to be pulled.

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