YZ 450 4th gear issues

I went out for some MX practice on my '04 YZ 450 yesterday afternoon and was going through the gears on a straight. All was well until I shifted to 4th, and it started hesitating and making a slight grinding noise and felt almost as if the clutch was slipping (definitely not the clutch though because the other gears are fine). I tried 4th gear several times after that, and something is wrong. Every time it hesitates, barely accelerates, and makes the grinding noise. Is 4th gear stripped or worn? If so, is it a pretty serious repair (i.e., splitting the cases)?

Yes, you have a damaged 4th gear on your hands, and yes, repairing that means you have to split the cases. Not real expensive, though if DIY.

Yes, you have a damaged 4th gear on your hands, and yes, repairing that means you have to split the cases. Not real expensive, though if DIY.

This may sound crazy, but I wonder if I could get away with just changing to a different sprocket to gear the bike a little taller in the meantime. Being a 4 speed, do you think this would work since there are only a few straights that I even hit 4th gear? Would it wear anything out prematurely? Thanks

If you stay completely of 4th, maybe. I don't advise it.

Yeah, I can run the track without accidentally shifting to 4th. I hit most of the big jumps in 3rd pinned anyway, and that is my biggest concern (i.e., leaving the face of the jump safely). I might run it like that for a couple of months and have the top end rebuilt when I get the gear fixed.

Thanks Gray

I might run it like that for a couple of months and have the top end rebuilt when I get the gear fixed.

That's really not a good idea. Your engine lives on the same oil where all of whatever loose fragments of 4th gear went. Don't say I never mentioned it.

That's really not a good idea. Your engine lives on the same oil where all of whatever loose fragments of 4th gear went. Don't say I never mentioned it.

I guess I'll go ahead and take care of it then. Thanks for the heads up Gray.

i think i have the same problem on my 98 yz400....it went into fifth gear fine and didnt grind really but if i throttled up too fast it popped out of gear and back in..or more like a hesitation like you said...i got the crankcase apart the other day...and the gears arent terribly worn but the shift fork looks like it got dug into by the groove on the gear but the teeth and dogs on the gears all look fine...anyway good luck with your rebuild and make sure to inspect all movement and clearances as well as wear....

... the gears arent terribly worn but the shift fork looks like it got dug into by the groove on the gear but the teeth and dogs on the gears all look fine...
Trust me when I tell you that if you do not replace the 5th and 3rd gear pinions (on the main shaft) to correct this problem, you will be taking it back apart. :doh:

yeah...im probably gonna change out all four pinions and the faulty shift fork...would it be a good idea to change out the spacer washers with the circlips or no? thx for your help.

yea dude, that is a case splitter. don't trip, the hard part is taking it apart, then you'll have to get it together again. i dont know much about the gears , but i do know you dont want any more metal shavings in there. you probably will have to clean up enough already. if you continue to test ride, you can jeopardize bearings, and yer oil pump, an stuff.

ya this exact thing happened to me awhile back. i had my race mechainc replace all 4 gears and all shift forks.

Well not to sure if I have the same problem as you do but sure sounds similar.

I have a 2002 YZ426f.

My last ride my 4'th gear started surging on me I guess the best way to describe it is. It didn't bog out, surged and rpm kinda shot up and down and still accelarated, not smooth by any means and surging/rpm shooting up. Almost feels as if chains slipping or clutch is?

My clutch I don't think is the problem since it only does it in 4th gear. It's at the point where even a tiny bit of throttle for 2-3 seconds in 4th and it starts jerking/surging. Every other gear is still 100% fine.

I am not very mechanically inclined. What's the best way to diagnose the problem and get it fixed? Should I drain my oil see what's in there and in the filter? I am done riding it until I get this figured out and fixed. I'll probably end up bringing it down to a local mechanic shop I think.

What do you think it will cost me on average? If it's a 4'th gear that needs replacement? Sucks considering I just bought the thing and have probably about 20-25 hours on it.

p.s I have ridden it twice with this problem, first time was out camping went for a quick 5minute ride hit 4th once and felt that surge when WOT, so started heading back to campground and coming around a corner gearing down to 1'st my clutch cable snapped. Got a new cable, replaced it, went for a ride and noticed the same thing in 4'th and didn't use 4th much at all. Got to the point as I described above doesnt need to be WOT just a tiny bit and starts surging/skipping. No weird sounds at all in any gear and no problems with any gear besides 4'th all the power and balls still there. Any help is greatly appreciated.

Well not to sure if I have the same problem as you do but sure sounds similar.

The way you describe it; jerky, worse the more load there is on it, only in one gear, and feels a chain jumping over sprockets, it's almost certainly a fourth gear problem.

In a 426, that means at minimum, the third and fourth pinion gears (on the main shaft), and the fork that moves the third pinion.

Thanks for the reply gray. So what am I looking at for price in parts?

Going to phone the dealers when I get some time off work in the next 3 days as I am working through the hours they are open.

You will definetely be lookin at around 30 - 70 bucks per gear that needs replacing around 35 - 45 per fork... + seals and bearings you may need....and labor...idk about your area...but around here in central california labors usually anywhere between 60 - 90 per hour...id recommend haveing it done by someone though... if you have little mechanical inclination like you said...besides ud almost certainly have to spend 100 or 2 on tools if you were going to attempt it...anyway good luck with your rebuild...oh and by the way those approximates on part prices is from cheapcycleparts.com they have most OEM yamaha parts in-stock and have an online micro-fishe parts finder good luck.

I would not ride it until you at least take it apart and observe the problem. Imagine opening your oil fill drain and dropping nails, staples, broken parts of drill bits, etc. in there and then start it and go drive around. That is probably what is inside your motor now. Its unwise to assume otherwise. A $40 fix could easily become a $3,000 fix.

Sic..

Thanks for the info quicksticks and sic. I have tuesday off so I am going to call them and check on prices and get it in there to get it fixed. Sucks though going to have to drive 4-5hrs to the closest shop lol. Sucks living out here in the north boonies. But hey the fishing/hunting/riding is awesome.

Well, talked to the shop today. They told me they will need to do a complete tear down then take a look and diagnos the problem and then go from there. Parts + Labor etc...

So he said 10hrs for the tear down labor at 98$/hr. That's pretty much a grand to take it apart and figure it out, then go from there getting parts and labor on top of that. I didn't ask how long to put everything back together once I get the gears figured out as I was so disgusted with 98/hr for labor and pretty much a grand to tear down and split the case. What a godamn shame im so bummed out and mad, I just want to ride as summers coming up. I buy the bike put 20-25hrs on it then this happens :doh:

I am just going to give a friend $200 and get him to show and help me tear it right down and split the case so I can learn myself. Then from there probably order up the parts myself from an OEM dealer I found online with pretty good prices on gears. Then I will probably end up bringing it down to a dealer to get them to put that all back in for me and put it back together. Going to look elsewhere though, I am sure I can find better than $98hr, seems a little outrageous and steep.

$85~100/hr is pretty standard, although I think the 10 hour figure should represent the total labor to tear down AND reassemble it. Tear down shouldn't actually take more than 3, although it may pay more.

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