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dave03yz

4th Gear...Not So Pinned!!!

21 posts in this topic

Sorry if this takes a while to explain, but I think I should mention everything I can. I ride an '03 yz450, which is pretty much stock other than the gearing which is 14/50. A few rides ago I noticed my bike "surging" when I would ride a wheelie, and figured it was a float bowl level or carb/fuel issue. The more I rode the more this "surging" occurred, and now it was happing just riding at part throttle in 4th gear and 4th gear only. A buddy of mine has an04 yz450 and his bike started doing the SAME thing. :applause: It feels like you are feathering the clutch as you ride, but, obviously you're not. So I am attributing this to a problem with 4th gear, as the problem only happens in 4th. This surging got so bad I couldn't even ride in 4th with out the bike surging. As of tonight I have taken the engine out and split the cases and inspected the gears, dogs, shift forks and shift cam. The left shift fork has some grooving in it from the teeth on 3rd gear and the edges on the dogs on 3rd and 4th gears have rounded edges and what looks like slight chipping at the upper corners. Also the surfaces on the 3rd and 4th dogs where each contacts the other gear is smoothed and looks to be wearing, possibly excessively? I'm assuming 4th gear is popping in and out of gear very rapidly causing the surging. :ride: Has anyone else had this problem? Or has anyone fixed a buddys bike with a similar issue? And if so what parts were replaced?4th gear, shift fork? Thanks for taking the time to read this, hope this is enough information for some help. Oh, and I'm pretty sure my short gearing (14/50) is the culprit, such high RPM's for so long in one gear...

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The exact same thing happened to my bike about 4-5 weeks ago. I have a 2003 YZ250F, so its a 5-speed, and when i was tapped out in 5th it would "surge". When it first started happening, it wasn't so bad. I thought it was the clutch, so I put a new one in. That didn't work and then I finally realized it was only 5th gear. So I brought it to GB Works to have them do the work. I would have liked to do the work myself but I have never split cases and i'm looking to sell the bike soon, so i didn't want to mess anything up. The bike has been in the shop for about a month. The guy doing the work said it needed 3rd and 5th gears as well as a shift fork. The bike has been ready to put back together for awhile, however 3rd gear is backordered from yamaha , so i've been stuck riding an old 426 this past month.

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I had the same problem too with my 426... I needed to replace 3rd, 5th and the shift fork. It did feel like the clutch in the beginning so I changed that but it didnt help. I wonder how many clutches Yamaha sold to people that really needed a transmission.

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In regards to your why did this happen question; I don't think riding in that gear would cause the problem; but shifting without the clutch certainly could contribute to the problem, especially if you have been doing that for some time. When you shift without the clutch, especially while under power, those gear dogs have to get together with the gears while there is an enormous amount of pressure on the parts. This can greatly accelerate the wear on all parts involved.

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If you shift without the clutch but are cutting the throttle for the split second that it takes you to shift than you shouldnt have any excessive wear on the transmission as far as i would think, but i could be wrong. Backing the throttle off allows everything to syncronize just as pulling the clutch in would do, and should be just as smooth as shifting with the clutch. Certainly if u are doing clutchless shifts w/out dumping the throttle at all i could see this causing issues, because as you said there is a tremendous amount of pressure. Then again this is all just my opinion and i may be wrong.

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Here's what the damage looks like. I ended up replacing damn near all my gears in my 2000 as well as both shift forks. I may have went a little overboard, but I do not want to split the cases on that pig again anytime soon.

IMG_6429.jpg

IMG_6425.jpg

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LOOKS IDENTICAL TO MY HOW MY 2ND GEAR WENT OUT ON MY 426 !! lol . i got a question for u guys. the only time i clutchless shift is when i am riding wheelies . i do somewhat let off the throttle. do u still think its bad for it? and i have been noticing that it has been wanting to pop out of 5th and back into 4th when riding wheelies. is this a sign that my 5th gear is about to go out too? it looked fine when i replaced 2nd a couple of months ago

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Well, like MOST people that ride I do SOMETIMES shift without my clutch and I do let off when I do it. But, the bike is 3 years old now and I do ride it a bit, so I bet that it has just been adding up. I looked at the gears as they ride on the shaft and reinstalled the shift cam and fork to see how they move together along with the gears. It looks like there is just enough slop in the shift fork that when you shift into 4th with a load the fork moves back a little and causes the gears to slip, causing the grooves FROM 3rd gear on the shift fork and the excessive wear on the faces of the 3 & 4 dogs. Also there is some grooving in the support hole that the shift fork rides in from caulking at a slight angle. I'm pretty sure a new shift fork, 3rd, and 4th gear will fix it, but I'm going to a few shops first to ask some questions. I dont feel like splitting these cases again. In the 426's 5 speed, do 3rd and 5th ride next to each other on the shaft with a shift fork in between?

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hey man dont worry. i almost freaked about that too. the ahift forks only move because the other half of the case isnt on there yet. your talkin about the shift forks being able to move at the end's right? well once the other half of the case is on there those wobblie end's go into their own slots on the other half of the case and they CANNOT move,trust me take a look at it.

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I know the other end of the fork goes into the other case, but I'm talking about when the fork is pushing 3rd into 4th gear so it is in the case side closest to 4th gear(right side, kick start side). That case is giving it the most support at that point, and the fork walks around just a hair. I'm not saying i need a new case, just that thats the problem and some new gears and a fork with tighter clearances SHOULD take care of it. I hope...

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I have this same problem on my '01 426 SuperMoto, wide open in fifth and now sometimes fourth the bike surges like I'm fanning the clutch. I adjusted the clutch abit, then I adjusted the main jet (I thought it may be carb related), no difference. After reading this thread it's clear that it is the gears that are worn. You can see in Pincushions photos where the gear slips and then grips causing the surging. I drained my oil to investigate and when I looked at the oil filter sure enough there are metal shards in the folds of the filter.

I have the workshop manual and it definitely looks like a very challenging project. Besides the clutch tool are there any other specialized tools needed to split the cases? Any useful tips or pointers would be appreciated.

Wish me luck!

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I have this same problem on my '01 426 SuperMoto, wide open in fifth and now sometimes fourth the bike surges like I'm fanning the clutch. I adjusted the clutch abit, then I adjusted the main jet (I thought it may be carb related), no difference. After reading this thread it's clear that it is the gears that are worn. You can see in Pincushions photos where the gear slips and then grips causing the surging. I drained my oil to investigate and when I looked at the oil filter sure enough there are metal shards in the folds of the filter.

I have the workshop manual and it definitely looks like a very challenging project. Besides the clutch tool are there any other specialized tools needed to split the cases? Any useful tips or pointers would be appreciated.

Wish me luck!

Never used a clutch tool.... You need a flywheel puller and a torque wrench (in/lbs and a ft/lb unit) And misc hand tools. If you are fairly mechanically inclined and take your time it is a simple job. Just take your time and look at everything before you take it apart and as you continue to disassemble. :applause: Good luck. :bonk:

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Never used a clutch tool.... You need a flywheel puller and a torque wrench (in/lbs and a ft/lb unit) And misc hand tools. If you are fairly mechanically inclined and take your time it is a simple job. Just take your time and look at everything before you take it apart and as you continue to disassemble. :applause: Good luck. :bonk:

Are you saying that it is possible to remove the clutch assembly without the special tool? Or am I missing something? I know you need a flywheel puller for the crankshaft. I have heard people say that an air impact ratchet will remove the clutch bolts without the need for the special clutch holding tool, is that how you guys have done it?

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It is possible, but not always reccomended. Another member here used an aluminum wedge to prevent the clutch basket from rotating adn I'll just say he ended up with a new clutch basket. The tool isn't too expensive. At least not as expensive as a new basket.

If you can follow instructions then you can swap the gears. I had no experinece prior to changing mine and it's been since 4 months now without a problem :applause: I will reccomend taking lots of pictures though. Sure helps with reassembly.

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Are you saying that it is possible to remove the clutch assembly without the special tool? Or am I missing something? I know you need a flywheel puller for the crankshaft. I have heard people say that an air impact ratchet will remove the clutch bolts without the need for the special clutch holding tool, is that how you guys have done it?

You can use a strap wrench and a impact wrench to remove the clutch basket.

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Think back and try to remember if you ever fell on the shifter side to the point that the shifter made contact with the ground.....Im not saying that caused your problem

but a bent shift fork can wear the dogs like yours and eventually make them pop out of gear under power.......thats been my experiance anyway......

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