Gearing Problems

Hello Everyone, my name is Robert and I own a 2003 YZ450. I've been having some issues with 4th gear and its really getting irritating. A few months ago I was out riding in the Palm Desert and while doing a hill climb 4th gear would slip like a bad clutch in a manual tranny car. I did alittle research and a local shop told me to start by changing the clutch pack. When I pulled the old clutch out I couldn't tell any difference between the new and the old plates so I decided to go alittle further and completely tear down the engine. Once the engione was completely apart I still couldn't see and excessive wear or broken gears so I put it back together. I had a few problems reessembling the engine that took me a while to get worked out. By mistake I didn't line up the oil pump gear with the clutch basket gear and ended up breaking the oil pump gear. This in turn caused the gear on the intake cam to spin a few degrees causing the timing to be off. After replacing the intake cam the timing was perfect and the bike would run like a champ. However, now when riding in 4th gear the bike would lundge hard. So again, I took the engine back apart this time replacing the main gear axle and 4th pinion gear. Now, after never taking the gears apart before and putting the transmission back together the best I could remember, I can't get the bike to shift into neutral and since it won't go into neutral I can't start the bike either. So, my question is has anyone had any problems with 4th gear that was more than just the clutch pack and what should I do to get neutral back. Anyone information would be a tremendous help. I really don't want to have to take the engine into a shop. Thanks

Robert

By mistake I didn't line up the oil pump gear with the clutch basket gear and ended up breaking the oil pump gear. This in turn caused the gear on the intake cam to spin a few degrees causing the timing to be off.
Unless you are saying you ran it without oil pressure, this isn't related. The cam sprocket slipped because the cam seized, which could either have been from lack of oil or from improper torque at the cam caps.
After replacing the intake cam the timing was perfect and the bike would run like a champ. However, now when riding in 4th gear the bike would lundge hard. So again, I took the engine back apart this time replacing the main gear axle and 4th pinion gear.

What should have been replaced was the 3rd and 4th pinions, and the #2 shift fork. Your problem was caused by worn locking lugs on the sides of these two gears.

Now, after never taking the gears apart before and putting the transmission back together the best I could remember, I can't get the bike to shift into neutral and since it won't go into neutral I can't start the bike either. t
Will it not shift into neutral while running only, or not at all, even with the engine shut off? If it's only with the engine running, it's a matter of the clutch dragging (not releasing completely enough). That should improve as your new plates break in, but it also may not be adjusted right. If the bike can't be shifted to neutral with the engine off, you have made an error in assembling the trans/shift cam/linkage somewhere.
What should have been replaced was the 3rd and 4th pinions, and the #2 shift fork. Your problem was caused by worn locking lugs on the sides of these two gears.

Will it not shift into neutral while running only, or not at all, even with the engine shut off? If it's only with the engine running, it's a matter of the clutch dragging (not releasing completely enough). That should improve as your new plates break in, but it also may not be adjusted right. If the bike can't be shifted to neutral with the engine off, you have made an error in assembling the trans/shift cam/linkage somewhere.

Okay, thanks for the help. I will order the 3rd pinion and the #2 shift fork before I tear back into the engine again. As for the shifting issue, the tranny will not go into neutral at all. I'm thinking that maybe I twisted the shift cam alittle and maybe I just need to reposition it. Thanks for the help

Robert

The problem (the original one that is) was either... or a combination of a few of.... at least two gears (not familair with the exact layout of this trans, I work on mainly sportbikes but the trans is basically the same, so im assuming grayracer is right) the shift fork that moves one of those two gears, and POSSIBLY the shift fork shaft that fork is on. As he said it is caused by the dogs on the sides of the gears slipping. This is usually caused by a bent fork, or a bent shaft. But when one goes the other usually suffers too.

When you go back in, replace all three shift forks... there not that expensive, and both shifter shafts, and the two gears you need.

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