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MathProf

Replacing 3rd gear, what else should be replaced?

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My bike won't stay in 3rd gear under power. It doesn't clunk, it just pops out. :)

I'm guessing the "dogs" on the gear have sheared off and I need to replace a couple gears.

While I have the thing apart, is there anything else that should be replaced.

The bike is a year old and I was thinking about replacing the valve springs, camchain, and checking the rings.

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you'll probably find that if it jumps out of 3rd, 3rd won't be thr faulty gear!

It could well be the gear that 3rd drives off. Will my 426 it would jump out of 5th, but 3rd was the culpret. At only a year old I'd check the topend, maybe do the springs if you murder the engine every weekend. Check the valves where they seat on the head, and signs of a 'ring' or little circular dots and they are toast.

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Hamish,

That's something to think about.

I was considering disassembling the engine down to the cases and having a mechanic split the cases and determine what should be replaced.

I'm not sure I would know what to look for.

Thanks

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Check for bent/warped shift forks, or if the fingers on the forks are worn out. The dog teeth are pretty robust, and rarely break off. But if you've had this problem for a while, the dog teeth may be rounded off, or worn down.

ps: the gears and dog teeth are cast iron parts, so the have small rounded edges anyway.The factory does not do any machining or finish work to the dog teeth, only the gear teeth.

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Check for bent/warped shift forks, or if the fingers on the forks are worn out. The dog teeth are pretty robust, and rarely break off. But if you've had this problem for a while, the dog teeth may be rounded off, or worn down.

ps: the gears and dog teeth are cast iron parts, so the have small rounded edges anyway.The factory does not do any machining or finish work to the dog teeth, only the gear teeth.

not the case, sorry. I found my dogs in the bottom of the cases.

The dogs are part of the gear, and they are definately NOT cast iron!

There should be no round edges on the dogs. some of the dogs are oval, and other are square, but they all have sharp clean edges.

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Keep talking guys. I'm learning something every time you post.:)

I hate splitting cases. I never know if all the peices are going to go back together.

I know it doesn't make sense but that's the feeling.

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get a digital camera, and take pictures as you go. When you remove a shaft (any shaft) put a cable tie around each end of it with all the bearings, shims gears etc still on the shaft in the order they were removed. Very hard to make a f$%& up then. Remember that wear marks tell a very good story. If you arent sure where a washer goes, or which way around it goes, match up it's wear marks and you'll find your answer.

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I have this same 3rd gear popping out problem, and I have the engine out of the bike ready to dive in. Does anyone have a good link to a blow up pic of the internal`s, I have never done this operation before and all I have the the factory manual to go by. And any new advise would be much appreciated since I see this is an old thread but didnt want to start a new one for the same ? Thanks. 02 WR426F

Andy

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the gears are heat treated steel, the weak link will more than likely be the shift forks. Factory service manual will have all the specs on them, take your time and take pics along the way. Have lots of clean area to work on stuff, and stay organized.

Once shift forks get bent or the fingers worn, that is usually what accelerates the "rounding" of the gear dogs.

If you want a hand let me know, I am in Westminster.

I helped out a fellow Colorado rider last winter with his XR400, there's a BIG thread about it in the XR250/XR400 forum:

http://www.thumpertalk.com/forum/showthread.php?t=876724

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Thanks for the info and generous offer, I got my spare room all prepped for the project and my camera is ready, I will save the beer for when I`m done (if it works). I did a long rod kit in a `94 YZ250 once and I rebuilt a `78 XT500 bottom end also way back I`m hopping it will all come back to me when I start. I use to live in Littleton Colo.

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