426 gearbox help needed

[klimtachakka]

Hi, 
As of yesterday my gearbox went to shit,  started to find false neutral everywhere, dropping out of gear, hard to find gear.  

(I have been working on this mf to get it road legal and was at the place where they do all tests, but they refused because it was snowing... So yesterdays expectations went from having a road legal bike to having to split the cases... )

Currently I have removed the engine from the bike because I think I need to split the cases to sort this out.   So what am I looking for when I have the gearbox out?  
Is here some guide or walktrough when splitting the cases?  Do's and dont's?   Pictures describing the process would be a plus.

I have removed the inner clutch cover and looked at the transmission mechanism there. It looks like for some unknown reason that sometimes when you shift the shift shaft will stop and not move until the shiftstop and this will cause a false neutral I guess... ?       

Help needed,  never done this type of voodoo magic thingy before. 

[grayracer513]

Shifting with a dead engine requires at least one transmission shaft to be rotated so the locking lugs on the gear sides can align with those into which they engage.  Typically, the corners of the lugs become battered round and they lose the sight undercut built into them so that under a load, they push away from each other instead of locking in.  That's most of what you'll be looking for, along with worn shift forks.

Download a free manual:

https://redirect.viglink.com/?format=go&jsonp=vglnk_148657023339912&key=fd4d0c8927dbf2331e83bbda32ac7c21&libId=iyx5j3yf010004is000DLjrxb1koxceix&loc=https%3A%2F%2Fwww.thumpertalk.com%2Fforums%2Ftopic%2F378677-common-threads-look-here-1st-mods-maintenance-common-issues-and-faq39s%2F&v=1&out=http%3A%2F%2Fwww.yamaha-motor.eu%2Feu%2Fservices%2Fowner-manuals%2Findex.aspx&title=Common Threads%3A Look here 1st! Mods%2C Maintenance%2C Common Issues and FAQ's - YZ 400%2F426%2F450 - ThumperTalk&txt=http%3A%2F%2Fwww.yamaha-mo...uals%2Findex.aspx

https://redirect.viglink.com/?format=go&jsonp=vglnk_148657024680913&key=fd4d0c8927dbf2331e83bbda32ac7c21&libId=iyx5j3yf010004is000DLjrxb1koxceix&loc=https%3A%2F%2Fwww.thumpertalk.com%2Fforums%2Ftopic%2F378677-common-threads-look-here-1st-mods-maintenance-common-issues-and-faq39s%2F&v=1&out=http%3A%2F%2Fwww.yamahaownershandbook.com.au%2F%3Fr%3D0&title=Common Threads%3A Look here 1st! Mods%2C Maintenance%2C Common Issues and FAQ's - YZ 400%2F426%2F450 - ThumperTalk&txt=http%3A%2F%2Fwww.yamahaown...ook.com.au%2F%3Fr%3D0

[klimtachakka]

Thanks,  allright so follow the manual and everything will be fine I guess.  
 

[zibbit u2]

Yep, take your time, and look very closely at all the adjoining gears.  Load each gear against the dogs of the the next gear and see if they're trying to force each other away, rather than locking and holding steady. 

If you're not comfortable or well enough equipped with special tools to do a complete teardown and inspection of the motor, you might be better off sending the motor into Yamaha shop to have them do it for you.  There's a hell of a lot of moving parts inside these motors, and it can get really expensive fast if you don't know what your doing.

[klimtachakka]

Before I have had the cams, clutch and flywheel of. Would I be needing any other special tools now when opening up this can of worms?

[knuckleduster271]

Ive never worked on a 426- my 450 didn't take anything special other than a flywheel puller and a torque wrench. 

I split the cases fairl easy usuing a large screwdriver (theres castings on the outside of the cases. Once you get them somewhat apart use a soft faced hammer and tap the flywheel end of the crank with the engine laying on its side having an extra set of hands holding it a few inches above the work space. 

[klimtachakka]

First of all, thanks for the tip about the manual. A very good read and good trouble shooting tips.  After fiddling with the engine some and having a cold one I noticed a loose bolt.  Checked the manual, hmmm that should not be loose, 30nm is NOT loose.
It was the bolt holding the shift drum thingy in place, so this would often set the shift drum between positions.  At least I hope so....
Does it makes sense that this loose bolt could give me false neutral and hard finding gears like almost everywher.   The bike went from working flawlessly to this shit in about 30 minutes...



 

[grayracer513]

Be careful relocating the segment wheel onto the shift cam.  Note the locating pin.  This pin can be pushed in flush with the cam if misaligned on assembly, and you would need to split the crankcase to correct that.

[klimtachakka]

Be careful relocating the segment wheel onto the shift cam.  Note the locating pin.  This pin can be pushed in flush with the cam if misaligned on assembly, and you would need to split the crankcase to correct that.

Thanks for the info. I have put I together and it works on the bench. Will have to see later when I get the bike together if I &%$#@!ed it up or not.