Transmission stuck in gear after mating case halves | GTAMotorcycle.com

Transmission stuck in gear after mating case halves

tricky

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This is a copy of a post I just made on yamahaenduro.com - but I figured maybe someone here may be able to advise

Hey everyone,


I've been working on a 1975 DT400 engine for a while now.


Every time I join the cases, I can't shift gears. It's stuck in a gear. The shift drum has a few degrees of loose play and then its solid on either end.


I can rotate the output shaft all day while trying to turn the shift drum, but it won't budge.


This is my 2nd time splitting the cases, going through the transmission parts diagram, making sure it works, then joining the cases. Before the cases go together, it shifts through all the gears as I rotate the output shaft. I can't seem to replicate the problem with the cases split.


I noticed this time, while splitting the cases after another failed attempt, that it begins shifting gears once the cases are split a quarter inch or so.


Does anyone have any words of wisdom? Am I missing something basic, or has anyone else ever experienced this?


When the urge to drop kick the bottom end subsides, I'm gonna remove the left side crank bearing so I can mate the cases temporarily to try to figure out what's happening.
 
The only thing I can think is that the mainshaft/output shaft support bearings aren't properly seated in the cases, causing everything to bind ?
 
Both the main shaft and drive shaft bearings are held in place with retainer plates (#14 and #29), and both bearings have retainer clips as well (#13 and #31), which is why I assume the bearings must be seated properly. I think you're right though - seems like something isn't seating right somewhere. I'll be sure to double check the bearings.

wyrqDtR.png
 
In case anyone down the road ends up here with similar trouble, here is the answer I posted in my build thread:

The culprit was the stopper bolt, parts 9 through 12. It helps the shift drum stay in gear. The assembly was so gummed up that the stopper was stuck, and wouldn't allow the shift drum to rotate at all.
yamaha-dt400-1975-usa-shifter-1-250bc-400bc_bigyau1068c-7_1872.gif



I popped it in the vise to compress the stopper down. This photo was taken after I compressed the spring. I used a small socket to compress it even farther, at which point when I released it from the vise the assembly came free. I was able to clean it up and reinstall it, and the bike seems to shift fine now.
4yc9jtU.jpg



I removed the left side crank bearing to troubleshoot this issue, so now I have to permanently join the case halves (for hopefully the last time).


The stopper sits here on the bottom of the engine. Until today, I just assumed it was some sort of drain plug and didn't give it a second thought. Now I know!
C1w9oSD.jpg
 

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