photos.app.goo.gl/izB3Ek3AwztSQrhXA

I am getting ready to put the cases back together and I’m not sure if I need to orient the transmission in a particular way so that it is in neutral. Please see photo in the link that shows a legend mark on the drum shifter. Does this mark have significance in the way it is aligned ?

Thanks for any help.

Yes it has significance.  No, you technically don't have to assemble in a neutral or any specific gear.

There are marks (not seen in your photo. under circlip/washer) to align the sector plate to the shift drum.  It can be installed 180 degrees out of time.

The mark you are referencing is used to adjust the shift linkage "claw" centering with trans in first gear.  See the "78 DT125E DT175E Service Manual" in Tech Library for instructions (I avoid the similar multi-language "MX" manual, I find it harder to read but should work too).  (If you didn't mess around with the eccentric pin, adjustment probably isn't needed, but should be checked)

 

Another note, If you want to assemble in neutral, again, not "required" but what I do, on the other end of the shift drum (sprocket side) there is a small rivet (DT175) or the hole for the rivet on most IT175's that is straight up on the top when in neutral.  (The rivet activates the neutral switch on the DT, blanked on the IT)

Just to the rear of the rivet/hole is divot that the detent ball drops into with trans in neutral.  You can look down the hole the spring and ball go into to see this divot.

I find it MUCH easier to assemble the trans into the right side case so I just point the rivet (or rivet hole) on the left end of the drum straight up as I assemble.

I actually had some pics saved...

Shift sector "timing"


Linkage adjustment:


 

Good stuff, Mark.
Thanks for the explanation and the write-ups.
One more question, I’m not sure how I can tell if the transmission is shifting through all 6 gears properly. Everything is moving freely although it takes some jiggling around of the shift forks to get things moving sometimes.

Thanks

You have to spin shafts to get it to shift.  Never easy to get it to shift on the bench.  I learned not to worry about it and they've always worked fine once running. 

That makes me feel better. I’m fairly certain that I have the transmission back together correctly.. Time will tell.
I appreciate your expertise.

Regards 

I used to be afraid of splitting cases because of the trans. 

I've done a LOT of the AT/CT/DT/IT 125/175 transmissions.  The earlier ones are trickier because they have a shim and little rollers on the shift forks that can fall out.. 

Once you get to 1977, they are super simple in terms of no little parts that can fall out...  I have not been able to screw up one on these...  the fork pins only fit in the drum grooves one way and I've even purposely swapped the shift forks (one is different) and it just won't go together at all or it locks up.  It seems the design is somewhat Mark-proof and only goes together one way which is not always true.  Usually if something can possibly be assembled wrong, I've done it somehow.    

(I haven't tried removing all the individual gears from the shafts and swapped them around in every possible combination but there are enough differences that I think even that is not possible)

You can assemble the linkage wrong...  like having the sector 180 degrees out as I mentioned and then you only get two gears if I remember correctly...  but that's an easy fix that does not require cases to be split.  (And yes, I've done it)