Not easy!..but got it off.   Not sure if it was worth it.  Now, will be unsure how well its attached once pressed back on.  Ordered new 3rd pinion gear and a complete ready to go shaft w/gears. (have two engines, both have broken 3rd pinion).  BTW, has anyone pressed one on and it worked successfully?
 
if anybody is interested, measurement/procedures are: 

press off : 2nd (see pic below)
circlip: 5th
slide off:  3rd:

12.5mm shaft outside 2nd gear pinion to end of shaft
1mm between 3rd and 5th pinion. 

Broken teeth 3rd pinion:


Setup to remove and install: (note, 1/8" angle iron started to bend, then gear slid off rather quickly.  I had previouly heated it a bit w/torch)

 

RT325 has posted his experiences and tips about pressing 2nd gear on.

After working on large truck transmissions years ago and seeing how gears that aren't replaced in pairs often don't last very long, I've tended to buy complete good matched transmission sets on ebay.  It didn't used to be hard to find one pretty darn cheap, as little as $20 + shipping for the whole transmission.  Not sure what the market is like now?    

And to qualify, the truck trans gears that "didn't last too long" was a comparison to using a new pair versus using one old and one new mating gear on transmissions that could last a million plus miles.  And even the less optimal match of old and new gears still lasted many more miles than most of these old bikes will ever see.  

Flashback Enterprises on eBay has a few CT1 trans listed and they often accept reasonable offers. I bought a full transmission assembly for my JT project for $35 and they are only 15 minutes from where I work so I simply swing by and pickup my parts. (oh crap….I retired yesterday) Ok, it’s 45 minutes from my house.

They are a great bunch of guys over there. Check out their huge inventory and also checkout their motorcycles. I search their inventory by entering Yamaha in the search box and then I select lowest price. You can’t believe how many parts I’ve bought for $7.50 which seems to be their minimum opening bid. Kevin runs the eBay store, so if you make any offers, tell him Bill Schu referred you!

imgur.com/a/5UtBGQf

www.ebay.com/str/flashbackenterprisesinc