In the process of replacing worn gears and I thought it was be easier to replace the main axle then reuse the old one.

I've purchased two on the cheap and noticed that they have both vertical indented machined sections where the fifth pinion gear would rotate. 

I have pictures of both here photos.app.goo.gl/sLPBh8m5KQWQzdK77

Can someone tell me if these sections are supposed to be there?

 

I mightve mucked up below. I gott confused by the end haha with links open along the search bar of mine.

Here's another one NOS with gears including the pressed on end one if you want to start a collection.
Strange thing though the part number shown is for the axle only but anyway.
eBay item number:364123705180
www.ebay.com/sch/ebayadvsearch

This one below has 11 on center number but part number for the CT3 axle on cmsl parts has 01 in center number
eBay item number:192387574065

I tell a lie on cmsl i see two main axles 01 & 11options.
Confused blimey i am now!! is it a difference between 125 & 175 & if so--why. Might be Relieved there to let oil under it but thats never been a problem anyway.
www.cmsnl.com/yamaha-ct3-1973-usa_model8420/partslist/B-11.html

Hmm, thanks.

The one listed on cmsnl also has the same issue.

I will dismantle the original when I can get access to my hydraulic press and compare.

Often they make small changes and/or improvements to parts.  No need I can see to overthink this one. 

Oh... cool.

Thanks Mark.

 

Yep can see the modified bits in the links 'like your' but did wonder if it's between 125 & 175. Maybe I'm repeating myself (getting old). But what I wanted to say 'is' & I'm sure you'll be onto it--is when pressing on the gear it has no limit. I used to just smack the press somewhere when close to get incremental movements until it lightly nipped the feeler blade as easy to go too far & lock it against whatever gear it is--be 5th big gear I guess. Had those gears come loose on ya my V90 scooters when new, 3 speed 'crash box sort of' with no auto clutch release between gears. Just a bad batch of machining at the factory in "72-ish & so they sent them all to NZ haha.

Thanks for the advice. I took an old car door shim that has a U opening and sanded it down to match the gap in the
between gears on the original. Hopefully I can remove it after the gear in pressed on,

Just measure the clearance on the original if not dismantled yet.
Not trying to scare you but if you don't go close enough--probably by quite a bit--the cases might not match up as lack of end clearance for the shaft between the crankcases, plus get less engagement on 5th gear.
& obviously if you go too far & run into the 5th gear wheel it'll lock the 5th gear wheel solid.
Not sure what a car door shim is but guess it's to tilt the door angle. I'm only talking feeler gauge 10 thou or so clearance. Might be an official measurement somewhere but not sure where to look.
All the best.

I added a photo of the door shim to the google album with the photos of the axle.

Did remove the gear over the weekend and found that the original axle had the same machining as these. So I wasted everyone's time. Sorry.

Before I install, I wanted to confirm the spacing between 2nd and fifth. I came across an entry from the Clymer Yamaha 80-175cc Enduro & Motocross 1968-1978 - Service, Repair, Performance, 3rd Edition that specified that the gap between the second and fifth gears should be .002" or .05mm.

Does that sound right?

That's good info to know, so just running clearance & enough gap to let it happen & get oil in the gap.
I've never seen it written.
I used to oil them--shaft & gear to press it up, & as i said somewhere preload the press when getting close & bang the press bed to shock it so it will move incrementally when getting close.
Mind you there's a fine line between preloaded & one pump too much then BANG--bugger, press it back.
That's just my way of doing it!!.