Nice video! 

I think I can see a pretty distinct line around the "cast in" insert....  though it gets pretty fuzzy when I zoom in.  The insert could be loose in the case?  The edge of the insert is a circle just a little bigger than the bearing with 4 "bumps" around the circumference.  The location of those "bumps" correspond to dabs of silver-grey sealant on the outside of the case...  I think they represent locating pins that were sealed on the 77-78 cases.  Those four points can leak air.  Worse though is a loose insert.  If you dribble some oil around the "seam" and wipe off the surface, then you can push sideways on the insert with your fingers and if it's loose the oil that ran down in the groove will squeeze out.  Sometimes you can even feel the insert move. 

Many used cases have loose inserts, I don't like to use them.  I bought and returned several sets of cases on ebay before finding a good spare set...  which I think I ended up passing on to a member here.  I have heard stories of having the cases welded and/or machined to correct loose inserts. 

From memory, it seems the clutch half is more likely to have a very loose insert and it seems to me it's something that happens at higher miles...  but it could coincide with the knocking caused by a worn big end rod bearing?  Every IT175 engine I've taken apart with loose inserts had a big end rod bearing knock and the bearing was worn well beyond spec.  (Obviously on your engine the guy waited too long to rebuild the crank!)

Anyway, if you think the inserts are okay, I'd probably just use some proper loctite on the outer race of the bearing to hopefully keep it from spinning in the case. 

I do have a question on the bearing numbers...  do they have a "C4" designation on them?  If not, and if the old one didn't, that could be a reason the bearing may have spun in the case. 

Your Yamaha knowledge is incredible. Thanks for sharing.
I’m providing another video/photo link. Insert is loose, as you suggested may be the case, no pun intended. A couple of the photos are zooms of 1 of the 4 bumps that I thought might have a crack. But after close scrutiny, I think it’s a scratch. Are the 3 “dots” on the flip side of the insert where the sealant was injected to secure the insert permanently in place? If so, can the sealant be drilled out and replaced to solve the problem. Or do I need to start my search for new, used cases? 
photos.app.goo.gl/4AdNmeXabK4SvgSU7
 

Oh no!  That's the loosest insert I've ever seen.

As far as I know, inserts were cast in and held in place by solid metal.  I suspect the sealant spots are from where the insert was precisely supported during the casting process?  Though in 1979 Yamaha figured out a way to stop using the sealant as those spots can be problematic. 

Proper repair will require welding and machining in my opinion.  There are some skilled geniuses out there that would probably be able to do the job very well at a good price...  one guy I knew would have found it a fun challenge...  unfortunately he's no longer around.  

Used cases often have that problem...  as I hinted, 1979 (2W6 VIN prefix) cases are reportedly "improved" with regard to the inserts.  I had a good set of 79 cases but I think I sold them to a member here years ago.  I will look and see if I have any others.  If you find some on ebay, ask questions and be prepared to return them if the inserts are loose.  (It would be amazing if the clutch side insert in your cases was not loose as well...  plus I like to replace cases in matched sets if possible, sometimes a single doesn't match up perfectly)

Interference fit at room temperature.
Snug to slight press at temp. delta during assembly. (case v. bearing)
a bit above max operating temps. (200F or so)

Your pocket is puckered.


As is, the crank will orbit that end and take the bearing for a ride in the puckered pocket, making it peckered.
It will not be doing the opposite crank bearing and case any perks.

cliff

The clutch side is solid. I found some 2W 1979 cases. Waiting for seller to confirm that the inserts are solid. 
 I understand that the IT 175 engine is basically a bored out yz 125. Would 1979 yz cases work, if I were able to find some.
Ill ask around to find out if there are some highly regarded machine shops near me that may be able to take on the job of permanently affixing the inserts.
If you run across some 1979 case, please keep me in mind.

Thanks 

Please help me understand something.
Is the insert “stretched out” because the bore it sets in is loose and heat allowed the insert to expand. Even if a machinist can permanently affix the insert will it still be sloppy. 

Thanks

IT175 cases are unique.  IT175 cylinder will only fit on 77-79 IT175 cases as the transfer openings are much wider than that era YZ125 and 78-81 DT125/DT175 cases that both have the smaller transfer openings.  You'd have to weld extra material to the YZ125/DT125/DT175 cases and then grind the transfer openings bigger...  it's not a simple modification.

I'm guessing it wouldn't be easy at all to precisely center the inserts and fix them in place?  I imagine they'd weld up the inserts to secure them and add material to the bearing bore ID (or even remove the existing inserts and replace with something new) and then re-machine the bearing bore to the correct "press fit" size using the seal bore to center the new bearing bore...  

Hint: if you can see a distinct "outline" around the insert...  not just a color shade difference...  but something that looks like a line drawn around the insert...  that generally means the insert is loose, even if not as loose as yours! 

Cases I bought on ebay that had that line were all bad.  Make sure you ask, verify seller accepts returns, or verify the cases have the ebay "money back guarantee".  In my experience, some sellers will tell you the inserts are good and then when they're loose, claim it was used parts sold "as-is".  Ebay always backed me up but it can be a hassle and having seller email that said inserts were tight helped.  (Also, many sellers refused to provide any additional info beyond what they posted in the ad, might be risky to buy from them especially if they say "as-is")

As previously discussed, the bearing is a press fit on the ignition side of the crank and sometimes stays on the crank and the case bore is fine.  There is a risk on used cases that if the ignition side bearing is missing, the insert could be tight but the bore might be loose. 

Replacement cases are the best bet.  A repair is doable but means making up a very accurately made and solid alignment tool to hold everything in place (assuming the other bearing housing is in excellent condition) and centered while tack welding the insert in place while the cases are bolted together and then split for welding permanently.
The chance of case warpage is high and the repair would not be as strong as the original.

Sort of thing they do at work regularly, but there is a world of difference between repairing cases on obsolete £50K transmissions, they are thick cast iron with plenty of meat to go at, and a set of motorcycle crankcases from the 70s that are magnesium alloy, flimsy affairs.

I doubt any machine shop would take it on.  The job is difficult, the risks of it all going wrong are very high and the amount chargeable not worth the effort.

It would have to be a specialist, used to this kind of work, probably aerospace oriented that did it. 

A lot of great information and expertise from everyone.
It looks like there is one logical solution to the problem.
My quest for pre-owned cases begins. 

Thanks to all.