Edited a bit on my last post

Done alot of commercial doors. Hinges were the worst to get a machined screw out of to remove a door…
My solution was to drill the Phillips head. 1/4” - 20 screw. I used a 1/4” drill bit. Drilled enough for the chamfered head to fall off… removed the hinge leaf and there was enuff screw to grab with a good pliers…

Schu, Just use a small center punch with a good pointed tip or sharp small chisel and tap it with a hammer on the outer edge of the screw. Then angle the punch or chisel in the counter clockwise direction (out ). Hit it a few times with a hammer . The screw will break loose then you can take it out the rest of the way with a screw driver. Simple and easy. It may take a few hits at the correct angle but never had one that i couldn't remove that way. Most likely it will ruin the screw too. Center punch works best for me. 

Also although Yamaha shows the same part number for the idle screws for 75-76, the idle screw springs are clearly different part numbers. Looking at pictures on e-bay of the 2 different springs by part numbers it looks like the 75 spring has closer coils which would bottom out sooner then the 76 spring so if using a 75 idle screw with 75 spring the idle screw may not go in as far.  
Also looking closely at the pictures of the idle screws the 76 looks to have a groove for a o-ring and the 75 idle screw doesn't even though they show to be the same part number? But odd they don't show a o-ring on the parts list. 

Once you get your oil leak fixed or crank seal replaced i would be sure you have a 76 idle screw (spring) for sure with what ever idle screw you are using. 
 

Thank you all for your suggestions. I will try and get back at it later this afternoon. Those magnified photos of the bugered up screw heads almost look like they might have been allen hex socket type screws instead of philips head.

And good catch on the different springs. I’m ok with the temporary screw and spring until I get my hands on the proper Yamaha parts, and I will then put the o-ring back on the screw.

I ordered new crank seals and crank o-ring that won’t be here for at least a week. I ordered Yamaha seals thru Babbits.

I used SKYDANCERS method for the upper screw because it had the necessary clearance to do so.
I used Morleys method for the lower screw because of clearance constraints, but both methods worked like a charm.
And I have confirmed that my crank seal just might be leaking. I am amazed it ran as well as it did with that entire upper section of the seal being gone. I wish I could say the missing rubber was laying where I could clear it out, but it is nowhere to be found. Oh well. It’s rubber, so it’s not like it could do much damage if it sucked it in.
imgur.com/a/TQsx98b
Next I will tear down the other side since I ordered that seal as well, and I have new clutch plates on the shelf. Can’t wait to see if I open a new can of worms on that side of the engine!


 

As I expected, removal of the clutch side cover has opened a whole nuther can of worms. I probably should start a new post on this, but instead I have decided to continue the saga of “O-ring on an idle screw” simply to show how one thing leads to another.

Once I removed the clutch side cover I immediately noticed two chunks of aluminum laying on the bottom surface inside the cover. I could not see any obvious signs of where they came from, so I set them aside and continued to remove the clutch assembly.

Once I flipped the clutch basket over I noticed that the 6 round bosses inside the primary driven gear were now 6 half-round bosses. The outer halves of the round steel bosses were chewed away leaving only half-rounds. I can see the suspect gear that did the chewing. The gear will be fine as is, but why did it happen?

Prior to removing the basket I had spun it by hand and there were no issues noticed. But then the damage was already done, so maybe I wouldn’t notice or feel anything being wrong. It appeared to have been assembled properly with the long spiral grooved spacer AND the flat washer.

So my theory on this one is that someone at some point had incorrectly assembled the clutch by leaving out the flat washer which allowed the basket to set too close inward. And once started, they soon realized the obvious clashing of metals. So they disassembled it all, cleaned MOST of the debris, and then reassembled it properly. My only concern is that the two chunks I found are aluminum and do not stick to a magnet. The 6 damaged bosses are steel….. so where did the aluminum chunks come from?

imgur.com/a/tNdpYHG

Edit:
The clutch side crank seal was also missing about 1/3 of its lip similar to the other side. I can’t believe the bike ran as good as it did with both crank seals bad.

Oh dear @#$%#$@^ i need a cuppa & a lie down after all that.
Another can of worms has started.
Hope we can help.
Motor sounded so perky too.

Update:
New crank seals and crank o-ring installed.
New friction plates installed.
However…….the manual says “check to see if the gear on the clutch housing is loose excessively due to the deterioration of damper rubber”.
imgur.com/a/wO4lt7T

So how loose is excessively loose?
Is this too loose?

 

Well the good thing is it isn't going to escape. You have plenty of play though before it finds the rubbers. What I'd do is look through various bigger motor models for the fat Oring that bikes like dt175 have that fits into the gap between gear & basket. That'll damp out the play albeit artificialy. I'll look later on computer, my fone is useless. 175 used that to stop chatter at idle that seemed to start when Ct2 went to a lighter flywheel with less inertia but that's irrelevant. I'm not talking those Oring between the plates just to be clear, but sits over the basket & in the V between gear & basket. Also to totally fix the play is a bit of a major & I know people have done it so they may link it to your post.