My Seca 750 is making some awful noises

Great progress. That's what the noise was all along. Are you going to replace the chain guide too?

 

That is so weird that after 40 years the bolts backed out. That looks to be the same as what happened to TheCrazyGnat

 

Yep, major engineering oversight.

 

I think I will probably replace the guide while I'm in there. Most everything looks quite good and clean, other than the starter clutch, of course.

I am worried about one of the half-circle shims for one of the transmission gear sets. When I lifted it out, I dropped one, and it basically disappeared. I hope it didn't drop through the timing chain tunnel...

 

Might be able to find it with a small pick up magnet if it's in the case.

 

Here's what the parts look like. Is there a bearing that the central gear runs on?

Nevermind. While looking for the shim/clip (which I still haven't found), I found the "collar" that the gear runs on.

 

While I'm waiting for parts, I think I will also tackle the steering head bearings. Might as well combine all the downtime into one.

 

Looks like I didn't actually lose one of those clips. There is only one per bearing. I thought the part I had removed had two and that I had lost one.

I reassembled the clutch hub today. I used Loctite red, and tightened the bolts to 22 lb feet. I think they'll stay put this time.

 

By the way, my crank counterweight also shows the same discoloration as was seen in that other starter clutch hub backed out screws thread. I wonder if the two bikes were made around the same time. Mine was 10/81.

 

Got my dental tubes in on Friday. Yesterday I welded one to the oil cooler center bolt to make the proper center bolt for my setup. Today I finished putting the bike back together and it's running again. Need to do some more tuning, or checking, initial idle stabilizer position seems too open. But, aside from that, sounds good. Normal cranking, no whining, etc.