It's been the last year or so that all of these valve problems have been popping up... I don't remember being an issue for most of the life of this forum. All of the years of these bikes are different, and I haven't really kept up with mileage data. Maybe it's just that we have more members trying to fix a problem instead of people never posting and then just throwing their bikes, away. But it seems odd.

Anyway. The valve issue isn't something that happened because of you cranking the bike. A few different things had to fail all around the same time, and the broken gear and the subsequent searching for issues probably all boils down to this.

What kind of shape was your old head in? You'll also want the guides too. I don't recall the whole story. But if you have a good head on hand, then you're good to go. I'd just swap it over.

I really don't think it's a valve problem. I hand cranked again with the head fully assembled and the valve windows open and the most resistance happens a bit before the intake valves open up, not during any valve movement.
So after hand cranking it a bunch and not encountering anything too bad, I decided to try with the key again. This time got a whole new sound. Just realized I didn't dump a whole new load of oil in there this time, so it was just going with the dregs that were left over after I took the side off 2 weeks ago.
No terrible sounds tonight, a familiar failing sound that I forget the meaning of. What causes this one?
http://www.youtube.com/watch?v=1tan_b-vanM&edit=vd

Multi-problemed bike
 

I know this might sound stupid, but did you check for spark after putting everything back togeather?? Grandson and I still have not got his GZ going. Last time we took everything apart and then put it back and still would not start, We did find bad connection at pick-up coil to CDI connector. Fixed that and got spark back, but still no start for us. But did have spark back. Hang in there!!!! You are doing one hell of a job.

Ok, I've check for spark, then a second time checked for spark with a witness. Spark is strong and purpley and jumping across the gap, which is the right distance.

When I'm holding the starter, the engine does turn over, there is air being pushed out of the exhaust (so my camshaft prolly isn't snapped again :P )

We tried starting it with starter fluid (actual starter fluid that I bought from the store, nothing approximate about it), no go, but we did get a reversion that scared me...

I also tried running starting it twice on Thursday. The first time I got two loud backfires,
the second time it started, but sputtered out.

so... what now?

Ok, since I had reason to believe I had spark, air, fuel, and compression, I started looking for timing or other stuff that could be wrong. I eventually found isaac's thread called "No start: Have spark, have fuel, have air" in which he discovered that his woodruff key had been shorn off, thus allowing the flywheel to misalign and screw up the ignition timing.
If you'll remember from last page (about a month ago), I intially didn't tighten my flywheel on tight enough, well, as it turns out, that destroyed my woodruff key.
It took some time to figure out how to get it out, since the protruding part was completely flattened/gone.
Turns out that the semi-circular shape means you just have to push down on one end (by, say, tapping an awl on it with a hammer) and the other pops up and can just be pulled out, so it's not really an excuse for your friend to build his arc welder, but whatever, we got it.

I put a new one in today with great hopes that it would go, but it didn't. It was hot and it took us a long time to tighten everything down on my bike all proper-like, but yeah, it won't go. Turn over sounds, no catching. I'll take another look at it sometime next week, I guess.

Are you sure the cam timing is correct? I've never been inside one of these, just throwing an idea out.

It's definitely something I'll have to check again.
I'm missing the white line on the cam sprocket that's supposed to be at the front when it's timed, so even if did have it rightish, I may still be 180 off.

This is what makes me think cam timing. The most resistance should be just before the exhaust valves open.

I think you're right, however the most resistance is on the compression stroke, and both valves remain closed, then. So "just" meaning, after the piston goes down from the compression.

The exhaust valve should then remain open until the piston is at the top again. That is when the inlet valves should start opening. And the inlet valves should close when the piston is down again. Then, all valves should remain closed when the piston goes up, to the compression.

It was the woodruff key again. This time it didn't get shredded, it had just gotten pushed out when I was putting the rotor on or something.
Then the carb was gunked up and needed cleaning,
here's what it's doing now, what do you guys think I should do about it?
https://www.youtube.com/watch?v=s-CC1LpmGUU