71 yamaha R5

[Greaser Greg]

This is the way these cases looked when opened and disassembled, minus the piles of rust between the bearings.  I'm glad I didn't make it run like that when it was together.  That rusty bearing does not turn.

[Greaser Greg]

Whoever invented the easy-out is "The Man"!

[Greaser Greg]

Used the wrong torque value and had the washer on backward for the primary shaft nut. Some manual's are WRONG!  Things started sounding funny so I went in to investigate and opened up a can of worms. Had a couple of issues while putting it back together.
First, one of the hub screw holes stripped, then a screw broke in my other hub!
Flushed the trans with oil and kerosene to try and get the aluminum out. There's probably more in the bearings so instead of opening the cases again already I'm just gonna keep changing the oil frequently (read "immediately") until there are no more sparkles. Probably not the best idea, but, whatever.
This bike was about half put together, and not quite how I wanted it. It had one new piston and an original burnt one, leaked air at all seals, frozen fork leg, so I took it apart and did my best. It finally was out on the street after a year in my shed, then the nut spun into the clutch case.
Here's what "Rusty" looked like on his first day out, whole again, after 30-some years! 
Waiting for a few items from economy cycle to get some more stuff in order. Rubber bits, wiring loom, etc. 

[85RZwade]

Good to see someone making progress!
Wade

[Greaser Greg]

I've ridden the bike about four hours since assembly and its seized. Any suggestions before I take the top off? Pulled the clutch cover and looks fine. Moving rear wheel in first moves the clutch a smidge, but not the primary gear. Going to look at plugs for clues . 
Edit: they look good.

[Jspooner]

Could be timing, jetting, air leak, are you running the pump or premix? Could be lots different reasons why.

[Greaser Greg]

Oil lines are full and pump tested fine before. Main concern now is getting the motor unstuck so I can look for damage, and check timing, right? Can't really do a pressure test since the ports might be blocked by Pistons, no? Jests are on the big side and plugs are caramel colored.

[Jspooner]

Was this a complete rebuild? New crank and everything?

[Greaser Greg]

Yes, everything new.

[pdxjim]

Bummer, Greg.

Can you describe the situation when it seized?  RPM, air temp, bike hot or cold, any noises beyond the usual?

Did it just lock solid all at once?

If both plugs look good, that probably eliminates detonation and a ventilated piston crown.

[Greaser Greg]

Seemed almost like it ran out of gas, died. Bump started it to get through a dark curve in the road, went a few meters, rear wheel locked up... Plenty of gas, so...? No horrible banging sounds or anything. Hopefully just needs rings and a hone! And everything checked, again. Not very cold here, around 50*F. Bike was plenty warmed up. Was taking it easy in the dark so, we shall see. Maybe my tank is rusty and clogged the petcock.  guess I'll check the torque on head bolts just for kicks.

[Barrie]

From the description, sounds like a bottom end mechanical problem , not oil, lift the heads and see how much lubricant is in evidence , go from there