Topic: Bought a 1978 seized engine

[crxnug]

I bought a engine that was on a bike someone bought and started it up and engine seized, found out engine was drained of oil. he got it un-seized and was selling it as a parts motor, i bought it for some parts but decided to remove heads and cylinders to see how bad it was. everything so far looks  really good, still had honing strokes on cylinder wall with no ridges   and pistons looked good, i still have to split the case to check bearing, what do you think would be the most likely issue that would be why it seized ( i know lack of oil,,,,) but where would i look for what made it seize, any help would be much appreciated

[low-side]

Usually with a lack of oil either the rings stick or something nasty happens to the rod and main bearings.  You might have gotten lucky and nothing serious happened (not likely though).

[Tracksnblades1]

Check the camshaft bearing surfaces in the holders 🙏.
I'd check all the oil pressure fed plain bearings, rods, mains, starter clutch gets oil from its nearby main bearing.
Does the engine turn over by hand now ?

[setdog]

sounds like you got the top end off with not obvious signs of damage such as a broken piston ring.  and youare already past the overhead cam, so that really only leaves the bottom end to inspect.  could be a rod bolt, could be a gear dog, only one way to find out and that is to crack it open, and inspect everything.

[Don R]

 I'm surprised the top end looked OK. Usually the cam towers go soon when there's no oil.

[crxnug]

Turns over freely. owner said after he un-seized it he never added oil and did a compression test after or restarted it, i will know better once i split the case and inspect   the bottom end