Cause of SR20DE Spun Bearing?

[Louis LaPrad]

OK. My dads engine is making a moderate (not extreme) knocking which sounds
like its coming from the head area.

He each plug wire out individually while it was running. When he pulls #3
out, there is no difference in idle or anything.

Is this a spun bearing?

This is my history:

I spun a bearing 3 years ago. My brother got his 91 SE-R at an auction and
it spun a bearing within 2 weeks. My dad bought his car (with a "freshly"
replaced junkyard engine) a month ago.

What causes this? It always seems to afflict cars that have sat for a while
(besides mine). Can this be prevented if I were to get a used SE-R to which
the condition was unknown?

Please tell me my dads car could have a different problem. I dont have the
heart to tell him to replace the engine.

Louis