For those who have rebuilt these idi's

[trapper]

as i am cleaning and prep the motor for the heads to go back on i notice that when i rotate the engine as the pistons move up and down it seems to leave behind a very thin coat of black oil im positive the rings are good and the pistons are very firm in the cylinders, is this an issue or is it just buildup on the rings underneath ?

 

[NMB2]

the rings dont sit metal to metal on the cylinder walls... there is a thin coat of oil between them. sounds normal to me.