Why is new part screaming?

[BTR]

2000 Explorer XLT 4DR 2WD. 4.0L SOHC JOB 1 (VIN E). 5-Speed Automatic O/D 5R55E. 158,000 miles.

I just installed a brand new FoMoCo idler pulley 6L2Z-6C348-A. It came with the bolt, and the front and back washers... it's a complete assembly. It screams like a scalded dog for about 4 seconds on startup, and then shuts up. Why does it do this? Is there some trick to installing them?

 

[wollimann]

The new pulley should not cause the noise. If the belt is fresh and lined up and the tensioner is not tired
the noise must came from other parts like alternator bearing, maybe AC clutch.
Maybe some debris in pulley grooves and belt is slipping for a short time?

 

[J_C]

Without the belt on, does it spin freely but with a "little" bit of resistance, not freewheelling long after spun by hand? It shouldn't keep spinning for several seconds or have any wobble.

Besides alignment and belt tension, I'd wonder if it's very old new stock and the grease inside has shelf rotted away. If it's bitter cold there right now, that can also contribute to temporarily hardened grease.